BEHAVIORAL AND PHYSIOLOGICAL RESISTANCE TO INSECTICIDES IN THE GERMAN-COCKROACH (DICTYOPTERA, BLATTELLIDAE) - AN EXPERIMENTAL REEVALUATION

Although physiological resistance to pesticides has been demonstrated in German cockroaches, Blattella germanica (L.), behavioral resistance has not been shown clearly. To test for the possible development of b ehavioral resistance, choice-test experiments were done to determine w hether adult males and females from physiologically resistant and susc eptible strains differed in avoidance of three emulsifiable formulatio ns (chlorpyrifos, cypermethrin, and chlordane). Physiological resistan ce was verified by estimation of LC50s. Within 6 h, each cockroach cho se between an untreated and a treated harborage. In the resistant stra in, both sexes avoided harborages treated with cypermethrin and surviv ed the choice tests, but more females than males avoided harborages tr eated with chlorpyrifos and survived. In the susceptible strain, neith er sex avoided harborages treated with cypermethrin or chlorpyrifos, a nd most died. The physiologically resistant strain was more resistant to chlorpyrifos and cypermethrin than was the susceptible strain, with females generally having higher LC50s. However, in choice tests with chlordane in which physiological resistance levels were similar betwee n the strains, the strains did not differ in avoidance of treated harb orages or survivorship. Avoidance of treated harborages may be facilit ated by high levels of physiological resistance, but we detected no be havioral resistance traits. High levels of physiological resistance pe rmitted cockroaches to absorb an amount of pesticide that led to detec tion and subsequent avoidance of treated harborages. Results of our st udy suggest that previous research on insects has not demonstrated the evolution of stimulus-dependent behavioral resistance in field popula tions exposed to pesticides.