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Biological control agents and examples: What are the different types?

Theme: Biocontrol agents


Understanding the range of biocontrol agents and how they interact with the target pest aids in selecting a suitable agent for your production system. It also gives insight into more effective utilization. Here we provide additional information and resources to provide more information on these novel approaches.

Overview

What are biocontrol agents?

Organisms derived from nature and used against pests, weeds, and diseases are biocontrol agents. They work by either killing, deterring, or disrupting the target.  

Understanding the different types of biocontrol can help you to choose the right one.  

Here, we explore four types of biocontrol agents and look at real-life examples of these in action. The four types of biocontrol agents we look at are: 

  • Macrobials are insects, mites, and beneficial nematodes that feed on pests. 
  • Microbials are microorganisms such as bacteria, fungi, viruses, and their derivatives. Microbial products contain microorganisms, their metabolites or their cell fragments. They can kill pests by direct infection, by outcompeting them, or by presenting a physical barrier.
  • Plants and animals emit semiochemicals, which are chemical compounds. They convey a message or signal that can modify the pest behaviour. We use semiochemicals as pest repellents, attractants, or to prevent mating.  
  • People extract natural substances directly from plants, minerals, or animals or manufacture them to mimic natural substances. They can repel and control microbes and insects. 
A package of 'Live Lady Bugs' a macrobial biocontrol agent
Figure 1: Packaged live ladybirds, a macrobial biocontrol agent © Dekayem/via Wikimedia Commons (CC BY SA 3.0)

What are macrobials?

Macrobials, also known as invertebrate biocontrol agents, are natural enemies of pests. They include predatory mites, insect predators, parasitic wasps, and entomopathogenic (insect-killing) nematodes (EPN).

Find more information on some key pests and macrobials in the Applied Bionomics Bio-control Handbook.

Examples of predatory mites

The predatory mite Amblyseius swirskii is one of the most successful commercial natural enemies in covered crops. It is a generalist predator that can feed on major greenhouse pests. Those include thrips, whiteflies, and herbivorous mites.

Examples of insect predators


IPM programs widely use the predatory mirid bug Macrolophus pygmaeus throughout Europe. It can control different insects that feed on green plants.

Examples of parasitic wasps

Parasitoids or parasitic wasps can help control populations of Lepidopteran butterflies and moths. Depending on the species, parasitic wasps can infest pests at different life stages (eggs, larvae, or adults).

A parasitoid (Trichogramma dendroliti) female on a armyworm (Noctuidae) egg
A parasitoid (Trichogramma dendroliti) female on a Noctuidae egg. © Victor Fursov via Wikipedia Commons, CC BY-SA 4.0

Examples of entomopathogenic nematodes

Entomopathogenic nematodes (EPNs) are small worm-like animals, found naturally in soils, that can kill insects. Globally, EPNs from two genera, Steinernema and Heterorhabditis, control major insect pests. They attack pests such as white grubs and the cotton bollworm.

A Heterorhabditis bacteriophora nematodes bursting from a dead wax moth larva.
Heterorhabditis bacteriophora nematodes bursting from a dead wax moth (Galleria mellonella) larva, used as biocontrols against soil-dwelling crop pests © Peggy Greb, USDA Agricultural Research Service/via Bugwood.org

For more general information, read nematodes for pest control and or watch a video of the entomopathogenic nematodes lifecycle.

What are microbials?

Microbials, or microbial biopesticides, are microorganisms such as bacteria, fungi, or viruses. Microbials also include compounds derived from microorganisms such as metabolites or fragments of cells. These biocontrol agents target various pests, such as insects, or microbes that attack plants.

Examples of fungal biocontrol agents

  • Trichoderma is a group of fungi. It works against a wide range of plant pathogens, such as Fusarium. Trichoderma is one of the most popular microbial biopesticides. Read more about Trichoderma as a biopesticide.
  • Green MuscleTM is a safe and effective biological product against locusts and grasshoppers. It contains the fungus Metarhizium acridum. It works best when used on young generations of locusts. Read about Green MuscleTM being used on locusts in Africa or watch this video on how Green MuscleTM works.
  • Purpureocillium lilacinum is a fungus that targets several species of plant parasitic nematodes. It helps control notably the root-knot nematode (Meloidogyne spp.) and the potato cyst nematode (Globodera pallida)
A cicada, on a tree infected by Beauveria bassiana, a fungal biocontrol agent
A cicada infected by Beauveria bassiana, a fungal biocontrol agent © Danny Newman (2008) via Wikimedia Commons

Examples of bacterial biocontrol agents

Most of the bacterial biopesticides are from the Bacillus genus. Bacillus species can be active against an entire order of pests (beetles, moths, etc.).

  • Bacillus thuringiensis (Bt) is the most commercially used bacterium for insect control. The strain of Bt determines which pest species are targeted.
  • For example, we can use the B. thurigiensis var. kurstakii to control larvae of Lepidopteran pests such as Tuta absoluta. Read more about Bt on the International Biological Control Manufacturers (IBMA) website. 
  • Bacillus subtilis is an effective agent against numerous plant pathogens. These include Alternaria fungi that can cause powdery mildew. Bacillus subtilis controls the fungal diseases by suppressing fungal growth.
A Bombyx mori larva Infected Bacillus thuringiesis
Bombyx mori larva Infected Bacillus thuringiesis © CABI

Examples of viral biocontrol agents

Microbials comprise a variety of viruses. The most common virus family used in biocontrol is the Baculoviruses.
They typically need ingestion to become infectious. For that reason, chewing insect pests are the main target of baculoviruses.   

  • Granuloviruses are a certain type of Baculoviruses. For example, we use them to fight the codling moth. Its caterpillars feed on fruit crops, mainly apples and pears, which can be sprayed with a specific granulovirus. 
  • Nuclear Polyhedrosis viruses or NPVs are another type of Baculoviruses. They infect several species of moths and butterflies. It can notably control the African cotton leafworm (Spodoptera littoralis) or the beet armyworm (Spodoptera exigua).
A beet armyworm larva on a leaf killed by an NPV
A beet armyworm larva killed (top) by an NPV © David Nance, USDA Agricultural Research Service/via Bugwood.org

What are semiochemicals?


Plants or animals naturally produce semiochemicals, which are chemical compounds. Organisms release them into the environment to convey a message to other organisms. They affect a pest’s behavior.

Semiochemicals, specifically pheromones, find widespread use in controlling insect pests. Researchers can also produce semiochemicals synthetically to mimic a natural compound.

Examples of semiochemicals

  • PherogenTM is a product based on sex pheromones that targets the fall armyworm (Spodoptera frugiperda). It works on the technique of mating disruption. The diffused pheromones disturb males that are searching for females. It prevents or delays the reproduction of the pest.
A PherogenTM pheromones dispenser
PherogenTM pheromones dispenser © CABI BioScience
  • Sex pheromones can be combined with traps to control a pest. This technique is used to control the male adults of the tomato leafminer (Tuta absoluta). The specific blend of pheromones attracts the males to traps. This technique is helpful in monitoring the number of individuals as well.
Pheromone trap in an orchard made from a milk carton coated in a sticky substance
Pheromone trap in an orchard made from a milk carton coated in a sticky substance © David McClenaghan/via Wikimedia Commons

What are natural substances?

Natural substances are compounds derived from nature or synthesized to closely resemble them. Plants, minerals, or animals serve as the sources from which these substances are derived. One can extract those compounds from fruits, leaves, or seeds, for example. Natural substances can have pesticide properties (kill the pest) or can repel the pest.

Examples of natural substances

  • Azadirachtin present in neem products is commonly used in biocontrol. The products are composed of extracts from fruits and seeds of the neem tree (Azadirachta indica). Its mode of action includes repelling many pests: mealybugs, aphids, nematodes, etc and preventing pests from laying eggs or feeding on plants.  
  • Thymol is an antifungal compound derived from the thyme plant (Thymus vulgaris L.). It is effective against grey rot (Botrytis cinerea) in grapevine crops. One can combine thymol with other substances, such as eugenol extracted from clove oil.

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