Toxicity and Synergism of Some Insecticides against Larvae of Thrips palmi KARNY (Thysanoptera: Thripidae).

Abstract

The susceptibilities of Thrips palmi collected from Kishigawa and Inami, Wakayama Prefecture, Honshu, Japan, to some insecticides were determined by a spray method during 1985-91. Females collected from cucumber or kidney bean [ Phaseolus vulgaris] fields were released on leaf discs of kidney bean and kept at 25°C for 2 days for oviposition. Insecticides were sprayed on the 2- to 3-day-old larvae. The LC50s for fenobcurb [fenobucarb], methidathion and cypermethrin were 428-821, 137-551 and 16-41 p.p.m. for the Kishigawa population, and 558-1266, 440-911 and 29-76 p.p.m. for the Inami population, resp. No remarkable changes with time were observed in the susceptibilities to these pesticides. However, the susceptibility of the Kishigawa population to sulprofos decreased from 1990, reaching an LC50 of 572 p.p.m. in 1991. Field experiments also showed that sulprofos failed to control T. palmi in that region. The toxicities of binary mixtures of some insecticides to larvae of T. palmi were examined. Strong synergism was found with sulprofos/cypermethrin, sulprofos/fenobucarb and methidathion/fenobucarb mixtures.