Toxicological and biochemical characterization of insecticide resistance in a field-collected strain of Blattella germanica (Dictyoptera: Blattellidae)

A combination of insecticidal, biochemical, and electrophoretic assays were conducted on adult male and Ist instars of a field-collected strain of German cockroach, Blattella germanica (L.) (Muncie'86), to characterize its insecticide resistance. In topical applications to adult males, 11 technical grade insecticides were tested over 3 yr. These included representatives of 4 chemical classes: (1) pyrethroids (5 compounds), (2) organophosphates (3 compounds), (3) carbamates (2 compounds), and (4) cyclodienes (1 compound). The highest levels of resistance were to chlordane and bendiocarb with a resistance ratio at 95% response of 21.9 and 15.7, respectively. To examine the stability of resistance, the responses of adult males to chlorpyrifos and cypermethrin were tested repeatedly over 3 yr and results were compared by chi-square analysis. Resistance levels showed significant yearly variation in each of the 50 and 95% resistance ratios, but only significant insecticidal variation at the 50% level. Treatment with piperonyl butoxide before insecticides restored susceptibility to only 1 of 4 insecticides tested on adult males, suggesting that a monooxygenase resistance mechanism coexists with other mechanisms in this strain. Biochemical assays confirmed that this strain possessed both elevated levels of cytochrome P450 monooxygenase (in the adult male stage) and esterase activity (in 1st instars), compared with a standard susceptible strain of German cockroach. Native esterases from 1st instars in the field-collected strain differed electrophoretically from those in the susceptible strain.