8 November 1996

East faces aphid attack in wake of twin resistance

By Edward Long

POTATOES, sugar beet, and vegetable brassicas in eastern England could be wide open to aphid attack next year after the appearance of a new type of insecticide resistance.

This has combined with an existing resistance to give Myzus persicae, peach potato aphid, across-the-board protection from all widely used approved aphicides.

Arable farmers have had to cope with resistant aphids for 30 years. But until recently M persicae had the first type of resistance only. "The second type of resistance was not seen in the green aphid Myzus persicae until the early 1990s," points out research entomologist Alan Devonshire of Rothamsted Experimental Station.

Last year two individuals with the double resistance were found in Rothamsted suction traps. Earlier this autumn Rothamsted started receiving reports of aphids out of control in Lincolnshire potatoes.

Aphids with the double-barrelled resistance are largely unaffected by organophosphorous, pyrethroid or carbamate insecticides. Many arable farmers in Lincs, Cambs and other affected areas of East Anglia have resorted to using nicotine on crops as a result.

"The first reports of potato growers having trouble came in August with a hot spot in the Spalding area," Dr Devonshire says. "Since then we have widened our search and found the problem in East Anglia, and in brassicas."

The sudden flare up could be due to the widespread and concentrated use of insecticides to control silver Y moth earlier this year. That may have knocked out aphid pred-ators, and surviving green flies are more likely to have been resistant.

"I am concerned that if aphids with the new resistance survive the winter we could start the next beet season facing a serious situation," says Suffolk-based entomologist Alan Dewar of Brooms Barn Experimental Station near Bury St Edmunds. &#42


&#8226 Dual-resistance M persicae:

– enzyme neutralises chemical before it reaches aphids nervous system.

– target protein in nervous system less vulnerable.

&#8226 Resist most aphicides.

&#8226 Beet, potatoes and brassica crops at most risk.

&#8226 Dual-resistors always red.

&#8226 Gaucho remains effective.

&#8226 Silver Y moth sprays to blame?