TOXICITY, PENETRATION, AND METABOLISM OF CHLORDIMEFORM AND ITS N-DEMETHYL METABOLITE IN CABBAGE-LOOPER LARVAE

The insecticide chlordimeform and its N-demethyl metabolite, N''-(4-chloro-o-tolyl)-N-methylformamidine or demethylchlordimeform, were more toxic to 3rd instar cabbage looper [Trichoplusia ni] larvae than to 5th instar larvae, with the parent formamidine being the more toxic in each case. When both larval instars were treated topically with the same amount of chlordimeform-14C, penetration was slower in 3rd instar larvae than in 5th instar larvae. There were no apparent qualitative differences in the chlordimeform metabolites between the 2 larval instars but quantitative differences were evident. Third instar larvae converted chlordimeform to demethylchlordimeform and to polar metabolites slower than did 5th instar larvae. Metabolism studies with demethylchlordimeform-14C revealed a similar trend between the 2 instars. The slower penetration and metabolism of chlordimeform in 3rd instar cabbage looper larvae as compared to 5th instar larvae may explain, at least in part, the differential toxicity.