A three-year field study on the short-term effects of insecticides used tocontrol cereal aphids on plant-dwelling aphid predators in winter wheat

Short-term effects of six insecticides used to control aphids were assessed in wheat on plant-dwelling aphid predators. Products were applied to small plots of winter wheat in June or at the beginning of July and the densitie s of predators were estimated three days after treatment using a beating me thod. Insecticides were tested in 1994, 1995 and 1997 at a single dose, cor responding to their maximum recommended field rate in Belgium. Fluvalinate and esfenvalerate did not significantly reduce catches of syrphid larvae co mpared to the control but ladybirds were affected by these compounds. Pirim icarb was the only product tested that had no effect on ladybirds. However, syrphid larvae appeared sensitive to this product. Cyfluthrin, deltamethri n and phosalone reduced catches of both syrphids and ladybirds. Populations of lacewing larvae were unaffected by any of the insecticide treatments. S yrphid larvae were the most abundant aphid predator and Episyrphus balteatu s the most common species. Ladybirds (Coccinella septempunctata and Propyle a quatuordecimpunctata) were less numerous and only a few Chrysoperla carne a larvae were recorded. These results indicate that products that are less toxic to syrphid larvae, like esfenvalerate and fluvalinate, may be prefera ble to other compounds to control cereal aphids in wheat in spring and earl y summer. However, other criteria, such as the effectiveness of the differe nt aphid-specific predators, cost, efficacy of the treatment and side effec ts on other aphid antagonists (including parasitic hymenoptera and polyphag ous predators) must also be taken into consideration. (C) 2000 Society of C hemical Industry.