Latest evidence in hunt for beetles’ resistance

A field of oilseed rape near Halvergate.Picture: James Bass

A field of oilseed rape near Halvergate.Picture: James Bass - Credit: Eastern Daily Press © 2013

Latest research has suggested, as many oilseed rape growers feared, that resistance to pyrethroids in UK populations of cabbage stem flea beetle is widespread.

Following a pre-harvest call for suspected pyrethroid resistant beetle samples to be sent to Rothamsted Research for analysis, knock-down resistance (kdr) to pyrethroids has now been confirmed in every UK sample tested so far.

The HGCA is now calling for more growers and agronomists to send suspected resistant samples to Rothamsted Research to build an even more robust picture of resistance in the UK.

Caroline Nicholls, HGCA research and knowledge transfer manager, said: 'The researchers at Rothamsted developed a genetic test to look for the mutation associated with kdr resistance previously reported in Germany. The results found resistant beetles in all samples tested so far.

'This is a cause for concern as this type of resistance is likely to cause control problems with all pyrethroids applied at recommended field rates.'

The frequency of resistant individuals has also been surprisingly high, according to the analysis.

This may in part be down to a potential bias caused by the fact samples were typically taken where resistance was suspected.

Most Read

Further to the genetic test, live beetles were also placed in glass vials coated with lambda-cyhalothrin, the pyrethroid which is found in a number of insecticides authorised for use in oilseed rape.

A range of doses, including the equivalent of recommended field rate, were tested. Once again, resistance was detected in all samples.

Researchers now need more adult beetle samples to continue their work.

'We have been contacted by a number of growers concerned about cabbage stem flea beetle in emerging oilseed rape crops wanting to send in samples for analysis,' said Miss Nicholls.

'Unfortunately, there isn't a tried-and-tested approach for collecting live samples in the field at this time of year.

'We found the best way to catch live beetles is to go out at night with a torch to find beetles. Once located, beetles can then be trapped using a jar.'

HGCA's revised cabbage stem flea beetle publication provides further information on assessing the need to spray larvae as well as adult beetles.