Field experiments on the effects of a new pyrethroid insecticide WL‐85871 on bees foraging artificial aphid honeydew on winter wheat

Abstract

AbstractTwo large and two small plots of winter wheat were enclosed beneath large mesh‐covered tunnels. A small beehive was placed in each tunnel and sucrose solution was sprayed on to all of the wheat in order to simulate aphid honeydew. WL‐85871 (a 1:1 mixture of two stereoisomers of cypermethrin) as ‘Fastac’ at three dose rates, dimethoate, pirimicarb or water were applied to the larger plots of wheat when the bees were actively foraging the sugar deposits. No increase in bee mortality, compared with that in the pre‐treatment period, was observed after the applications of WL‐85871 or pirimicarb. By contrast, large numbers of dead bees were found following the applications of dimethoate. Foraging activity in the plots, treated with all dose rates of WL‐85871 or with pirimicarb, declined sharply after treatment and remained at a reduced level. With dimethoate no foraging activity occurred after application in either the treated or untreated plots. Only very low concentrations of WL‐85871 were detected in post‐treament samples of honey, wax, and live or dead bees. It was concluded that the application of WL‐85871, to wheat already treated with artificial honeydew, resulted in no adverse effects on the honey‐bee colonies.