Stage-Dependent Bendiocarb Tolerance in the German Cockroach (Dictyoptera: Blattellidae)

Topical insecticide bioassays revealed that last-instar German cockroach, Blattella germanica (L.), nymphs were up to 19.8-fold more tolerant of bendiocarb than adult males. Pretreatment with the cytochrome P450 monooxygenase inhibitor, piperonyl butoxide, eliminated this difference. Acetylcholinesterase activity was equally inhibited by bendiocarb in both the last-instar nymphal and adult male stages. The bimolecular rate constant (ki) for adult males was 3.58 × 105 ± 1.0 M−1min−1, which was not statistically different from nymphs at 3.33 × 105 ± 1.1 M−1min−1. Similar ki values indicate that altered acetylcholinesterase does not contribute to the increased nymphal tolerance to bendiocarb. These results indicate that increased detoxification catalyzed by microsomal oxidases is responsible for the enhanced nymphal tolerance to bendiocarb in the Village Green strain.