A comparison of the effect of new and established insecticides on nontarget invertebrates of winter wheat fields

Six insecticides, a carbamate (pirimicarb), four pyrethroid/mixtures (tao-fluvalinate, zeta-cypermethrin, deltamethrin, and pirimcarb+deltamethrin), and an organophosphate (dimethoate), registered for use within cereals, were field-tested for toxicity to beneficial nontarget invertebrate groups important as food for farmland birds. Compared to the control and the other compounds, pirimicarb was the least toxic for most invertebrate groups examined. The pyrethroids and pyrethroid mixture significantly reduced numbers of many of the nontarget groups compared to the control and pirimicarb. Tao-fluvalinate was the least toxic pyrethroid tested when compared to the other compounds. Toxicity was further tested on larvae of graminivorous sawflies, an important chick-food group, using field-sprayed plants in laboratory and semifield trials. None of the pyrethroid and carbamate compounds and mixtures was as toxic as the organophosphate, but all were more toxic than the control. The semifield experiments provided a useful way of determining potential insecticide impact on this nontarget group where field populations are often too low for field trials to have statistically conclusive results.