What is Biological Control?

This segment includes several paragraphs with general information about biological control and these subsections:

  • Conservation
  • Classical Biological Control
  • Augmentation
  • Purchase and Release of Natural Enemies

Biological control is a component of an integrated pest management strategy. It is defined as the reduction of pest populations by natural enemies and typically involves an active human role. Keep in mind that all insect species are also suppressed by naturally occurring organisms and environmental factors, with no human input. This is frequently referred to as natural control. This guide emphasizes the biological control of insects but biological control of weeds and plant diseases is also included. Natural enemies of insect pests, also known as biological control agents, include predators, parasitoids, and pathogens. Biological control of weeds includes insects and pathogens. Biological control agents of plant diseases are most often referred to as antagonists.
Predators, such as lady beetles and lacewings, are mainly free-living species that consume a large number of prey during their lifetime. Parasitoids are species whose immature stage develops on or within a single insect host, ultimately killing the host. Many species of wasps and some flies are parasitoids. Pathogens are disease-causing organisms including bacteria, fungi, and viruses. They kill or debilitate their host and are relatively specific to certain insect groups. Each of these natural enemy groups is discussed in much greater detail in following sections.
The behaviors and life cycles of natural enemies can be relatively simple or extraordinarily complex, and not all natural enemies of insects are beneficial to crop production. For example, hyperparasitoids are parasitoids of other parasitoids. In potatoes grown in Maine, 22 parasitoids of aphids were identified, yet these were attacked by 18 additional species of hyperparasitoids.
This guide concentrates on those species for which the benefits of their presence outweigh any disadvantages. A successful natural enemy should have a high reproductive rate, good searching ability, host specificity, be adaptable to different environmental conditions, and be synchronized with its host (pest).
A high reproductive rate is important so that populations of the natural enemy can rapidly increase when hosts are available. The natural enemy must be effective at searching for its host and it should be searching for only one or a few host species. Spiders, for example, feed on many different hosts including other natural enemies. It is also very important that the natural enemy occur at the same time as its host. For example, if the natural enemy is an egg parasitoid, it must be present when host eggs are available. No natural enemy has all these attributes, but those with several characteristics will be more important in helping maintain pest populations.
There are three broad and somewhat overlapping types of biological control: conservation, classical biological control (introduction of natural enemies to a new locale), and augmentation.


Conservation
The conservation of natural enemies is probably the most important and readily available biological control practice available to growers. Natural enemies occur in all production systems, from the backyard garden to the commercial field. They are adapted to the local environment and to the target pest, and their conservation is generally simple and cost-effective. With relatively little effort the activity of these natural enemies can be observed. Lacewings, lady beetles, hover fly larvae, and parasitized aphid mummies are almost always present in aphid colonies. Fungus-infected adult flies are often common following periods of high humidity. These natural controls are important and need to be conserved and considered when making pest management decisions. In many instances the importance of natural enemies has not been adequately studied or does not become apparent until insecticide use is stopped or reduced. Often the best we can do is to recognize that these factors are present and minimize negative impacts on them. If an insecticide is needed, every effort should be made to use a selective material in a selective manner.
Examples of classical biological control:
Left: An egg parasitoid introduced from Europe for biological control of southern green stink bug. J.K.Clark, University of California Statewide IPM Project
Center:A European weevil imported to attack purple loosestrife. B.Blossey
Right: A successfully introduced lady beetle. J.Ogrodnick
Classical biological control
In many instances the complex of natural enemies associated with an insect pest may be inadequate. This is especially evident when an insect pest is accidentally introduced into a new geographic area without its associated natural enemies. These introduced pests are referred to as exotics and comprise about 40% of the insect pests in the United States. Examples of introduced vegetable pests include the European corn borer, one of the most destructive insects in North America. To obtain the needed natural enemies, we turn to classical biological control. This is the practice of importing, and releasing for establishment, natural enemies to control an introduced (exotic) pest, although it is also practiced against native insect pests. The first step in the process is to determine the origin of the introduced pest and then collect appropriate natural enemies (from that location or similar locations) associated with the pest or closely related species. The natural enemy is then passed through a rigorous quarantine process, to ensure that no unwanted organisms (such as hyperparasitoids) are introduced, then reared, ideally in large numbers, and released. Follow-up studies are conducted to determine if the natural enemy successfully established at the site of release, and to assess the long-term benefit of its presence.
There are many examples of successful classical biological control programs. One of the earliest successes was with the cottony cushion scale, a pest that was devastating the California citrus industry in the late 1800s. A predatory insect, the vedalia beetle, and a parasitoid fly were introduced from Australia. Within a few years the cottony cushion scale was completely controlled by these introduced natural enemies. Damage from the alfalfa weevil, a serious introduced pest of forage, was substantially reduced by the introduction of several natural enemies. About 20 years after their introduction, the alfalfa acreage treated for alfalfa weevil in the northeastern United States was reduced by 75 percent. A small wasp, Trichogramma ostriniae, introduced from China to help control the European corn borer, is a recent example of a long history of classical biological control efforts for this major pest. Many classical biological control programs for insect pests and weeds are under way across the United States and Canada.
Classical biological control is long lasting and inexpensive. Other than the initial costs of collection, importation, and rearing, little expense is incurred. When a natural enemy is successfully established it rarely requires additional input and it continues to kill the pest with no direct help from humans and at no cost. Unfortunately, classical biological control does not always work. It is usually most effective against exotic pests and less so against native insect pests. The reasons for failure are often not known, but may include the release of too few individuals, poor adaptation of the natural enemy to environmental conditions at the release location, and lack of synchrony between the life cycle of the natural enemy and host pest.
Augmentation
This third type of biological control involves the supplemental release of natural enemies. Relatively few natural enemies may be released at a critical time of the season (inoculative release) or literally millions may be released (inundative release). Additionally, the cropping system may be modified to favor or augment the natural enemies. This latter practice is frequently referred to as habitat manipulation.
An example of inoculative release occurs in greenhouse production of several crops. Periodic releases of the parasitoid, Encarsia formosa, are used to control greenhouse whitefly, and the predaceous mite, Phytoseiulus persimilis, is used for control of the two-spotted spider mite.
Lady beetles, lacewings, or parasitoids such as Trichogramma are frequently released in large numbers (inundative release). Recommended release rates for Trichogramma in vegetable or field crops range from 5,000 to 200,000 per acre per week depending on level of pest infestation. Similarly, entomopathogenic nematodes are released at rates of millions and even billions per acre for control of certain soil-dwelling insect pests.
Habitat or environmental manipulation is another form of augmentation. This tactic involves altering the cropping system to augment or enhance the effectiveness of a natural enemy. Many adult parasitoids and predators benefit from sources of nectar and the protection provided by refuges such as hedgerows, cover crops, and weedy borders.
Natural enemies can benefit from a source of nectar. Attractive flowers include, from left to right, wild carrot (A.T.Eaton), dill (M.Hoffmann), and goldenrod (M.Hoffmann).
Mixed plantings and the provision of flowering borders can increase the diversity of habitats and provide shelter and alternative food sources. They are easily incorporated into home gardens and even small-scale commercial plantings, but are more difficult to accommodate in large-scale crop production. There may also be some conflict with pest control for the large producer because of the difficulty of targeting the pest species and the use of refuges by the pest insects as well as natural enemies.
Examples of habitat manipulation include growing flowering plants (pollen and nectar sources) near crops to attract and maintain populations of natural enemies. For example, hover fly adults can be attracted to umbelliferous plants in bloom.
Recent work in California has demonstrated that planting prune trees in grape vineyards provides an improved overwintering habitat or refuge for a key grape pest parasitoid. The prune trees harbor an alternate host for the parasitoid, which could previously overwinter only at great distances from most vineyards. Caution should be used with this tactic because some plants attractive to natural enemies may also be hosts for certain plant diseases, especially plant viruses that could be vectored by insect pests to the crop. Although the tactic appears to hold much promise, only a few examples have been adequately researched and developed.
Release packs for mass reared natural enemies vary in form and function. From left,Trichogramma wasps (M.Hoffmann), Encarsia wasps (J.Sanderson), and Orius bugs (J.Sanderson).
Purchase and Release of Natural Enemies
Many commercial insectaries rear and market a variety of natural enemies including predaceous mites, lady beetles, lacewings, praying mantids, and several species of parasitoids. Success with such releases requires appropriate timing (the host must be present or the natural enemy will simply die or leave the area) and release of the correct number of natural enemies per unit area (release rate). In many cases, the most effective release rate has not been identified as it will vary depending on crop type and target host density.
Success also requires a healthy and robust natural enemy. This guide does not make specific recommendations about the purchase or release of the commercially available natural enemies, but it does provide essential information about the biology and behavior of most commercially reared species. This information should be helpful in making decisions regarding their use.

Biocontrol Lab

Introduced Species, often referred to as invasive species, are non-native organisms that are introduced to a new environment. Since the new environment for these introduced species often does not have the same predators that were in the native environment, their populations can increase unchecked by natural enemies. Introduced species out-compete native species for natural resources, thus taking over a native species niche.

Biocontrol, short for Biological Control, is the management of a pest, typically invasive species, by introducing a natural predator into the environment. Biocontrol reduces the pest population and their impacts on the environment. Biocontrol has many advantages. Natural enemies are an environmentally friendly alternative to pesticides that are often used to control invasive species. Biocontrol is long term and sustainable, the major cost for controlling an introduced species is the research involved in determining the safety and effectiveness of a biocontrol agent. Therefore biocontrol can be cost effective in the long-term. The University of Rhode Island Insect Biological Control lab has many ongoing biocontrol projects for Rhode Island invasive species, to help reduce a pests’ ecological and social impacts.

To learn more information on Managing Invasive Plants check out this link to U.S Fish and Wildlife Services

Biological Control Program

Biological control can be defined as the deliberate use of natural enemies – predators, parasites, pathogens, and competitors to suppress and maintain populations of a target pest species (insects, mites, weeds, plant pathogens, and other pest organisms).

NIFA supports research in bio-based pest management, which has the goal of providing safer and more effective methods of controlling pests while reducing our reliance on synthetic pesticides.

Biological control is particularly desirable because the tactic is environmentally safe, energy self-sufficient, cost-effective, sustainable, and can be readily incorporated into integrated pest management (IPM) programs. Furthermore, in many cases benefits from the use of natural enemies accrue at no additional cost. The practice of biological control usually involves one or more of the following approaches: 1) the importation of exotic natural enemies (classical biological control); 2) the conservation of resident or introduced beneficial organisms; and 3) the mass production and periodic release of natural enemies.

Biological control is often an important component of IPM programs, and is considered one of a number of bio-based pest management tactics. Other bio-based strategies include the use of microbial pesticides, behavior-modifying chemicals, genetic manipulation of pests, and host plant resistance.

Other agronomic or exclusionary tactics, such as date of planting, crop rotation, intercropping, and early maturing varieties, are based on knowledge of the interactions among pests, beneficial organisms, crops, and their environment. These tools may further enhance the implementation and success of bio-based pest management approaches including biological control.

Efforts in Controlling Invasive Species

NIFA is an active member of the federal National Invasive Species Council and contributes to the Invasive Species Management Plan, which includes an action plan for managing invasive species. A part of this plan recommends that the USDA accelerate the development, testing, assessment, transfer, and post-release monitoring of environmentally safe biological control agents.

Program Type:Emphasis Area Program Contact: Robert M. Nowierski External Resources

  • Biological Pest Control Definition, New World Encyclopedia
  • The Association of Natural Biocontrol Producers (ANBP)
  • UC IPM Statewide Integrated Pest Management Program
  • International Organisation for Biological Control (IOBC)
  • Plant Management in Florida Waters, University of Florida

Related Information

Topic Pest Management

“Brood” nematodes are mixed with the appropriate nutrients to encourage them to multiply. After an incubation period, they are “fed”, where they rapidly multiply squillionfold, enter an all-important “infective juvenile” stage and are subsequently “harvested”. Samples are laboratory-tested before batches are prepared for sale, packed in cartons and put in cold storage before dispatch.

The production process requires intricate planning to meet supply and demand, which is determined by seasons and soil temperature. My tour may read like a horror story, but I was fascinated.

Biological warfare for beginners

Use water-in nematodes outdoors against:

  • Slugs, ant nests (dependent on soil temperature).
  • Leatherjackets, chafer grubs (in April and October, to coincide with vulnerable parts of their life cycles).
  • Carrot fly, cabbage root fly, cutworms, onion fly, sciarid fly, caterpillars, gooseberry sawfly, thrips and codling moth (all can be attacked with a single product).

Use water-in nematodes indoors and out against:

  • Vine weevils, sciarid fly (both dependent on soil temperature).

Use predators indoors against:

  • Whitefly (Encarsia wasp), red spider (Phytoseiulus mite), mealy bug (Cryptolaemus larvae).

Buy and apply

  • Packs are usually sold via mail order (see nemasysinfo.com for stockists).and delivered at the optimum time for application (taking into account north/south soil temperature difference).
  • Follow instructions about storage and application methods to the letter.
  • Use a soil thermometer, not guesswork. Once you get the hang of this, it is less fiddly than it sounds.
  • Nematodes will only snap into action when added to water and applied to already moist soil. Apply in the evening since soil rarely dries out overnight.
  • Results may not be obvious instantly, and you will see no corpses.
  • See the RHS website for further information about biological pest control.
  • Visit greengardener.co.uk for other non-chemical pest controls such as barriers and natural sprays.

Nematodes

What are they?

With over 20,000 classified species, and a possible million unclassified, nematodes are the most numerous multicellular animals on earth. A handful of soil will contain thousands of these microscopic worms, many of them acting as parasites on insects, plants or animals.

Nematodes can be beneficial or harmful. Gardeners use them as a biological control on many plant pests, such as slugs, chafer grubs, vine weevil and sawfly. But some nematodes, such as the potato cyst, also cause huge damage to crops. See Further Reading, below.

How do they work?

If you apply nematodes to the pest – either in the soil or on the plant – the nematode ejects bacteria inside the pest’s body. These bacteria multiply and cause blood poisoning, leading to death. The host tissue is then fed on by the nematodes, and as they feed they multiply, and immediately start searching for a new host.

For the organic grower, this is a biological – not chemical – pest control. It also has the advantage of being reasonably specific to the target pest, so that other wildlife is not affected. You can buy nematodes online. However, they aren’t necessarily cheap and you do need to follow the precise instructions.

How to use nematodes

It is important to choose the correct nematode for the right type of pest. And to use them in the right conditions ie when the soil is above 5C (and will remain so) and when pests or their larvae are active. Nematodes are also light sensitive, so use them early morning or dusk, when light levels are low.

They arrive in a sachet suspended in a paste. It is best to use them straight away, however you can store them in the fridge for up to a few weeks (do not freeze). Mix the paste with a small amount of water to make a slurry, before adding the rest of the water. Stir the solution once again before applying. If you use a watering can, use a coarse rose, to make sure that the nematodes don’t get stuck in the holes.

Keep the soil moist and warm for at least a few weeks, to make sure that the nematodes remain active. You may have to make repeat applications – especially when treating slugs, for instance.

How Long Does It Take To See Results?

Usually 3-7 days, with maximum effect occurring over 2-4 weeks. Nematodes disintegrate the pests from the inside out, so you will not see dead insect bodies as you would with a chemical knockdown.

How Often Should Nematodes Be Applied?

Nematodes are recommended for use whenever larvae or grubs are present. Generally, this is during the spring and autumn. Because larvae feed on plant roots, beneath the soil surface, severe damage can be done before realizing there is a problem. Look for signs of an adult insect, such as leaf-notching. If adult insects are present, their eggs will be hatching soon. Again, you may have to make repeat applications.

Where can I get nematodes?

You can buy them online. We recommend the range from the Organic Gardening Catalogue.

The following is a list of pests, and the best nematodes to deal with them:

Ants Nematode Steinernema will ambush the ants when passing. As the bacteria poisons them, it will weaken the colony, eventually killing off the queen who has too few workers to feed her. It is best used between April to September by drenching the nests.

Chafer grubs If your lawn has yellow patches and looks like it has been dug up, chances are you have chafer grubs. The damage comes from the birds, foxes and badgers who dig for these tasty morsels. The grubs can be controlled by the nematode Heterorhabitis bacteriophora, one of the oldest known and best of the insect parasitic nematodes. It is best to deal with the young grubs in August and early September.

Fruit flies, carrot root fly, onion fly, gooseberry sawfly and codling moth. All these pests can be treated with a generic mix called Nemasys Natural Fruit and Veg Protection Pest Control. You can use it as a general treatment after planting out and when the soil has warmed up, or to target specific pests when you see them, such as gooseberry sawfly caterpillars. These (and other caterpillars) need to have direct contact with the spray while they are on the leaves.

Leather jackets Leatherjackets, the larvae of the crane fly or daddy longlegs, attack the roots of your grass lawn. They can be controlled by the nematodes Steinernema feltiae. The best time to put them to work is in the autumn, when the adult daddy-long-legs are laying and the soil is warm.

Slugs The grandly named Phasmarhabditis hermaphrodita is another weapon in the arsenal against slugs. The nematodes can modify the slug’s behaviour so that it remains below the ground surface before death. After eating the cadaver, they produce another generation, which move off through the soil in search of new slug hosts.

Vine weevils Steinernema kraussei seeks out the Vine Weevil larvae. Unusually, this nematode is active at soil temperatures as low as 5C, which means that applications can start in March in many areas. This will give much greater control of larvae when they are present – either March to May, or from July to October.

Further reading

Nematodes can also destroy a crop. The worst examples are the potato cyst. To prevent infestation, use a crop rotation of at least 3 years and buy resistant varieties where possible.

Here also is some research on the nematodes which devastate legume crops, particularly clover http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1088311/

And some interesting information on how the American fruit fly has evolved to fight back against the nematode. https://www.theguardian.com/science/2010/jul/08/bacteria-fruit-fly-nematode-parasite

Biological control

Biological control, the use of living organisms to control pests. A natural enemy such as a parasite, predator, or disease organism is introduced into the environment of a pest or, if already present, is encouraged to multiply and become more effective in reducing the number of pest organisms. Examples of biological control include the destruction of the citrophilus mealybug in California by two parasitic species of chalcid wasps imported from Australia, Coccophagus gurneyi and Tetracnemus pretiosus; the effective predation of an Australian ladybird beetle, or vedalia beetle (Rodolia cardinalis), on the cottony cushion scale in California; the limiting of the proliferation of the European rabbit in Australia by introduction of myxoma virus (which causes the disease myxomatosis); the control of Japanese beetles by Bacillus popilliae, which causes milky disease; and the control of various larvae that attack food crops in home gardens by Bacillus thuringiensis, a soil-dwelling bacterium.

Read More on This Topic plant disease: Biological control Biological control of plant diseases involves the use of organisms other than humans to reduce or prevent infection by…

While biological control can be an effective and environmentally sound means of controlling pests, some strategies have led to the introduction of invasive species into novel habitats, such as the venomous cane toads (Bufo marinus) introduced in Australia in the 1930s from Hawaii to reduce the effects of beetles on sugarcane plantations. Cane toads have been responsible for a variety of ills, such as population declines in native prey species (bees and other small animals), population drops in amphibian species that compete with them, and the poisoning of species that consume them. Any new methods of biological control must be carefully considered before organisms are released into the environment.

Biological pest control

Biological control, biocontrol, or biological pest control is a method of suppressing or controlling the population of undesirable insects, other animals, or plants by the introduction, encouragement, or artificial increase of their natural enemies to economically non–important levels. It is an important component of integrated pest management (IPM) programs (Weeden et al. 2007).

The biological control of pests and weeds relies on predation, parasitism, herbivory, or other natural mechanisms. Therefore, it is the active manipulation of natural phenomena in serving human purpose, working harmoniously with nature. A successful story of biological control of pests refer to the human beings’ capability to depict natural processes for their use and can be the most harmless, non–polluting, and self–perpetuating control method.

Predatory Polistes wasp looking for bollworms or other caterpillars on a cotton plant

Contents

  • 1 Overview
  • 2 Strategies of biological control methods
    • 2.1 Conservation biocontrol
    • 2.2 Classical biological control
    • 2.3 Augmentative biological control
  • 3 Different types of biological control agents
    • 3.1 Predators
    • 3.2 Parasitoidal insects
    • 3.3 Parasitic nematodes
    • 3.4 Plants to regulate insect pests
    • 3.5 Pathogens to be used as biopesticides
  • 4 Significance of biological control
  • 5 Negative results of biological control
  • 6 References
  • 7 Credits

Overview

Diagram illustrating the natural enemies of cabbage pests

In biological control, the reduction of pest populations is achieved by actively using natural enemies.

Natural enemies of the pests, also known as biological control agents, include predatory and parasitoidal insects, predatory vertebrates, nematode parasites, protozoan parasites, and fungal, bacterial, as well as viral pathogens (Metcalf et al. 1973). Biological control agents of plant diseases are most often referred to as antagonists. Biological control agents of weeds include herbivores and plant pathogens. Predators, such as lady beetles and lacewings, are mainly free–living species that consume a large number of prey during their lifetime. Parasitoids are species whose immature stage develops on or within a single insect host, ultimately killing the host. Most have a very narrow host range. Many species of wasps and some flies are parasitoids. Pathogens are disease–causing organisms including bacteria, fungi, and viruses. They kill or debilitate their host and are relatively specific to certain pest or weed groups.

Strategies of biological control methods

There are three basic types of biological control strategies; conservation biocontrol, classical biological control, and augmentative biological control (biopesticides).

Conservation biocontrol

The conservation of existing natural enemies is probably the most important and readily available biological control practice available to homeowners and gardeners. Natural enemies occur in all areas, from the backyard garden to the commercial field. They are adapted to the local environment and to the target pest, and their conservation is generally simple and cost–effective. For example, snakes consume a lot or rodent and insect pests that can be damaging to agricultural crops or spread disease. Dragonflies are important consumers of mosquitoes.

Eggs, larvae, and pupae of Helicoverpa moths, the main insect pests of cotton, are all attacked by many beneficial insects and research can be conducted in identifying critical habitats, resources needed to maintain them, and ways of encouraging their activity (Lawrence 2005). Lacewings, lady beetles, hover fly larvae, and parasitized aphid mummies are almost always present in aphid colonies. Fungus–infected adult flies are often common following periods of high humidity. These naturally occurring biological controls are often susceptible to the same pesticides used to target their hosts. Preventing the accidental eradication of natural enemies is termed simple conservation.

Classical biological control

Classical biological control is the introduction of exotic natural enemies to a new locale where they did not originate or do not occur naturally. This is usually done by government authorities.

In many instances, the complex of natural enemies associated with an insect pest may be inadequate. This is especially evident when an insect pest is accidentally introduced into a new geographic area without its associated natural enemies. These introduced pests are referred to as exotic pests and comprise about 40 percent of the insect pests in the United States. Examples of introduced vegetable pests include the European corn borer, one of the most destructive insects in North America.

To obtain the needed natural enemies, scientists have utilized classical biological control. This is the practice of importing, and releasing for establishment, natural enemies to control an introduced (exotic) pest, although it is also practiced against native insect pests. The first step in the process is to determine the origin of the introduced pest and then collect appropriate natural enemies associated with the pest or closely related species. The natural enemy is then passed through a rigorous quarantine process, to ensure that no unwanted organisms (such as hyperparasitoids or parasites of the parasite) are introduced, then they are mass produced, and released. Follow–up studies are conducted to determine if the natural enemy becomes successfully established at the site of release, and to assess the long–term benefit of its presence.

There are many examples of successful classical biological control programs. One of the earliest successes was with the cottony cushion scale (Icerya purchasi), a pest that was devastating the California citrus industry in the late 1800s. A predatory insect, the Australian lady beetle or vedalia beetle (Rodolia cardinalis), and a parasitoid fly were introduced from Australia. Within a few years, the cottony cushion scale was completely controlled by these introduced natural enemies (Metcalf et al. 1973). Damage from the alfalfa weevil, a serious introduced pest of forage, was substantially reduced by the introduction of several natural enemies like imported ichnemonid parasitoid Bathyplectes curculionis. About twenty years after their introduction, the alfalfa area treated for alfalfa weevil in the northeastern United States was reduced by 75 percent (Metcalf et al. 1973). A small wasp, Trichogramma ostriniae, introduced from China to help control the European corn borer (Pyrausta nubilalis), is a recent example of a long history of classical biological control efforts for this major pest. Many classical biological control programs for insect pests and weeds are under way across the United States and Canada.

Classical biological control is long lasting and inexpensive. Other than the initial costs of collection, importation, and rearing, little expense is incurred. When a natural enemy is successfully established it rarely requires additional input and it continues to kill the pest with no direct help from humans and at no cost. Unfortunately, classical biological control does not always work. It is usually most effective against exotic pests and less so against native insect pests. The reasons for failure are often not known, but may include the release of too few individuals, poor adaptation of the natural enemy to environmental conditions at the release location, and lack of synchrony between the life cycle of the natural enemy and host pest.

Augmentative biological control

This third strategy of biological control method involves the supplemental release of natural enemies. Relatively few natural enemies may be released at a critical time of the season (inoculative release) or literally millions may be released (inundative release). Additionally, the cropping system may be modified to favor or augment the natural enemies. This latter practice is frequently referred to as habitat manipulation.

An example of inoculative release occurs in greenhouse production of several crops. Periodic releases of the parasitoid, Encarsia formosa, are used to control greenhouse whitefly, and the predaceous mite, Phytoseilus persimilis, is used for control of the two–spotted spider mite. The wasp Encarsia formosa lays its eggs in young whitefly “scales,” turning them black as the parasite larvae pupates. Ideally it is introduced as soon as possible after the first adult whitefly are seen. It is most effective when dealing with low level infestations, giving protection over a long period of time. The predatory mite, Phytoseilus persimilis, is slightly larger than its prey and has an orange body. It develops from egg to adult twice as fast as the red spider mite and once established quickly overcomes infestation.

Diagram illustrating the life cycles of Greenhouse whitefly and its parasitoid wasp Encarsia formosa

Lady beetles, lacewings, or parasitoids such as Trichogramma are frequently released in large numbers (inundative release) and are often known as biopesticides. Recommended release rates for Trichogramma in vegetable or field crops range from 5,000 to 200,000 per acre per week depending on level of pest infestation. Similarly, entomoparasitic nematodes are released at rates of millions and even billions per acre for control of certain soil-dwelling insect pests. Entomopathogenic fungus Metarhizium anisopliae var. acridum, which is specific to species of short–horned grasshoppers (Acridoidea and Pyrgomorphoidea) widely distributed in Africa, has been developed as inundative biological control agent (LUBILOSA 2004).

Habitat or environmental manipulation is another form of augmentation. This tactic involves altering the cropping system to augment or enhance the effectiveness of a natural enemy. Many adult parasitoids and predators benefit from sources of nectar and the protection provided by refuges such as hedgerows, cover crops, and weedy borders. Mixed plantings and the provision of flowering borders can increase the diversity of habitats and provide shelter and alternative food sources. They are easily incorporated into home gardens and even small-scale commercial plantings, but are more difficult to accommodate in large–scale crop production. There may also be some conflict with pest control for the large producer because of the difficulty of targeting the pest species and the use of refuges by the pest insects as well as natural enemies.

Examples of habitat manipulation include growing flowering plants (pollen and nectar sources) near crops to attract and maintain populations of natural enemies. For example, hover fly adults can be attracted to umbelliferous plants in bloom.

Biological control experts in California have demonstrated that planting prune trees in grape vineyards provides an improved overwintering habitat or refuge for a key grape pest parasitoid. The prune trees harbor an alternate host for the parasitoid, which could previously overwinter only at great distances from most vineyards. Caution should be used with this tactic because some plants attractive to natural enemies may also be hosts for certain plant diseases, especially plant viruses that could be vectored by insect pests to the crop. Although the tactic appears to hold much promise, only a few examples have been adequately researched and developed.

Different types of biological control agents

Predators

Ladybird larva eating wooly apple aphids

Ladybugs, and in particular their larvae which are active between May and July in the northern hemisphere, are voracious predators of aphids such as greenfly and blackfly, and will also consume mites, scale insects, and small caterpillars. The ladybug is a very familiar beetle with various colored markings, while its larvae are initially small and spidery, growing up to 17 millimeters (mm) long. The larvae have a tapering segmented gray/black body with orange/yellow markings nettles in the garden and by leaving hollow stems and some plant debris over–winter so that they can hibernate over winter.

Hoverflies, resembling slightly darker bees or wasps, have characteristic hovering, darting flight patterns. There are over 100 species of hoverfly, whose larvae principally feed upon greenfly, one larva devouring up to 50 a day, or 1000 in its lifetime. They also eat fruit tree spider mites and small caterpillars. Adults feed on nectar and pollen, which they require for egg production. Eggs are minute (1 mm), pale yellow-white, and laid singly near greenfly colonies. Larvae are 8–17 mm long, disguised to resemble bird droppings; they are legless and have no distinct head. Therefore, they are semi–transparent with a range of colors from green, white, brown, and black. Hoverflies can be encouraged by growing attractant flowers such as the poached eggplant (Limnanthes douglasii), marigolds, or phacelia throughout the growing season.

Dragonflies are important predators of mosquitoes, both in the water, where the dragonfly naiads eat mosquito larvae, and in the air, where adult dragonflies capture and eat adult mosquitoes. Community–wide mosquito control programs that spray adult mosquitoes also kill dragonflies, thus removing an important biocontrol agent, and can actually increase mosquito populations in the long term.

Other useful garden predators include lacewings, pirate bugs, rove and ground beetles, aphid midge, centipedes, as well as larger fauna such as frogs, toads, lizards, hedgehogs, slow–worms, and birds. Cats and rat terriers kill field mice, rats, june bugs, and birds. Dogs chase away many types of pest animals. Dachshunds are bred specifically to fit inside tunnels underground to kill badgers.

Parasitoidal insects

Most insect parasitoids are wasps or flies. For example, the parasitoid Gonatocerus ashmeadi (Hymenoptera: Mymaridae) has been introduced to control the glassy-winged sharpshooter Homalodisca vitripennis (Hemipterae: Cicadellidae) in French Polynesia and has successfully controlled about 95 percent of the pest density (Hoddle et al. 2006). Parasitiods comprise a diverse range of insects that lay their eggs on or in the body of an insect host, which is then used as a food for developing larvae. Parasitic wasps take much longer than predators to consume their victims, for if the larvae were to eat too fast they would run out of food before they became adults. Such parasites are very useful in the organic garden, for they are very efficient hunters, always at work searching for pest invaders. As adults, they require high–energy fuel as they fly from place to place, and feed upon nectar, pollen and sap, therefore planting plenty of flowering plants, particularly buckwheat, umbellifers, and composites will encourage their presence.

Four of the most important groups are:

  • Ichneumonid wasps: (5–10 mm) Prey mainly on caterpillars of butterflies and moths.
  • Braconid wasps: Tiny wasps (up to 5 mm) attack caterpillars and a wide range of other insects including greenfly. It is a common parasite of the cabbage white caterpillar, seen as clusters of sulphur yellow cocoons bursting from collapsed caterpillar skin.
  • Chalcid wasps: Among the smallest of insects (<3 mm). It parasitizes eggs/larvae of greenfly, whitefly, cabbage caterpillars, scale insects, and strawberry tortrix moth.
  • Tachinid flies: Parasitize a wide range of insects including caterpillars, adult and larval beetles, true bugs, and others.

Parasitic nematodes

Nine families of nematodes (Allantone-matidae, Diplogasteridae, Heterorhabditidae, Mermithidae, Neotylenchidae, Rhabditidae, Sphaerulariidae, Steinernematidae, and Tetradonematidae) include species that attack insects and kill or sterilize them, or alter their development (UN–LN 2003). In addition to insects, nematodes can parasitize spiders, leeches, [[annelid[[s, crustaceans and mollusks. An excellent example of a situation in which a nematode may replace chemicals for control of an insect is the black vine weevil, Otiorhynchus sulcatus, in cranberries. Uses of chemical insecticides on cranberry either are restricted or have not provided adequate control of black vine weevil larvae. Heterorhabditis bacteriophora NC strain was applied, and it provided more than 70 percent control soon after treatment and was still providing that same level of control a year later (Shanks 1990).

Many nematode–based products are currently available. They are formulated from various species of Steinernema and Heterorhabditis. Some of the products found in various countries are ORTHO Bio–Safe, BioVector, Sanoplant, Boden-Ntitzlinge, Helix, Otinem, Nemasys, and so forth (Smart 1995). A fairly recent development in the control of slugs is the introduction of “Nemaslug,” a microscopic nematode (Phasmarhabditis hermaphrodita) that will seek out and parasitize slugs, reproducing inside them and killing them. The nematode is applied by watering onto moist soil, and gives protection for up to six weeks in optimum conditions, though is mainly effective with small and young slugs under the soil surface.

Plants to regulate insect pests

Choosing a diverse range of plants for the garden can help to regulate pests in a variety of ways, including;

  • Masking the crop plants from pests, depending on the proximity of the companion or intercrop.
  • Producing olfactory inhibitors, odors that confuse and deter pests.
  • Acting as trap plants by providing an alluring food that entices pests away from crops.
  • Serving as nursery plants, providing breeding grounds for beneficial insects.
  • Providing an alternative habitat, usually in a form of a shelterbelt, hedgerow, or beetle bank, where beneficial insects can live and reproduce. Nectar–rich plants that bloom for long periods are especially good, as many beneficials are nectivorous during the adult stage, but parasitic or predatory as larvae. A good example of this is the soldier beetle, which is frequently found on flowers as an adult, but whose larvae eat aphids, caterpillars, grasshopper eggs, and other beetles.

The following are plants often used in vegetable gardens to deter insects:

Plant Pests
Basil Repels flies and mosquitoes.
Catnip Deters flea beetle.
Garlic Deters Japanese beetle.
Horseradish Deters potato bugs.
Marigold The workhorse of pest deterrents. Discourages Mexican bean beetles, nematodes and others.
Mint Deters white cabbage moth, ants.
Nasturtium Deters aphids, squash bugs and striped pumpkin beetles.
Pot Marigold Deters asparagus beetles, tomato worm, and general garden pests.
Peppermint Repels the white cabbage butterfly.
Rosemary Deters cabbage moth, bean beetles and carrot fly.
Sage Deters cabbage moth and carrot fly.
Southernwood Deters cabbage moth.
Summer Savory Deters bean beetles.
Tansy Deters flying insects, Japanese beetles, striped cucumber beetles, squash bugs and ants.
Thyme Deters cabbage worm.
Wormwood Deters animals from garden.

Pathogens to be used as biopesticides

Various bacterial species are widely used in controlling the pests as well as weeds. The best–known bacterial biological control which can be introduced in order to control butterfly caterpillars is Bacillus thuringiensis, popularly called Bt. This is available in sachets of dried spores, which are mixed with water and sprayed onto vulnerable plants such as brassicas and fruit trees. After ingestion of the bacterial preparation, the endotoxin liberated and activated in the midgut will kill the caterpillars, but leave other insects unharmed. There are strains of Bt that are effective against other insect larvae. Bt. israelensis is effective against mosquito larvae and some midges.

Viruses most frequently considered for the control of insects (usually sawflies and Lepidoptera) are the occluded viruses, namely NPV, cytoplasmic polyhedrosis (CPV), granulosis (GV), and entomopox viruses (EPN). They do not infect vertebrates, non–arthropod invertebrates, microorganisms, and plants. The commercial use of virus insecticides has been limited by their high specificity and slow action.

Fungi are pathogenic agents to various organisms including the pests and the weeds. This feature is intensively used in biocontrol. The entomopathogenic fungi, like Metarhizium anisopliae, Beauveria bassiana, and so forth cause death to the host by the secretion of toxins. A biological control being developed for use in the treatment of plant disease is the fungus Trichoderma viride. This has been used against Dutch Elm disease, and to treat the spread of fungal and bacterial growth on tree wounds. It may also have potential as a means of combating silver leaf disease.

Significance of biological control

Biological control proves to be very successful economically, and even when the method has been less successful, it still produces a benefit–to–cost ratio of 11:1. The benefit–to–cost ratios for several successful biological controls have been found to range from 1:1 to 250:1. Further, net economic advantage for biological control without scouting vs. conventional insecticide control ranged from $ 7.43 to $ 0.12 per hectare in some places. It means that even if the yield produce under biological control be below that for insecticidal control by as much as 29.3 kilos per hectare, the biological control would not lose its economic advantage (CNR 2007).

Biological control agents are non–polluting and thus environmentally safe and acceptable. Usually they are species specific to targeted pest and weeds. The biological control discourages the use of environmentally and ecologically unsuitable chemicals, so it always leads to the establishment of natural balance. The problems of increased resistance in the pest will not arise, as both biological control agents and the pests are in complex race of evolutionary dynamism. Because of chemical resistance developed by the Colorado potato beetle (CPB), its control has been achieved by the use of bugs and beetles (Hein).

Negative results of biological control

Biological control tends to be naturally self–regulating, but as ecosystems are so complex, it is difficult to predict all the consequences of introducing a biological controlling agent (HP 2007). In some cases, biological pest control can have unforeseen negative results, that could outweigh all benefits. For example, when the mongoose was introduced to Hawaii in order to control the rat population, it predated on the endemic birds of Hawaii, especially their eggs, more often than it ate the rats. Similarly, the introduction of the cane toad to Australia 50 years ago to eradicate a beetle that was destroying sugar beet has been spreading as a pest throughout eastern and northern Australia at a rate of 35 km/22 mi a year. Since the cane toad is poisonous, it has few Australian predators to control its population (HP 2007).

  • CNR. 2007. Economics of biological control. College of Natural Resources, University of California, Berkeley. Retrieved December 7, 2007.
  • DigGood. Notes on natural pest control for an organic garden. DigGood.com. Retrieved December 7, 2007.
  • Hein, Gary L. Use of predators to control insect pests in potato. University of Nebraska–Lincoln. Retrieved December 7, 2007.
  • Hoddle, M. S., J. Grandgirard, J. Petit, G. K. Roderick, and N. Davies. 2006. Glassy-winged sharpshooter Ko’ed—First round—in French Polynesia. Biocontrol News and Information 27(3): 47N–62N
  • HP. 2007. Biological control. Helicon Publishing, Research Machines plc. Retrieved December 7, 2007.
  • Lawrence, L. 2005. Biocontrol: An overview of biological control research in CSIRO Entomology. CSIRO Australia. Retrieved December 7, 2007.
  • LUBILOSA. 2004 Biological control. GreenMuscle, Lubilosa, IITA Project A—Developing Biological Control Option. Retrieved December 7, 2007.
  • Metcalf, C. L., W. P. Flint, and R. L. Metcalf. 1973. Destructive and Useful Insects, Their Habitats, and Control. New Delhi: Tata McGraw–Hill Publishing Company.
  • Shanks, C. H., and F. Agudelo–Silva. 1990. Field pathogenicity and persistence of heterorhabditid and steinernematid nematodes (Nematoda) infecting black vine weevil larvae (Coteoptera: Curculionidae) in cranberry bogs. Journal of Economical Entomology 83: 107.
  • Smart, G. C. 1995. Entomopathogenic nematodes for the biological control of insects. Journal of Nematology 27(4S): 529–534.
  • UN–LN. 2003. Nematodes as biological control agents of insects. Plant and Insect Parasitic Nematodes. University of Nebraska–Lincoln Nematology. Retrieved December 7, 2007.
  • Weeden, C. R., A. M. Shelton, and M. P. Hoffman. 2007. Biological control: A guide to natural enemies in North America. Cornell University College of Agriculture and Life Sciences. Retrieved December 7, 2007.

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Biological control examples

Biological control example

An example of biological control is the release of parasitic wasps to control aphids. Aphids are a pest of plants and cause huge damage to plants as they remove nutrients from the plant.
The parasitic wasp lays eggs in aphids, as shown in the movie. The aphids will die when the eggs come out and the young wasps start to grow. In this way the aphid population will decrease quickly.
More information about the Biocomes approach to control Aphids is found here.

Entomopathogenic nematodes to control wine weevil

Heterorhabditis bacteriophora nematodes are used to control pests such as wine weevil; their control effect is helped by releasing bacteria into the soil which attack the wine weevil.


More information is found on the E-nema website.

Sclerotinia sclerotiorum controlled by fungal spores

Soil application of fungal spores of Coniothyrium minitans is used to destroy surviving structures of the common plant pathogen Sclerotinia sclerotiorum.
More information is found on the Bayer website.

Control of powdery mildew by Ampelomyces quisqualis

Another example of biological control is leaf application of fungal spores of Ampelomyces quisqualis to control mildew on greenhouse crops.


Powdery mildew on strawberry leaf. Picture: Elizabeth Bush, Virginia Polytechnic Institute and State University, Bugwood.org


AQ 10. Picture CBC Europe

More information is found on the Biogard/CBC europe website.

Codling moth killed by viruses

A spray with entomopathogenic viruses such as Cydia pomonella granulovirus (CpGV) is used to kill codling moths.
More information is found on the Andermatt Biocontrol website.

How to Manage Pests

Pests in Gardens and Landscapes

Biological Control and Natural Enemies of Invertebrates

Revised 12/14

In this Guideline:

  • Types of natural enemies
  • Recognizing natural enemies
  • Conservation: protect your natural enemies
  • Augmentation
  • Classical biological control or importation
  • Important links
  • About Pest Notes
  • Publication
  • Glossary

Adult convergent lady beetle feeding on aphids.

Parasitic wasp larvae visible through the surface of their scale insect host.

Aphid mummies and a parasitic wasp (Lysiphlebus testaceipes).

Biological control is the beneficial action of parasites, pathogens, and predators in managing pests and their damage. Biocontrol provided by these living organisms, collectively called “natural enemies,” is especially important for reducing the numbers of pest insects and mites. Use of natural enemies for biological control of rangeland and wildland weeds (e.g., Klamath weed, St. Johnswort) is also effective. Plant pathogens, nematodes, and vertebrates also have many natural enemies, but this biological control is often harder to recognize, less well understood, and/or more difficult to manage. Conservation, augmentation, and classical biological control are tactics for harnessing natural enemies’ benefits.

TYPES OF NATURAL ENEMIES

Parasites, pathogens, and predators are the primary groups used in biological control of insects and mites (Table 1). Most parasites and pathogens, and many predators, are highly specialized and attack a limited number of closely related pest species. Learn how to recognize natural enemies by consulting resources such as the Natural Enemies Handbook and the Natural Enemies Gallery.

Parasites

A parasite is an organism that lives and feeds in or on a host. Insect parasites can develop on the inside or outside of the host’s body. Often only the immature stage of the parasite feeds on the host. However, adult females of certain parasites (such as many wasps that attack scales and whiteflies) feed on and kill their hosts, providing an easily overlooked but important source of biological control in addition to the host mortality caused by parasitism.

Although the term “parasite” is used here, true parasites (e.g., fleas and ticks) do not typically kill their hosts. Species useful in biological control, and discussed here, kill their hosts; they are more precisely called “parasitoids.”

Most parasitic insects are either flies (Order Diptera) or wasps (Order Hymenoptera). Parasitic wasps occur in over three dozen Hymenoptera families. For example, Aphidiinae (a subfamily of Braconidae) attack aphids. Trichogrammatidae parasitize insect eggs. Aphelinidae, Encyrtidae, Eulophidae, and Ichneumonidae are other groups that parasitize insect pests. It’s important to note that these tiny to medium-sized wasps are incapable of stinging people. The most common parasitic flies are the typically hairy Tachinidae. Adult tachinids often resemble house flies. Their larvae are maggots that feed inside the host.

Pathogens

Natural enemy pathogens are microorganisms including certain bacteria, fungi, nematodes, protozoa, and viruses that can infect and kill the host. Populations of some aphids, caterpillars, mites, and other invertebrates are sometimes drastically reduced by naturally occurring pathogens, usually under conditions such as prolonged high humidity or dense pest populations. In addition to a naturally occurring disease outbreak (epizootic), some beneficial pathogens are commercially available as biological or microbial pesticides. These include Bacillus thuringiensis or Bt, entomopathogenic nematodes, and granulosis viruses. Additionally, some microorganism by-products, such as avermectins and spinosyns are used in certain insecticides; but applying these products is not considered to be biological control.

Predators

Predators kill and feed on several to many individual prey during their lifetimes. Many species of amphibians, birds, mammals, and reptiles prey extensively on insects. Predatory beetles, flies, lacewings, true bugs (Order Hemiptera), and wasps feed on various pest insects or mites. Most spiders feed entirely on insects. Predatory mites that feed primarily on pest spider mites include Amblyseius spp., Neoseiulus spp., and the western predatory mite, Galendromus occidentalis.

Table 1. Some Pests and Their Common Natural Enemies.

NATURAL ENEMIES
PESTS Lacewings Lady beetles Parasitic flies Parasitic wasps Predatory mites Other Groups and Examples
aphids X X X entomopathogenic fungi, soldier beetles, syrphid fly larvae
carpenterworm, clearwing moth larvae X entomopathogenic nematodes
caterpillars (e.g., California oakworm) X X X Bacillus thuringiensis, birds, entomopathogenic fungi and viruses, predaceous bugs and wasps, Trichogramma spp. (egg parasitic wasps), spiders
cottony cushion scale X X Cryptochaetum iceryae (parasitic fly), vedalia beetle
elm leaf beetle X X Erynniopsis antennata (parasitic fly), Oomyzus (=Tetrastichus) spp. (parasitic wasps)
eucalyptus longhorned borers X Avetianella longoi (egg parasitic wasp)
eucalyptus redgum lerp psyllid X Psyllaephagus bliteus (parasitic wasp)
giant whitefly X X X Encarsia hispida, Encarsia noyesi, Entedononecremnus krauteri, and Idioporus affinis (parasitic wasp), syrphid fly larvae
glassy-winged sharpshooter X X assassin bugs, Gonatocerus spp. (egg parasitic wasps), spiders
lace bugs X X X assassin bugs and pirate bugs, spiders
mealybugs X X X mealybug destroyer lady beetle
mosquitoes Bacillus thuringiensis spp. israelensis, mosquito-eating fish
psyllids X X X pirate bugs
scales X X X X Aphytis, Coccophagus, Encarsia, and Metaphycus spp. parasitic wasps
slugs, snails X Rumina decollata (predatory snail), predaceous ground beetles, birds, snakes, toads, and other vertebrates
spider mites X X X bigeyed bugs and minute pirate bugs, Feltiella spp. (predatory cecidomyiid fly larvae), sixspotted thrips, Stethorus picipes (spider mite destroyer lady beetle)
thrips X X X minute pirate bugs, predatory thrips
weevils, root or soil-dwelling X Steinernema carpocapsae and Heterorhabditis bacteriophora (entomopathogenic nematodes)
whiteflies X X X bigeyed bugs and minute pirate bugs, Cales, Encarsia, and Eretmocerus spp. parasitic wasps, spiders

Green lacewing larva attacking aphid with its mandibles.

Adult assassin bug attacking a lygus bug.

Entomopathogenic nematodes emerging from a root weevil larva they killed.

Table 2. Some Important Parasites of Insects.

Anaphes species

Aphidius species

Aphytis spp., armored scale parasites

Bracon cushmani, grape leaffolder parasite

Citrus mealybug parasite

Cotesia medicaginis, alfalfa butterfly parasite

Cottony cushion scale parasite

Elm leaf beetle parasite

Encarsia formosa, whitefly parasite

Hyposoter exiguae, caterpillar parasite

Lysiphlebus testaceipes, aphid parasite

Tachinid flies

Trichogramma spp., egg parasites

Trioxys pallidus, walnut aphid parasite

RECOGNIZING NATURAL ENEMIES

Proper identification of pests, and distinguishing pests from natural enemies, is essential for effective biological control. Carefully observe the mites and insects on your plants to help discern their activity. For example, some people may mistake syrphid fly larvae for caterpillars. However, syrphid fly larvae are found feeding on aphids and not chewing on the plant itself. If you find mites on your plants, observe them with a good hand lens. Predaceous mites appear more active than plant-feeding species. In comparison with pest mites, predaceous mites are often larger and do not occur in large groups.

Consult publications listed in the References to learn more about the specific pests and their natural enemies in your gardens and landscapes. Take unfamiliar organisms you find to your local University of California (UC) Cooperative Extension office, UC Master Gardener Program, or agricultural commissioner office in your county for aid in identification.

CONSERVATION: PROTECT NATURAL ENEMIES

Preserve existing natural enemies by choosing cultural, mechanical, or selective chemical controls that do not harm beneficial species. Remember, only about 1% of all insects and mites are harmful. Most pests are attacked by multiple species of natural enemies (Table 1), and their conservation is the primary way to successfully use biological control. Judicious (e.g., selective, timing) pesticide use, ant control, and habitat manipulation are key conservation strategies.

Pesticide Management

Biological control’s importance often becomes apparent when broad-spectrum, residual pesticides (those that persist for days or weeks) cause secondary pest outbreaks or pest resurgence. An example is the dramatic increase in spider mite populations (flaring) that sometimes results after applying a carbamate (e.g., carbaryl or Sevin) or organophosphate (malathion) to control caterpillars or other insects.

Eliminate or reduce the use of broad-spectrum, persistent pesticides whenever possible. Carbamates, organophosphates, and pyrethroids kill natural enemies that are present at the time of spraying and for days or weeks afterwards their residues kill predators and parasites that migrate in after spraying. Neonicotinoids (e.g., dinetofuran, imidacloprid) and other systemic insecticides that translocate (move) into blossoms can poison natural enemies and honey bees that feed on nectar and pollen. Even if beneficials survive an application, low levels of pesticide residues can interfere with natural enemies’ reproduction and their ability to locate and kill pests.

When pesticides are used, apply them in a selective manner. Treat only heavily infested areas with “spot” applications instead of entire plants. Choose insecticides that are more specific in the types of invertebrates they kill, such as Bacillus thuringiensis (Bt) that kills only caterpillars that consume treated foliage.

For most other types of exposed-feeding insects, rely on contact insecticides with little or no persistence, including azadirachtin, insecticidal soap, narrow-range oil (horticultural oil), neem oil, and pyrethrins, which are often combined with the synergist piperonyl butoxide.

In situations where you wish to foster biological control, use of nonpersistent pesticides can provide better long-term control of the pest because they do less harm to natural enemies that migrate in after the application. To obtain adequate control, thoroughly wet the infested plant parts with spray beginning in spring when pests become abundant. To provide sustained control, repeated application may be needed.

For certain harder-to-control pests where contact-only insecticides are inadequate, other choices include spinosad, a fermentation product of a naturally occurring bacterium. This insecticide persists about 1 week and it has translaminar activity (is absorbed short distances into plant tissue). Spinosad can be toxic to certain natural enemies (e.g., predatory mites, Trichogramma wasps, and syrphid fly larvae) and bees when sprayed and for about 1−4 days afterwards; do not apply spinosad to plants that are flowering.

Relative toxicity of insecticides to natural enemies.

TOXICITY TO PARASITES AND PREDATORS1
INSECTICIDE Direct Residual
microbial (Bacillus thuringiensis) no no
botanicals (pyrethrins) yes/no2 no
oil (horticultural), soap (potash soap) yes no
microbial (spinosad) yes/no2 yes/no2
neonicotinoids (imidacloprid) yes/no2 yes
carbamates (carbaryl), organophosphates (malathion), pyrethroids (bifenthrin) yes yes

1. Direct contact toxicity is killing within several hours from spraying the beneficial or its habitat. Residual toxicity is killing or sublethal effects (such as reduced reproduction or ability to locate and kill pests) due to residues that persist.

2. Toxicity depends on the specific material and how it is applied and the species and life stage of the natural enemy.

See the active ingredients database for more information about specific pesticides.

Ant Control and Honeydew Producers

The Argentine ant and certain other ant species are considered pests primarily because they feed on honeydew produced by insects that suck phloem sap, such as aphids, mealybugs, soft scales, psyllids, and whiteflies. Ants protect honeydew producers from predators and parasites that might otherwise control them. Ants sometimes move these honeydew-producing insects from plant to plant (called “farming”). Where natural enemies are present, if ants are controlled, populations of many pests will gradually (over several generations of pests) be reduced as natural enemies become more abundant. Control methods include cultivating soil around ant nests, encircling trunks with ant barriers of sticky material, and applying insecticide baits near plants. See Pest Notes: Ants for more information.

Habitat Manipulation

Plant a variety of species that flower at different times to provide natural enemies with nectar, pollen, and shelter throughout the growing season. The adult stage of many insects with predaceous larvae (such as green lacewings and syrphid flies) and many adult parasites feed only on pollen and nectar. Even if pests are abundant for the predaceous and parasitic stages, many beneficials will do poorly unless flowering and nectar-producing plants are available to supplement their diet. To retain predators and parasites, grow diverse plant species well adapted to the local conditions and that tolerate low populations of plant-feeding insects and mites so that some food is always available.

Other cultural controls that can help natural enemies include reducing dust and properly fertilizing and irrigating. Dust can interfere with natural enemies and may cause outbreaks of pests such as spider mites. Reduce dust by planting ground covers and windbreaks and hosing off small plants that become excessively covered with dust. Avoid excess fertilization and irrigation, which can cause phloem-feeding pests, such as aphids, to reproduce more rapidly than natural enemies can provide control.

AUGMENTATION

When resident natural enemies are insufficient, their populations can sometimes be increased (augmented) through the purchase and release of commercially available beneficial species. However, there has been relatively little research on releasing natural enemies in gardens and landscapes. Releases are unlikely to provide satisfactory pest control in most situations. Some marketed natural enemies are not effective. Many natural enemies are generalist predators and are cannibalistic and feed indiscriminately on pest and beneficial species, thereby reducing their effectiveness.

Only a few natural enemies can be effectively augmented in gardens and landscapes. For example, entomopathogenic nematodes can be applied to control certain tree-boring and lawn-feeding insects. Convergent lady beetles (Hippodamia convergens) purchased in bulk through mail order, stored in a refrigerator, and released in very large numbers at intervals can temporarily control aphids; however, lady beetles purchased through retail outlets are unlikely to be sufficient in numbers and quality to provide control.

Successful augmentation generally requires advanced planning, biological expertise, careful monitoring, optimal release timing, patience, and situations where certain levels of pests and damage can be tolerated. Situations where pests or damage are already abundant are not good opportunities for augmentation.

CLASSICAL BIOLOGICAL CONTROL OR IMPORTATION

Classical biological control, also called importation, is primarily used against exotic pests that have inadvertently been introduced from elsewhere. Many organisms that are not pests in their native habitat become unusually abundant after colonizing new locations without their natural controls. Researchers go to the pest’s native habitat, study and collect the natural enemies that kill the pest there, then ship promising natural enemies back for testing and possible release. Many insects and some weeds that were widespread pests in California are now partially or completely controlled by introduced natural enemies, except where these natural enemies are disrupted, such as by pesticide applications or honeydew-seeking ants.

By law, natural enemy importation must be done only by qualified scientists with government permits. Natural enemies are held and studied in an approved quarantine facility to prevent their escape until research confirms that the natural enemy will have minimal negative impact in the new country of release.

It is important for landscape managers to recognize imported natural enemies and conserve them whenever possible. Because classical biological control can provide long-term benefits over a large area and is conducted by agencies and institutions funded through taxes, public support is critical to the continued success of classical biological control.

Is Biological Control “Safe”?

A great benefit of biological control is its relative safety for human health and the environment, compared to widespread use of broad-spectrum pesticides. Most negative impacts from exotic species have been caused by undesirable organisms contaminating imported goods, by travelers carrying in pest-infested fruit, and from introduced ornamentals that escape cultivation and become weeds. These ill-advised or illegal importations are not part of biological control.

Negative impacts have occurred from poorly conceived, quasi-biological control importations of predaceous vertebrates like frogs, mongooses, and certain fish, often conducted by nonscientists. To avoid these problems, biological control researchers follow government quarantine regulations and work mostly with host-specific natural enemies that pose low risks and can provide great benefits. As a pest comes under biological control, population densities decline for both the pest and the biological control agent because host-specific natural enemies cannot prey or reproduce on other species.

WARNING ON THE USE OF PESTICIDES

Rust, M.K. and D.-H. Choe. 2012. Pest Notes: Ants. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 7411.

IMPORTANT LINKS

Quick Tip Beneficial Predators

Quick Tip Common Garden Spiders

Quick Tip Lady Beetles

Quick Tip Parasites of Insect Pests

Natural Enemies Gallery

Narrated presentation on biological control (24 minutes)

More biological control resources

PUBLICATION INFORMATION

Pest Notes: Biological Control and Natural Enemies of Invertebrates

UC ANR Publication 74140

Author: S. H. Dreistadt, UC Statewide IPM Program, Davis

Produced by University of California Statewide IPM Program

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Spring is on the way!

Now that most parts of the country are slowly inching out of winter and into spring, you may be thinking about your garden. Beneficial nematodes are a great, natural alternative for insect pest control. Perhaps you are interested in buying nematodes, or have already purchased them to use to defend your spring plants; so, when can you apply them? It is true that beneficial nematodes are temperature sensitive, so proper (and timely) application is critical.

The ideal time to apply nematodes is dependent on a number of factors including the type of nematode (BioLogic sells 3 different species of nematodes), the pest(s) being targeted and soil conditions. In general, you can apply nematodes in early spring once the soil is no longer frozen. We recommend applying at dusk, to protect the nematodes from UV light and drying out. Water the area to be treated well both before and after nematode application. Also, be sure to keep nematodes refrigerated until you are ready to use them, and apply by the “use by” date.

We are excited to get out and garden, and hope you are too!

How to Apply Nematodes to Control Grubs

For any lawn enthusiast the white grub is public enemy #1! The brown patches they leave on your lawn are an eyesore that are just ugly. Fight grubs naturally with beneficial nematodes, naturally occurring microscopic worms that prey on grubs. An enemy of my enemy is my friend!

What Are They?

Beneficial Nematodes are a naturally occurring microscopic worm found around the globe in soils. Nematodes hunt and feed on soil dwelling insects by entering their body, injecting them with lethal bacteria, and feeding from their insides. The toxin usually kills the host insect within a day or two. To complete the lifecycle, they also lay their offspring in the dead grub (or other pest). There are different kinds of nematodes for targeting different turf insects, but we carry the nematodes that go after grubs!

Keeping & Using Nematodes

Nematodes are super easy to use, require very little work and no sprays! You get a whopping 10 million nematodes in an individual package. That will cover an area between 2000-3000 square feet (based on a heavy or light application rate). They are shipped in a powdery solution that mixes well in water. Be sure to keep your nematodes in the fridge (but not frozen) and apply as soon as possible for best results. They are a living insect so the longer you wait the less effective they will be (they can die if you wait too long). Do not use nematodes at are past their expiration date. You can apply them using a watering can, sprayer and hose attachment or misting system. It’s a good idea to apply your nematodes during low light periods (morning or evening are best).

It is very important that you mix and apply your nematodes quickly so they don’t ‘expire’ in the can. You want to insure the nematodes have a chance to get into the soil before the water is evaporated. If possible, you should water your lawn or apply after a light rain for best penetration. Avoid applying to over-saturated soil as nematodes will simply wash away and avoid applications when your soil temperature is below 10°C / 50°F if you’re using local, Canadian grown nematodes (15°C / 60°F for imported nematodes).

Using a hose end sprayer applicator will be applying nematodes very easy, just mix a concentration, fill your applicator and spray out nematodes until the jar is empty. Refill applicator until all your concentrated nematode solution has been applied. If you have an applicator which refills your jar as you spray mix a tea bag in with your nematode concentration. This will turn your concentration a tea colour and when the concentration is diluted clear you know you’ve run out of nematodes.

There are two periods when grubs can be targeted by nematodes, in the spring when soil temperatures are above 10°C (often early May to early June) and again in the fall before soil gets too cold (mid-late September to mid October). During those times the insects are in a life cycle where grubs are in the soil and can be targeted. The best time is in the fall when the grubs are smaller but the most common time is in the spring. Best practice is applying during both to get best coverage and protection!

Lastly, always read the expiry date and apply before they go bad because dead nematodes don’t work and it’s very hard to see if they are alive or not. Don’t chance it, deal with them right away.

Application Video

There is a great video that shows how to apply nematodes using a hose end sprayer that is available at Heeman’s. You can watch this video here.

Integrated Pest Management IPM

NATURAL PEST CONTROL WITH BENEFICIAL NEMATODES

Biological Control Of Pest Insects With Nematodes. Beneficial Nematodes naturally occur in soil and are used to control soil pest insects and whenever larvae or grubs are present. Like all of our products, it will not expose humans or animals to any health or environmental risks. Beneficial nematodes only attack soil dwelling insects and leave plants and earthworms alone. The beneficial nematodes enters the larva via mouth, anus or respiratory openings and starts to feed. This causes specific bacteria to emerge from the intestinal tract of the nematode. These spread inside the insect and multiply very rapidly. The bacteria convert host tissue into products which can easily be taken up by the nematodes. The soil dwelling insect dies within a few days. Beneficial nematodes are a totally safe biological control in pest insects. The Beneficial nematodes are so safe the EPA has waived the registration requirements for application.

NATURE’S BEST WAY OF KILLING Grubs and Japanese Beetles. We ship Beneficial Nematodes to USA and Canada. For USA visit our website: www.buglogical.com or call 520-298-4400 for more information. Though they are harmless to humans, animals, plants, and healthy earthworms, beneficial nematodes aggressively pursue insects. The beneficial nematodes can be used to control a broad range of soil inhabiting insects and above ground insects in their soil inhabiting stage of life. More than 200 species of pest insects from 100 insect families are susceptible to these nematodes. When they sense the temperature and carbon dioxide emissions of soil-borne insects, beneficial nematodes move toward their prey and enter the pest through its body openings. The nematodes carry an associated bacterium (Xenorhabdus species) that kills insects fast within 48 hours. The bacteria is harmless to humans and other organisms and cannot live freely in nature. Several generations of nematodes may live and breed within the dead insect, feeding on it as a food source. When the food source is gone, they migrate into the soil in search of a new host. When the pest population is eliminated, the beneficial nematodes die off and biodegrade. Beneficial nematodes are so effective, they can work in the soil to kill the immature stages of garden pests before they become adults.,

Beneficial nematodes infest grubs and other pest insects that are known to destroy lawns and plants.

The Nematodes are effective against grubs and the larval or grub stage of Japanese Beetles, Northern Masked Chafer, European Chafer, Rose Chafer, Fly larvae, Oriental Beetles, June Beetles, Flea beetles, Bill-bugs, Cut-worms, Army worms, Black Vine Weevils, Strawberry Root Weevils, Fungus Gnats, Sciarid larvae, Sod Web-worms, Girdler, Citrus Weevils, Maggots and other Dip-tera, Mole Crickets, Iris Borer, Root Maggot, Cabbage Root Maggot and Carrot Weevils. Beneficial nematodes belong to one of two genera: Steinernema and Heterorhabditis are commercially available in the U.S. Steinernema is the most widely studied beneficial nematode because it is easy to produce. Heterorhabditis is more difficult to produce but can be more effective against certain insects, such as the white grubs, and Japanese beetles. How beneficial nematodes work: The life cycle of beneficial nematodes consists of six distinct stages: an egg stage, four juvenile stages and the adult stage. The adult spends its life inside the host insect. The third juvenile stage, called a dauer, enters the bodies of insects (usually the soil dwelling larval form. Some nematodes seek out their hosts, while others wait for the insect to come to them. Host seeking nematodes travel through the soil the thin film of water that coats soil particles. They search for insect larvae using built-in homing mechanisms that respond to changes in carbon dioxide levels and temperature. They also follow trails of insect excrement. After a single nematode finds and enters an insect through its skin or natural openings, the nematode release a toxic bacteria that kills its host, usually within a day or two. In less than two weeks the nematodes pass through several generations of adults, which literally fill the insect cadaver. Steinernema reproduction requires at least two dauer nematodes to enter an insect, but a single Heterorhabditis can generate offspring on its own. The nematodes actively searches for insect larvae. Once inside the larva the nematodes excretes specific bacteria from its digestive trac before it starts to feed. The bacteria multiply very rapid and convert the host tissue into products that the nematodes take up and use for food. The larva dies within a few days and the color changes from white-beige to orange-red or red-brown. The nematodes multiply and develop within the dead insect. As soon as the nematodes are in the infectious third stage, they leave the old host and start searching for new larvae. Infected grubs turn color from white-beige to red brown 2-4 days after application and becomes slimy. After a few weeks, dead larvae disintegrate completely and are difficult to find. Beneficial nematodes are also very effective against termites, German cockroaches, flies, ant, and fleas.

APPLICATION:

Beneficial Nematodes are very easy to use. Mix with water and spray or sprinkle on the soil along garden plants or lawn. Put the contents of the Beneficial nematodes in a bucket of water and stir to break up any lumps, and let the entire solution soak for a few minutes. Application can be made using a water-can, irrigation system, knapsack or sprayer. On sprayer use a maximum pressure to avoid blockage, all sieves should be removed. The sprayer nozzle opening should be at least 1/2 mm. Evenly spread the spraying solutions over the ground area to be treated. Continuous mixing should take place to prevent the nematodes from sinking to the bottom. After application keep the soil moist during the first two weeks for the nematodes to get establish. For a small garden the best method is using a simple sprinkling or water can to apply the Beneficial nematodes to the soil. Apply nematodes before setting out transplants; for other pest insects, Japanese Beetles and grubs, apply whenever symptomatic damage from insects is detected. Best to apply water first if soil is dry.Application and amount for 50 and 100 Mil. Nematodes. The 50 Mil. + nematodes are packed in an inert carrying material that will dissolve in water when mixed. You can use a watering can, pump sprayer; hose end sprayer and irrigation system, backpack sprayers, or motorized sprayer. The 10 Mil. 50 Mil. and 100 Mil. Nematodes mix 1 teaspoon per gallon of water. The Large yard size: 1/2 Acre Size (50 Million) you can use up to 40 Gallons of water The Acre size 100 Mil. Nematodes you can use up to 100 Gallons of water. Evenly spread the solution over the ground areas to be treated. Continuous mixing should take place to prevent the nematodes from sinking to the bottom of the container. To avoid blockages, remove all filters from the sprayer. You can sprinkle the soil with water again after application to move the nematodes into the soil. Apply nematodes as soon as possible for best product performance. Keep the soil most for the first week after application.

Proper storage and handling is essential to nematode health.

Always follow the package instructions for the best method of mixing nematodes. Formulations vary depending on the species and target insect. Nematodes can be stored in the refrigerator up to a month (not the freezer) before they are mixed with water, but once the nematodes are diluted in water, they cannot be stored. Also, nematodes shouldn’t be stored in hot vehicles, or left in spray tanks for long periods of time.Nematodes need moisture in the soil for movement (if the soil is too dry or compact, they may not able to search out hosts) and high humidity if they are used against foliage pests. Watering the insect-infested area before and after applying nematodes keeps the soil moist and helps move them deeper into the soil. Care should be taken not to soak the area because nematodes in too much water cannot infect. Exposure to UV light or very high temperatures can kill nematodes. Apply nematodes in the early evening or late afternoon when soil temps are lower and UV incidence is lower as well (cloudy or rainy days are good too). Nematodes function best with soil temperatures between 48Fº and 93Fº day time temperatures.

Application is usually easy.

In most cases, there is no need for special application equipment. Most nematodes species are compatible with pressurized, mist, electrostatic, fan and aerial sprayers! Hose-end sprayers, pump sprayers, and watering cans are effective applicators as well. Nematodes are even applied through irrigation systems on some crops. Check the label of the nematode species to use the best application method. Repeat applications if the insect is in the soil for a longer period of time. There is no need for masks or specialized safety equipment. Insect parasitic nematodes are safe for plants and animals (worms, birds, pets, children). Because they leave no residues, application can be made anytime before a harvest and there is no re-entry time after application. How to use beneficial nematodes: For the home gardener, localized spraying is probably the quickest and easiest way to get the nematodes into the soil. Producers ship beneficial nematodes in the form of dry granules, powder type clay, and sponges. All of these dissolve in water and release the millions of nematodes. Each nematode ready to start searching for an insect in your lawn or garden. Nematodes should be sprayed on infested areas at the time when pests is in the soil. Timing is important, or else you will have to repeat the application. Northern gardeners should apply the nematodes in the spring, summer and fall, when the soil contains insect larvae. Most of the beneficial nematodes are adaptive to cold weather. In fact , the very best time to control white grubs is in the spring and fall. If your in a warmer climate, beneficial nematodes are effective all year.

Fertilizers should be avoided roughly 2 weeks prior to and after nematode application, because they may be adversely affected by high nitrogen content.

Some pesticides work well with nematodes when their mutual exposure is limited while other pesticides may kill nematodes. Check labels or specific fact sheets to find out. Some chemicals to avoid are bendiocarb, chlorpyrifos, ethoprop, and isazophos. Fungicides to avoid are anilazine, dimethyl benzyl, ammonium chloride, fenarimol, and mercurous chloride. The herbicides, 2,4-D and trichlopyr and nematicide, fenamiphos, should be avoided as well. During hot weather release nematodes in the evening or afternoon when temperature is cooler. Release once or twice a year or until infestation subsides. Nematodes are shipped in the infectious larvae stage of their life cycle and can be stored in the refrigerator for up to 4 weeks. Always release very early in the morning or late in the late afternoon.

Why are these organisms beneficial?

Beneficial nematodes seek out and kill all stages of harmful soil-dwelling insects. They can be used to control a broad range of soil-inhabiting insects and above-ground insects in their soil-inhabiting stage of life.

Parasitic nematodes are beneficial for eliminating pest insects. First, they have such a wide host range that they can be used successfully on numerous insect pests. The nematodes’ nonspecific development, which does not rely on specific host nutrients, allows them to infect a large number of insect species. Nematodes enter pest bugs while they are still alive, then they multiply inside the bugs (which eventually die) and finally burst out of the dead bodies. The number of nematodes inside a single bug (depending on the species) ranges from 5,000 to 10,000. Although you can barely see one young nematode with your naked eye, large groups of these tiny wigglers pouring out of the dead insects are easy to see. Then the nematodes wriggle off to find other insects to “invade,” starting the whole cycle all over again. Second, nematodes kill their insect hosts within 48 hours. As mentioned earlier, this is due to enzymes produced by the Xenorhabdus bacteria. Also, the infective juveniles can live for some time without nourishment as they search for a host. Finally, there is no evidence that parasitic nematodes or their symbiotic bacteria can develop in vertebrates. This makes nematode use for insect pest control safe and environmentally friendly. The United States Environmental Protection Agency (EPA) has ruled that nematodes are exempt from registration because they occur naturally and require no genetic modification by man. Beneficial nematodes can be an excellent tool in the lawn and garden to control certain pest insects. They can be used with organic gardening and are safe for kids and pets.

Description

What is a nematode? Nematodes are microscopic, whitish to transparent, unsegmented worms. They occupy almost every conceivable habitat on earth, both aquatic and terrestrial, and are among the most common multicelled organisms. Nematodes are generally wormlike and cylindrical in shape, often tapering at the head and tail ends; they are sometimes called roundworms or eelworms. There are thousands of kinds of nematodes, each with their particular feeding behavior — for example, bacterial feeders, plant feeders, animal parasites, and insect parasites, to name a few.

Insect-Parasitic Nematodes. Traditionally, soil-inhabiting insect pests are managed by applying pesticides to the soil or by using cultural practices, for example, tillage and crop rotation. Biological control can be another important way to manage soil-inhabiting insect pests. A group of organisms that shows promise as biological control agents for soil pests are insect-parasitic nematodes. These organisms, which belong to the families Steinernematidae and Heterorhabditidae, have been studied extensively as biological control agents for soil-dwelling stages of insect pests. These nematodes occur naturally in soil and possess a durable, motile infective stage that can actively seek out and infect a broad range of insects, but they do not infect birds or mammals. Because of these attributes, as well as their ease of mass production and exemption from EPA registration, a number of commercial enterprises produce these nematodes as biological “insecticides.”

How to order Beneficial Nematodes: All nematodes are not the same. Buglogical nematodes are more tolerant of high tempertures than any other brands. It is best to order biological control nematodes and have them delivered directly to you from a reliable source.. This helps insure that the nematodes you are buying are still alive. Nematodes do not live very long in storage. Therefore, buying nematodes that are stocked on a store shelf is very risky.

Suppliers: Buglogical Control Systems, Inc. PO Box 32046, Tucson, AZ 85751-2046 Phone: 520-298-4400

www.buglogical.com

Georgis, R. and G.O. Poinar. 1989. Field Effectiveness of Entomophilic Nematodes Neoaplectana andHeterorhabditis.Pages 213-224, In A.R. Leslie and R.L. Metcalf (eds.). Integrated Pest Management for Turfgrass and Ornamentals.United States Environmental Protection Agency, Washington, DC.

Shetlar, D.J. 1989. Entomogenous Nematodes for Control of Turfgrass Insects with Notes on Other Biological Control Agents.Pages 225-253, InA.R. Leslie and R.L. Metcalf (eds.) Integrated Pest Management for Turfgrasses and Ornamentals. United States Environmental Protection Agency, Washington, DC.

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