DIFFERENCES IN RESISTANCE TO FENVALERATE AND CYHALOTHRIN AND INHERITANCE OF KNOCKDOWN RESISTANCE TO FENVALERATE IN HELICOVERPA-ARMIGERA

A resistant strain of Helicoverpa armigera selected by cyhalothrin was used to investigate the relative importance of knockdown resistance ( kdr) for different levels of resistance to cyhalothrin and fenvalerate and the inheritance of kdr to fenvalerate. Pretreatment of piperonyl butoxide (PBO) decreased the resistance ratios from 30.6- to 5.0-fold for cyhalothrin and from 337.0- to 38.0-fold for fenvalerate. Electrop hysiological studies showed that kdr ratios were 10.7- and 95.8-fold t o cyhalothrin and fenvalerate, repectively, at EC50 of burst discharge of neuromuscle preparation, and were 15.0- and 507.2-fold to cyhaloth rin and fenvalerate, respectively, at EC50 Of blocked neuromuscular tr ansmission. It was indicated that the difference in kdr to fenvalerate and cyhalothrin is the main reason for the difference in resistance l evel between the two pyrethroids in the resistant strain of H. armiger a. Analysis of probit lines from F-1 reciprocal crosses indicated that kdr to fenvalerate was inherited autosomaly as an incompletely recess ive factor. The degrees of dominance were -0.74 and -0.78, based on bu rst discharge and blocked transmission, respectively, with pooled F-1 generations. chi 2 analysis of knockdown responses of backcrossed offs pring indicated that the resistance might be controlled by one major g ene. Cross-resistance to aconitine was detected in resistant strain af ter applying PBO, indicating that sodium channels are different in the resistant and susceptible strains of H. armigera. (C) 1998 Academic P ress.