Biological pest control, also known as biological control or biocontrol, is an aspect of integrated pest management strategy which is not often used. It is an excellent alternative to chemical methods of controlling pest infestation.

Biological pest control is a method of suppressing pest populations by introducing their natural enemies, referred to as biological control agents. The biological agents can be encouraged to develop within the pest-invested system or artificially introduced.

These pests do not only include insects and mites, but also diseases and weeds in a crop plantation. If you’re curious about the biological control of insects, weeds, and plant diseases, read on!

What is biological pest control

There are three types of biological control:

1. Conservation biocontrol

This involves the conservation of existing natural enemies within the infested system. It is probably the most important and readily available biological control practice available to homeowners and gardeners.

How this method works

Natural enemies occur in all areas, from the backyard garden to the commercial field. They are always readily adapted to the local environment and to the target pest. Conserving them is also simple and cost-effective.

For example, a snake is a biological control agent that consumes a lot of rodent and insect pests that can be damaging to agricultural crops or spread disease. Also, Dragonflies are important consumers of mosquitoes.

Eggs, larvae, and pupae of Helicoverpa moths, the main insect pests of cotton, are also attacked by many beneficial insects. These naturally occurring biological control agents are often susceptible to the same pesticides used to target their prey.

Preventing the accidental eradication of natural enemies is the way to carry out conservative biological pest control.

2. Classical biological control

This is the introduction of exotic natural enemies to a new location where they did not actually originate or occur naturally. This is usually carried out by government authorities.

When the complex of natural enemies that can eradicate an insect pest is inadequate, additional biological agents can be introduced. Also, when an insect pest is accidentally introduced into a new geographic area without its associated natural enemies, the introduced pests are referred to as exotic pests and there’s a need to introduce the associated natural enemies.

How this method works

To obtain the needed natural enemies, scientists have utilized classical biological control. This is the practice of importing and releasing natural enemies to control an introduced (exotic) pest. It can also be practiced against native insect pests as explained above. 

  • The first step in the classical biocontrol process is to determine the origin of the exotic pest. The pest control experts will then collect appropriate natural enemies associated with the pest or its closely related species. The natural enemy will be made to pass through a rigorous quarantine process, to ensure that no unwanted organisms (such as hyperparasitoids or parasites of the parasite) are introduced.
  • The final step is to produce the biocontrol agent in large amounts and they will then be released 
  • Follow–up studies are conducted to determine if the natural enemy becomes successfully established at the site of release. Assessment of the long–term benefit of its presence against the pest will then be carried out. 

Examples of introduced vegetable pests include the European corn borer, one of the most destructive insects in North America. 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 underway across the United States and Canada.

Is classical biological control reliable?

Classical biological control is a long-lasting intervention and it is not expensive. Other than the initial costs of collection, importation, and rearing, little expense is incurred. When a natural enemy is successfully established, it mostly does not require any additional input and it continues to kill the pest with no direct help from humans.

However, classical biological control does not always work. It is usually most effective against exotic pests and less so against native insect pests. The exact reasons for failure are not yet known. The release of too few individuals or poor adaptation of the natural enemy to the new environmental conditions are some of the factors that may be responsible for its failure.

3. Augmentative biological control

This is another biocontrol strategy that involves the supplemental release of natural enemies. Very few natural enemies may be released at a critical time of the season and this is known as inoculative release.

Millions of natural enemies may also be released and this is known as inundative release. In addition to the release, there will be habitat manipulation where the cropping is also being modified to favor or augment the natural enemies.

An example of inoculative release occurs in the 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 usually 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 the level of pest infestation.

How this method works

Habitat or environmental manipulation is an additional form of augmentation. This method 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 refugees 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 can be easily incorporated into home gardens and even small-scale commercial plantings. Habitat manipulation may be more difficult to carry out in large–scale crop production.

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

Biological control experts in California have demonstrated that planting prune trees in grape vineyards provide 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.

One great side effect of this method is that 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 method has proved promising from previous research works.

Advantages of biological pest control

Advantages of Biological pest control

Minimized safety concerns

Unlike chemical pesticides, biological pest control minimizes environmental, legal, and public safety concerns. The biocontrol agents do not leave behind long-lasting residues that can be toxic to the environment. They don’t leach into groundwater or create resistant strains of insects.

Increased selectivity

The biocontrol method is often a host-parasite or prey-predator relationship which is usually specific and doesn’t affect other organisms. This is a great benefit to the environment as it doesn’t interfere with other natural processes. For instance, when using nematodes for insect control, it’s important to use the correct species for the insect you want to control.

Biological-control nematodes aren’t parasitic on their host. They enter the insect through a natural body opening and then eat the bacteria they carry with them that multiply inside the host. Nematodes have to be the right size to enter the particular insect and must have behavior that allows contact with the insect to begin with.

Cost considerations

Biological control is usually less expensive compared to pesticides. You can incur significant expenses studying, choosing, testing, and breeding a bioagent, However, the actual cost of deploying is mostly insignificant and they can be used in more than one location.

Also, in cases where bioagents are applied to low-level pest populations, pest control can be long-term and inexpensive. Some fungi attack insects and kill them. A fungal spore penetrates the insect and grows throughout it. It takes about a week for the insect to die. Fungi biocontrols are cost-effective unless a high application rate is needed for heavy insect infestations.

Disadvantages of biological pest control

Time demanding

Bioagents may take several generations or more before they can successfully manage pest populations. For instance, the imported fire ant, a serious pest in the southern United States, is parasitized by a tiny phorid fly native to its South American range.

When the phorid fly is bred and released into the imported fire ant’s U.S. range, less than 3 to 4 percent of the ants in a colony become infected. The effect of phorid flies on imported fire ant colonies could take years to become evident.

Skill requirement

Biological pest control strategies require professional intervention. It may be more difficult for a nonprofessional to accomplish biological control due to the several variables involved. The specialized knowledge of pests, bioagents, and environmental conditions is often needed for success.

Risk of new pests invasion

When a non-native bioagent is introduced to control a non-native pest species, it sometimes becomes a pest itself. For example, the multicolored Asian lady beetle was introduced into the United States to control aphids. It became a pest insect that invades homes for overwintering.

In Hawaii, the small Indian mongoose was introduced to control snakes and rats in sugarcane fields. It also preys on native Hawaiian birds, amphibians, reptiles, and poultry.

Types of biological control agents

Predators

1. Ladybug

The adult and larvae of Ladybugs are active between May and July in the northern hemisphere and they are voracious predators of aphids such as greenfly and blackfly. It will also consume mites, scale insects, and small caterpillars. The ladybug is a very familiar beetle with various colored markings.

The Ladybug larvae are initially small and spidery, growing up to 17 millimeters long. They have a tapering segmented gray/black body with orange or yellow markings.

2. Hoverflies

Hoverflies are similar to darker bees or wasps. They have characteristic hovering, and darting flight patterns. There are over 100 species of hoverfly, whose larvae principally feed upon greenflies, one larva devouring up to 50 a day or 1000 in its lifetime. They also eat fruit tree spider mites and small caterpillars.

Adult hoverflies feed on nectar and pollen which helps them with egg production. Their eggs are minute, 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.

Hoverflies can be multiplied by growing attractant flowers such as the poached eggplant (Limnanthes douglasii), marigolds, or phacelia throughout the growing season.

3. Dragonflies

Dragonflies are important predators of mosquitoes, both in the water and in the air. The dragonfly naiads eat mosquito larvae in the water while adult dragonflies capture and eat adult mosquitoes in the air.

Community-wide mosquito control programs that spray adult mosquitoes make the mistake of also killing dragonflies, thus removing an important biocontrol agent. This will actually increase mosquito populations in the long term.

4. Other garden predators

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 pests animals as well. Dachshunds are bred specifically to fit inside tunnels underground to kill badgers.

Parasitoidal insects

Most insect parasitoids are wasps or flies. 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, since 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.

The most important groups are Ichneumonid wasps, Braconid wasps, Chalcid wasps, and Tachinid flies.

Parasitic nematodes

Nine families of nematodes include species that attack insects and kill or sterilize them or alter their development. In addition to insects, nematodes can parasitize spiders, leeches, annelids, 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 cranberries are restricted.

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Ben McInerney
Author: Ben McInerney - Ben is a qualified arborist with 15 plus years of industry experience in Arboriculture. He ran a successful tree service before turning to writing and publishing. Ben is dedicated to providing users with the most accurate up-to-date information on everything trees.