Mechanisms Responsible for Cypermethrin Resistance in a Strain of German Cockroach, Blattella germanica

Cypermethrin resistance level and mechanisms responsible for the resistance were investigated in a strain (Aves) of German cockroach, Blattella germanica (L.), collected recently from a Gainesville, Florida residence. Topical bioassay data revealed that the Aves strain was highly resistant to cypermethrin, exhibiting a resistance ratio of 93-fold, which was reduced to 29fold when cockroaches were pretreated with piperonyl butoxide and reduced to 18-fold when pretreated with S,S,S-tributyl phosphorotrithioate. The synergist data implicated enhanced oxidative and hydrolytic metabolism as resistance mechanisms in the Aves German cockroach strain. This conclusion was further supported by significantly higher oxidative (2.4to 4.2-fold) and hydrolytic (1.6- to 3.6-fold) detoxification enzyme activities toward surrogate substrates and significantly higher in vitro [14C]cypermethrin metabolism. Microsomal NADPH-dependent (1.8-fold) and NADPH-independent (2.2-fold) [14C]cypermethrin metabolism were significantly greater in the Aves strain than in the Orlando insecticidesusceptible strain. In vivo penetration studies with [14C]cypermethrin indicated that decreased cypermethrin penetration may also be a contributing resistance mechanism in the Aves strain. Finally, the Leu993Phe mutation, shown previously to be associated with knockdown resistance (kdr), was present in the Aves strain.