Seek and destroy: use of nematodes for insect pest control​

A közönséges lisztbogár (Tenebrio molitor) lárvája, melynek határozott vöröses csíkjai vannak világos alapon
Tenebrio molitor larvae showing the distinct red colouration due to colonisation by the symbiotic bacteria of the beneficial nematodes. It is in fact the symbiotic bacteria (not the nematode) that kill the insect. © CABI

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 many insecticides being banned from use in agriculture 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.

Infective juvenile insect killing larvae emerging from a dead insect.
Infective juvenile entomopathogenic (beneficial/insect killing) larvae emerging from an insect cadaver. © CABI
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, see https://www.youtube.com/watch?v=jM4kZsQntxU

·       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, go to https://www.youtube.com/watch?v=kohR7sdCbAE&feature=emb_rel_end

·       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

Beneficial larvae emerging from an insect cadaver.
Entomopathogenic (beneficial/insect killing) larvae emerging from an insect cadaver. © CABI

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, see https://www.youtube.com/watch?v=wZ1LDXkyp6Y

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