A better understanding of the range of biocontrol agents and the way in which they interact with the target pest can help in the selection of a suitable agent for your production system, but also provide insight into how they can be more effectively used. Here we provide additional information and resources to provide more information on these novel approaches.

What are biocontrol agents?

Biocontrol agents are organisms derived from nature used against pests, weeds and diseases. 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. They include compounds, microorganisms, and their cell fragments. They can kill pests by direct infection, by outcompeting them, or by presenting a physical barrier.
  • Semiochemicals are chemical compounds emitted by plants and animals. They convey a message or signal that can modify the pest behaviour. We use semiochemicals as pest repellents, attractants, or to prevent mating.  
  • Natural substances are extracted directly from plants, minerals, or animals or are manufactured to mimic a natural substance. They can repel and control microbes and insects. 

Figure 1: Packaged live ladybirds, a macrobial biocontrol agent copyright 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

The predatory mirid bug Macrolophus pygmaeus is widely used in IPM programmes 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).

Trissolcus japonicus parasitizing eggs of the Brown Marmorated Stink Bug, Halyomorpha halys © Tim Haye, CABI

Examples of entomopathogenic nematodes

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

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 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

  • ট্রাইকোডার্মাঃ is a group of fungi. It works against a wide range of plant pathogens, such as Fusarium. ট্রাইকোডার্মাঃ 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 it is 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 infected by Beauveria bassiana, a fungal biocontrol agent © Danny Newman (2008) via Wikimedia Commons

Examples of bacterial bioprotection 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.

Bombyx mori larva Infected Bacillus thuringiesis © CABI

Examples of viral bioprotection agents

Microbials comprise a variety of viruses. The most common virus family used in biocontrol is the Baculoviruses. They usually need to be ingested 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 killed (top) by an NPV © David Nance, USDA Agricultural Research Service/via Bugwood.org

What are semiochemicals?

Semiochemicals are chemical compounds naturally produced by organisms like plants or animals. They are released into the environment to convey a message to other organisms. They affect a pest’s behavior.

Pheromones are a type of semiochemicals that are widely used to control insect pests. Semiochemicals can also be produced 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.

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 © David McClenaghan/via Wikimedia Commons

What are natural substances?

Natural substances are compounds derived from nature or synthesized to closely resemble them. They are derived from plants, minerals, or animals. Those compounds can be extracted 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. Thymol can be combined with other substances like eugenol extracted from clove oil.

Other Resources

Learn biocontrol online

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