Rothamsted Research is asking oilseed rape growers to send samples of adult cabbage stem flea beetles collected at harvest to assess levels of both pesticide resistance and parasitisation by natural enemies in the UK.
The call is part of a project to determine if a wasp recently discovered to parasitise the beetles might be an effective biocontrol agent.
Cabbage stem flea beetle numbers have been increasing since the 2013 ban on neonicotinoid seed treatments in oilseed rape was introduced, with serious yield losses reported, especially in the east and south-east of the country.
Pyrethroid sprays are currently the only control option, but resistance to them is widespread.
Patricia Ortega-Ramos, who is conducting the research, said without accurate information on the susceptibility of local populations, each treatment is a gamble.
“Farmers are risking economic loss, increased pest resistance and harmful impacts on non-target organisms. But there is new hope for control.
“Recently, a natural parasitoid of the adult stage of flea beetles has been found and studies on its lifecycle have revealed that the larvae of this wasp develop inside the adult beetle and kill them when they emerge.”
The new project aims to understand the mechanics of resistance and the potential for biological controls.
To ensure a good sample size, Rothamsted is asking farmers to send at least 250 beetles to assess both pyrethroid resistance and parasitisation rate.
In return, the institute will provide farmers with data for their own area and a measure of how it compares nationally.
Sampling kits, consisting of an electric “pooter”, which hoovers the insects up, along with plastic containers to return them in, will be provided to the first 40 farmers who sign up.
Ms Ortega-Ramos said the best way to collect beetles is from the grain at harvest, either from trailers or stores.
Farms in areas where flea beetle populations are known to be low, making it unlikely to sample more than 250 beetles, can still send at least 50 beetles for pyrethroid resistance testing only.