Written by Lucy Crowther. Nematodes are a hugely diverse group of microscopic, unsegmented threadworms that are found all over the globe. Although harmless to humans, these nematodes are used for organic biological pest control in our vegetable patches. While some nematodes are serious pests in their own right, such as the potato cyst nematode, other species can be used to our advantage to control crop pests.
Here, we will think about entomopathogenic nematodes (Steinernema and Heteorhabditis) and nematodes parasitic to slugs (Phasmarhabditis), how these nematodes kill and how we can expand their use outside our garden fences and into large scale agricultural systems as part of an integrated pest management system.
How do they kill?
Depending on the species of nematode there are two different ways that they go about finding their host; CRUISERS, those that actively move about their environment to find hosts and AMBUSHERS, those that sit and wait for hosts to pass them.
Once a host has been found, the infective juvenile nematode will enter the hosts body cavity through any opening or the cuticle, where they will release their symbiotic Xenorhabdus bacteria. The bacteria will then produce toxins that kill the insect host, liquifying its insides. The nematode will feed on the host, develop into adults, and go on to reproduce.
How are they beneficial?
- Entomopathogenic nematodes can be used on a wide variety of crop pests but remain targeted enough that beneficial insects will not be negatively affected.
- Nematodes are fast acting and can kill the targeted crop pest within 48 hours.
- Nematodes can be easily cultured in artificial environments so are good candidates for commercial production.
- When stored in the correct conditions, the nematodes can remain alive and stable in their infective juvenile stage for a relatively long period of time. Additionally, in this stage they can live for some time without sustenance.
- Evidence suggests that nematodes can tolerate being mixed with some agrochemicals.
- There appears to be no evidence of resistance to the symbiotic bacteria associated with entomopathogenic nematodes.
Making the move to the field
The first instances of nematodes being used successfully in commercial agricultural setting was over 40 years ago. Considerable progress has been made since then to better understand ecology, taxonomy, host range and application techniques to increase efficiency in the field.
Nematodes can be successfully applied as a soil application and a foliar spray, but immediate survival in the field can be limited by UV exposure, desiccation and success in finding a host. Application techniques can be altered to reduce these effects, evening applications and addition of humectant adjuvants.
To make the move to a totally nematode based pest management may not be the most practical or effective solution. Instead, assessments of synergisms between entomopathogenic nematodes and other methods of conservation or chemical control may be the best way forward to incorporate the more environmentally and ecologically friendly techniques into commercial systems.