COMPARISON OF IMIDACLOPRID WITH CARBAMATE INSECTICIDES, AND THE ROLE OF PLANTING DEPTH IN THE CONTROL OF FALSE WIREWORMS, SOMATICUS SPECIES, IN MAIZE

A nitromethylene insecticide (imidacloprid) was compared in laboratory experiments with three carbamate insecticides (carbofuran, carbosulfan and furathiocarb) for the control of false wireworms, Somaticus spp., in maize. In further greenhouse experiments, the effect of planting depth on the action of the above-mentioned insecticides and another two carbamates, benfuracarb and thiodicarb, was determined. The active ingredient of all insecticides was systemically translocated to the leaves. Imidacloprid had an antifeedant action in the subterranean stems, inhibiting larval feeding deeper than the outer leaf sheath. This restricted feeding resulted in lower larval mass gain than in carbamate treatments. Severe damage to maize stems in carbamate treatments indicated the absence of antifeedant action. The number of damaged plants increased with increasing planting depth, irrespective of the insecticide used. However, although the extent of damage was similar at all planting depths for a particular insecticide, the damage index value of imidacloprid-treated plants was significantly lower than that of carbamate-treated plants.