Laboratory efficacy screening of insecticides for control of Maladera matrida larvae

Maladera matrida Argaman (Coleoptera: Scarabaeidae) was first reported in the central coastal plain of Israel in the early 1980s and was subsequently described as a new species. By the late 1980s it had spread southward to the northwestern Negev desert region, where heavy infestations of this pest caused significant economic losses, especially to growers of peanuts and sweet potatoes. Larvae (white grubs) ofM. matrida feed on underground parts of plants. We used a laboratory soil-treatment assay for determining the relative toxicity of several insecticides to 3-week-old grubs. Insecticides, both registered and candidates for registration, were tested at the labeled rates for field crops. The residual activity of those insecticides that caused ≥60% mortality of grubs after the first week, was studied for two additional weeks, by replacing the grubs with new ones each week. The granular formulation of the organophosphate insecticides terbufos, chloropyrifos, ethoprop and isazofos induced a uniform high mortality to grubs throughout the study period. Chloropyrifos and ethoprop caused >90% mortality also at one tenth of the labeled rate. Also diazinon brought about >90% mortality after the first week, but subsequently lost its activity. Imidacloprid, bendiocarb, fenitrothion, acephate, methamidophos and carbaryl provided <50% mortality during the first week.