Nematodes which infest and kill one of the world’s most notorious moth pests work most effectively when applied in a gel formulation.
In a study by research partners in Switzerland and Rwanda, the nematodes Steinernema carpocapsae and Heterorhabditis ruandica in a cellulose-based gel killed 100% of caterpillars of the fall armyworm (Spodoptera frugiperda) on maize plants under lab conditions, compared to 74% and 94% when applied with either water or a surfactant, respectively.
Although S. frugiperda can damage hundreds of different crops, it causes huge impact in maize, meaning it is considered a major threat to food security.
With pesticides mainly used to combat the pest, the researchers looked to test out their more ecologically-sustainable option in the field. Although all the formulations tested in the lab reduced damage to crops, only the gel formulation reduced caterpillar infestation levels – performing with the same effectiveness as a standard dose of the insecticide cypermethrin.
“These findings demonstrate that entomopathogenic nematodes, when properly formulated, are excellent candidates for the biological control of fall armyworm, and can be a safe and sustainable alternative to synthetic insecticides,” wrote the researchers.
Top option for crop and context
Applications of nematodes are particularly suited to maize, as S. frugiperda caterpillars are generally hidden when feeding. This undermines the effectiveness of conventional insecticide sprays, whereas nematodes are able to actively forage for their prey.
Despite the success of the formulation, multiple applications may be required over the course of a growing season to account for moths re-infesting the crop.
“Controlling fall armyworm through the use of formulated entomopathogenic nematodes seems particularly realistic in an African and Asian context, where low tech manual labour is predominantly used in pest management efforts, allowing manual spot applications in maize fields,” they continued.
With a relatively low number of nematodes required in the formulation, as well as the local availability of insect-killing nematodes in affected countries, there is the prospect of smallholders producing their own nematode products, they added. Alternatively, large-scale commercial applications would also be possible.
You can read the full research report in Biological Control.
