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Beneficial nematodes: Seeking and destroying insect pests

Theme: Biocontrol agents

Tenebrio molitor larvae
Tenebrio molitor larvae showing the distinct red colouration due to colonization by the symbiotic bacteria of the beneficial nematodes. It is in fact the symbiotic bacteria (not the nematode) that kill the insect. Copyright: CABI

Overview

What is a nematode?

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. They are macrobial products, or invertebrate biocontrol agents.

Why use nematodes?

Many insecticides face bans in agriculture because of their harmful effects on users and the environment. Nematodes can provide an effective alternative for controlling these insect pests. Pest management benefits greatly from their particular usefulness in targeting difficult-to-manage pests like white grub and cutworm larvae found in the soil.

Infective juvenile entomopathogenic  larvae emerging from an insect cadaver.
Infective juvenile entomopathogenic (beneficial/insect killing) larvae emerging from an insect cadaver. © CABI

How do I use nematodes?

In field, covered and orchard crops, turf, on solid substrates (soil, compost etc) or aerially (foliage or stems)

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.

What are the benefits of nematodes?

They 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.

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, see this video on biocontrol with nematodes

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, go to this video on Mode of Action of Koppert Nematodes

Considered safe by national authorities, for the environment, users and consumers

Studies have demonstrated that EPNs and their associated symbiotic bacteria do not cause harmful effects to humans or other vertebrates. Researchers consider any short-lived non-target effects on field populations of invertebrates.

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

Residue from chemical pesticides can be extremely damaging, especially to the environment and surrounding wildlife. As nematodes are natural, there

Reduce the need for chemical pesticides and can be used in organic farming

Using nematodes as a form of pest or disease control means there may be less need for a conventional chemical pesticide. Using natural products on crops enables farmers to sell on the organic market, yielding higher profits.

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.

Entomopathogenic larvae emerging from an insect cadaver
Entomopathogenic (beneficial/insect killing) larvae emerging from an insect cadaver. Copyright: CABI

How do I know they work?

You can see a successful example of the use of beneficial nematodes in the UK is the control of vine weevil (Otiorynchus sulcatus) in strawberries

Or, take a look at this novel Claymation presentation of the entomopathogenic nematodes.

Products based on the nematodes Steinernema spp. and Heterorhabditis spp. can be found for insect pests on www.bioprotectionportal.com.

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