Resistance to pyrethroids in grain aphids (Sitobion avenae) appears likely to have been the cause of failures in controlling aphids last summer, while neonicotinoid resistance in Myzus persicae is heading north from southern Europe.

Rothamsted Research DNA tests had found the kdr mutation in grain aphids, which is known to confer resistance in Myzus persicae to pyrethroids, Steve Foster, research entomologist at Rothamsted, told agronomists at the HGCA Agronomists conference.

“We have aphids with kdr in them from a range of geographical locations, including those associated with control failures. What we need to do now is take live aphids and do bioassays to test how big the resistance factors are, and test cross resistance across the pyrethroids.”

That work was ongoing, and should be completed in around a month, he said. “If the resistance conferred is high, it could cause real problems in controlling these aphids.”

No similar resistance had been found in other cereal aphids, however, he stressed and so far, control problems had only been found when trying to control summer aphids.

Better news was that no resistance to neonicotinoid insecticides or other new insecticides, pymetrozine (Plenum) and flonicamid (Teppeki), had been found in Myzus persicae in the UK, he said. “The UK does not appear to be selecting for resistance with what we are doing.”

But resistance had been found in southern Europe in Myzus persicae. “We now have control-busting resistance and it appears to be moving north, just as MACE resistance did.”

So far, resistance had only been in aphids found on peach trees. “But there is no reason why it should just be restricted to peach.” Indeed, laboratory tests carried out by Dr Foster had shown the aphids capable of transferring onto crops, such as potatoes and oilseed rape, without any problems.

“It means they would cause a lot of problems if they got into these crops in the UK.”

Other tests suggested the highly-resistant aphids were good at avoiding predation from parasitoid wasps, which only left cold weather as a potential unknown Achilles heel, he said.

However, using neonicotinoid insecticidal seed treatments rather than foliar sprays could help minimise the impact of any resistance, he suggested. Resistant aphids treated directly with a neonicotinoid insecticide had much higher resistance factors than those who took up the chemical from within a plant, he explained.

“So this tells us how you apply the insecticide in the field has a big influence on selection pressure and resistance risk.”

For more on the HGCA Agronomist Conference see our dedicated page.