Monitoring data from 2007 suggest the UK is facing a growing problem with pyrethroid-resistant pollen beetles.

In 2006 pyrethroid-sensitive pollen beetles completely dominated the sampled population, Ralf Nauen of Bayer CropScience said at the BCPC’s International Plant Protection Congress. “But in 2007 there were locations where the 100% field rate would only have given between 30 and 60% control.”

Overall most of the UK population remained susceptible to pyrethroids, he said. “But it shows perhaps there is a problem coming up in the UK.”

Most of the UK resistant populations were on the coastal fringes, his colleague Bill Lankford told Farmers Weekly. “We found resistance in Kent, Essex, Suffolk and Norfolk. Most research suggests the beetles can spread by around 50 miles a year, so in four or five year’s time 90% of our crop could be affected.”

It meant it was important to learn from the German experience, where resistant beetles had cost the industry €25m in 2006. “It was disastrous,” Dr Nauen said.

The key to better control was having different modes of action available, he said. Up until 2006 the German’s had relied solely on pyrethroids, but alternative chemistry in thiacloprid (as in Biscaya) and chlorpyrifos-methyl had been approved, in the latter case for a restricted 500,000ha area. Both control pyrethroid-resistant pollen beetles.

Biscaya was approved for use in the UK, Dr Lankford said, but not much had been used commercially so far. But he suggested it should become first choice for growers in areas where resistant pollen beetles had been found. “It makes sense to use it in these areas. If you use pyrethroids, any resistant pollen beetles’ offspring will also be resistant, and you could exacerbate the problem.”

•  Turn to p45 for a possible way of overcoming resistance in insects.