Types of biocontrol agents​

Types of biocontrol agents

  • 3.1 What are biocontrol agents?

    Biocontrol agents are organisms, or material derived from nature, which are used to manage pest problems. These are often grouped into four main types, natural enemies (or invertebrate biocontrol agents), microbials (living organisms, metabolites or fragments of cell walls), semiochemicals (chemicals emitted by plants, animals or other organisms for intra- and/or inter-species communication, are target specific and non-toxic) and natural substances (materials which originate in nature or are identical if synthesised).

  • 3.1.1 Macrobials
    What are macrobials?

    Macrobials, or Invertebrate biocontrol agents, are natural enemies including mites, insect predators, parasitioids and nematodes which control pests. Some examples are provided below:

    Natural enemies

    Useful background information on some key pests and their management with macrobial biocontrol agents can be found in the Applied Bionomics  Bio-control Handbook .

     

    Amblyseius swirskii: The predatory mite A. swirskii is one of the most successful commercial natural enemies in covered crops. It is a generalist predator and is used commercially to control the major greenhouse pests; thrips, whiteflies and mites. More information regarding this natural enemy can be found in the BioProtection Portal Blog, “Top predator for protecting your covered crops: Amblyseius swirskii”.

    https://bioprotectionportal.com/blog/2021/top-predator-for-protecting-your-covered-crops-amblyseius-swirskii-2

    A predatory mite Amblyseius swirskii attacking a food mite Carpophagus sp.

    An example of a successful application of the A. swirskii can be illustrated with a case study from Spain, where it has been used to control pests in honey melon, https://www.ibmabiocontrolsuccess.org/ case /swirskii-predatory-mite- controls-pests-in-greenhouse-in-honey-melon-in-spain/ and also in aubergine production in Spain.

    https://www.ibmabiocontrolsuccess.org/ case/predatory-mites-and-insects-control-pests-in-greenhouse-eggplant-in-spain/

     

    Watch the video below to see how the predator A. swirskii actively manages the whitefly pest in the glasshouse.

     
    Entomopathogenic nematodes

    Nematodes, or more specifically insect killing (entomopathogenic) nematodes (EPNs), can be found naturally in the environment as parasites of insect larvae. Nematodes from two genera, Steinernema and Heterorhabditis, are used globally to control major insect pests within a range of different crop production systems. With the withdrawal of many insecticides due to their harmful effects on users and the environment, nematodes can offer an effective alternative to controlling these insect pests. They are particularly useful in managing pests that are difficult to target such as white grub and cutworm larvae which are found in the soil.

    Nematodes are a useful tool for management of insect pests as they;

    • Can be used in field, covered and orchard crops, as well as turf

    There are many commercial examples of the use of EPNs: in field crops to control soil-dwelling insect larvae of Cutworms (Agrotis spp.), in glasshouse crops to control larvae of fungus gnats (Bradysia spp.), in fruit orchards to control Codling moth (Cydia pomonella) and white grubs (including Japanese Beetle, Popillia japonica) of turf grass.

    • Can be applied to solid substrates (soil, compost etc) or aerially (foliage or stems)
    • Can actively search for the target pest, depending on the species

    For example, Steinernema carpocapsae utilizes an “ambush” strategy, waiting near the soil surface for target hosts, whilst Heterorhabditis bacteriophora has a “cruiser” strategy, seeking out its target.

    • Have specific and narrow host ranges

    The EPNs are parasites of insects and the range of targets can vary with S. feltiae, for example, attacking Coleoptera, Diptera, Lepidoptera and Hymenoptera whilst in contrast H. bacteriophthora only attacks Coleoptera, mainly Scarabidae. To see how the nematodes interact in a living system

    • Are unlikely to promote resistance within host insects

    The EPNs themselves will not kill a host insect; this requires the EPNs symbiotic bacteria. When an EPN enters a host insect larva they release their symbiotic bacteria which kill the insect host. The bacterial enzymes then digest the larva and the EPNs feed on the products. To see an animated explanation of the mode of action

    • Are considered safe by national authorities, for the environment, users and consumers

    The EPNs and their associated symbiotic bacteria have been shown to have no harmful effects to humans or other vertebrates. Any non-target effects on field populations of invertebrates are considered to be short-lived.

    • Will not feed on plant material

    The EPNs are not related to plant parasitic nematodes and do not utilize plant material as a food source.

    • Do not produce any residue in crops
    • Reduce the need for chemical pesticides
    • Can be applied using existing spray or irrigation systems

    When using conventional spray equipment or overhead irrigation, make sure to remove filters and sieves, and ensure the nozzles are of at least 0.5mm diameter, and use low pressure to prevent damaging the EPNs.

    • Can be used with other biological agents or integrated pest management (IPM) components

    EPNs can be applied together with other biologicals such as Bacillus thuringiensis (Bt) or conventional insecticides such as Imidacloprid to manage insect pests, often with synergistic effects or the effective use of lower doses of insecticides.

    • Can be used in organic farming

    A successful example of the use of beneficial nematodes in the UK is the control of vine weevil (Otiorynchus sulcatus) in strawberries https://www.ibmabiocontrolsuccess.org/ case/beneficial-nematodes-epn-control-vine-weevil-in-strawberry-in-uk/

    For a novel Claymation presentation of the entomopathogenic nematodes watch the video below.

     
  • 3.1.2 Microbials
    What are microbials?

    Microbials are micro-organisms, including bacteria, fungi and viruses and may also include their metabolites or fragments of cells.

    Examples of fungal biocontrol agents
    Trichoderma: A biopesticide with multiple modes of action and more besides
    Radial growth of Trichoderma stromaticum with characteristic sporulation on an agar plate

    Trichoderma is a fungal group which contains a wealth of species used as commercial biopesticides. It is one of the most commonly used microbial biopesticides, with nearly 200 commercial products in the Americas, Europe, Asia and Africa. However, its use is much greater than the commercial sector with many local informal production facilities producing Trichoderma at a farm or community level.

    Why is Trichoderma so successful?
    A direct approach

    Trichoderma spp. are primarily recognized for their direct biocontrol action against a wide range of pathogens, both soilborne and those on the aerial parts of crop plants. These pathogens include fungal and oomycete pathogens, such as Rhizoctonia, Fusarium, Verticillium, Pythium and Phytophthora. Although Trichoderma usually attack a wide range of pathogens, there are also those which have evolved to target a particular pathogen, such as T. stromaticum, which is effective against the witches’ broom pathogen in Brazilian cocoa orchards. These direct actions include;

    Mycoparasitism; where the fungus colonizes and feeds on the mycelium of the host fungus

    Antibiosis; where its metabolites directly act against the target pathogen

    Competitive exclusion; where the physical presence of the Trichoderma actively prevents access to a host plant.

    An indirect approach

    In addition to these direct methods of antagonism towards a pathogen or group of pathogens, Trichoderma has other more subtle means by which it can aid a crop in combating pathogen attack. Close association of the Trichoderma within the rhizosphere, around the roots or within the roots, or even as an endophyte within other aerial tissues of the plant, can have a profound effect on the host plant. This includes;

    • Increasing the solubilization and uptake of nutrients, thus improving the general health and fitness of the crop
    • Activating the host plant’s defence system, priming it for a more effective response to the presence of a pathogen; analogous to human vaccination and subsequent immune response! This maybe local – or systemic – (throughout the host plant) induced resistance.
    • Providing tolerance to abiotic stress such as drought, which in turn will provide resilience to a pathogen attack.

    The extent to which these more subtle effects are expressed may be highly dependent on the Trichoderma spp. or strain selection for a given cropTrichoderma spp. colonising, and sporulating on, mycelium of Moniliophthora roreri (frosty pod rot pathogen) on a cacao pod

    Where can Trichoderma be used?

    Trichoderma can be used for crop protection in a wide range of production systems. It can be effectively used, dependant on manufacturers’ recommendations and national registration for;

    • Covered crops, greenhouse or polytunnels
    • Field crops
    • Orchard crops

    It can also be used in forestry, in nurseries for seedling production, but can also be used to manage the more rapid destruction of inoculum such as Armillaria spp. (in tree crops) and also Ganoderma spp. (in Oil Palm) by application to diseased material in the field.

    Want to find out more about Trichoderma and its role in crop protection?

    See how Trichoderma has been successfully applied in Spain for lettuce production in the field

    Metarhizium 

     

    Examples of bacterial bioprotection agents

    Coming soon

     

    Examples of virus bioprotection agents

    Coming soon

     
    3.1.3 Semiochemicals
    What are semiochemicals?

    Semiochemicals are chemicals emitted by organisms which act inter- or intra-specifically as a means of communication. They can act as attractants or repellants and have a specific, non-toxic mode of action.

    Examples of semiochemicals

    Coming soon

    3.1.4 Natural Substances
    What are natural substances?
    Natural substances arethose materials derived from nature, or when synthesised are indistinguishable from the natural material.
    Examples of natural substances
    Coming soon