Effects of Insecticides on the Entomopathogenic Nematode Steinernema carpocapsae WEISER

The toxic effects of 14 organophosphates (OP's), 7 carbamates, 4 synthetic pyrethroids, cartap and imidacloprid on the entomopathogenic nematode Steinernema carpocapsae WEISER were tested by checking the mortality of infective juveniles (IJs) in insecticide solutions. Cartap and two OP's (profenofos and pyraclofos) were the most toxic to the IJs: 83.4% mortality for cartap and 57.1 and 47.8% for profenofos and pyraclofos, respectively, in solutions of 100μg/ml after 48 h exposure. Seven OP's (diazinon, dichlorvos, fenthion, malathion, trichlorfon, propetamphos and prothiofos) showed weak toxicity at 100μg/ml. Other chemicals tested showed no toxicity to the IJs at 100μg/ml. The IJs were incubated in insecticide solutions (100μg/ml) for 24 h and then used to treat newly-molted last instar Spodoptera litura larvae. OP's (except acephate, malathion and temephos), 1 carbamate (methomyl), 2 pyrethroids (permethrin and ethofenprox) and cartap apparently inhibited infectivities of IJs to these larvae. However, when insecticides were washed off the body surface of IJs, only cartap (⪈ 10μg/ml) and profenofos (100μg/ml) left a detrimental effect on the IJ infectivity.