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 parasitization by natural enemies in the UK.

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In return, the Institute will provide farmers with data for their own area and a measure of how it compares nationally.

The call for insects is part of a project to determine if a wasp recently discovered to parasitize the beetles might be an effective bio-control agent.

Cabbage stem flea beetle numbers have been increasing since the 2013 ban on neonicotinoid seed treatments in oil seed rape (OSR) with serious yield losses, especially in the East and South-East of the country.

Pyrethroid sprays are currently the only control option, but resistance to them is widespread in the UK.

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 have been found and studies on its life cycle have revealed that the larvae of this wasp develop inside the adult beetle and kill them when they emerge. However, the biocontrol potential and distribution of these parasitoids are still unknown.

“Through this study we aim to understand the mechanisms of pyrethroid resistance developing in UK populations, and the importance of parasitoids in biological control.”

To ensure a good sample size they are asking farmers to send them at least 250 beetles to assess both pyrethroid resistance and parasitization rate.

As an extra incentive, 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 to collect 250 beetles.

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 CSFB populations are known to be low, making it unlikely that you can sample more than 250 beetles, can still send at least 50 beetles for pyrethroid resistance testing only.

The results from samples will be sent back, detailing the degree of susceptibility /resistance to pyrethroids of the beetles and the percentage parasitization of that population. Rothamsted will also provide data so that farmers can compare their situation with the ‘national average’.

Farmers wishing to get involved can contact: 

patricia.ortega-ramos@rothamsted.ac.uk or caitlin.willis@rothamsted.ac.uk