The insecticidal and neuroblocking potencies of three imidacloprid metabolites were measured using American cockroaches. The minimum doses to cause paralysis 24 hr after injection of 4,5-dehydroimidacloprid (
2) and 5-hydroxyimidacloprid (
3) were about ten times larger than that for imidacloprid (
1). Pretreatment with synergists, piperonyl butoxide and NIA16388, enhanced the activity: doses were 1.9, 1.7, and 0.071 nmol for compounds
2,
3 and
1, respectively. The concentrations of compounds
2 and
3 causing a neuroblock in the excised central nerve cord of the insects were respectively 49 and 150 μM, compared to 2.3 μM for
1. The potency of 4,5-dihydroxyimidacloprid (
4) was far inferior in both measurements. Insecticidal effects of imidacloprid and possible metabolites were discussed. © Pesticide Science Society of Japan
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