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The insecticide chlordimeform and its A'-demethyl metabolite, iV,-(4-chloro-o-tolyi)-Ar-methylformamidine or demethylchlordimeform, were more .toxic to third instar cabbage looper larvae than to fifth 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 third instar larvae than in fifth instar larvae. There were no apparent qualitative differences in the chlordimeform metabolites between the two larval instars but quantitative differences were evident. Third instar larvae converted chlordimeform to demethylchlordimeform and to polar metabolites slower than did fifth instar larvae. Metabolism studies with demethylchlordimeform-14C revealed a similar trend between the two instars. The slower penetration and metabolism of chlordimeform in third instar cabbage looper larvae as compared to fifth instar larvae may explain, at least in part, the differential toxicity.Chlordimeform has an interesting spectrum of insecticidal activity, being toxic primarily to eggs and early

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