Cross resistance, inheritance and fitness advantage of cyetpyrafen resistance in two-spotted spider mite, Tetranychus urticae.

ABSTRACT

Cyetpyrafen belonging to mitochondrial electron transport inhibitors of complex II (METI II) has been widely applied to manage pest mites in China. To investigate the adaption of Tetranychus urticae in the evolution of cyetpyrafen resistance, a study of cross resistance, mode of inheritance and fitness comparison of resistance using indoor cyetpyrafen resistant strain (resistance ratio, RR > 2, 000-fold) was executed. Cyet-R showed serious cross resistance to cyenopyrafen (>2500-fold) and cyflumetofen (~190-fold). The number of resistant genes was evaluated via chi-square (χ2) test and the concentration-response curve regarding goodness-of-fit between observed and the expected mortality. The LC50s of F1RS (Cyet-R♀ × Tu-YN♂) and F1SR (Tu-YN♀ × Cyet-R♂) were 3126.30 mg/L and 2743.97 mg/L, respectively, without significance, suggesting autosomal inheritance. The degree of dominance (D) values of F1RS and F1SR ranged between 0 and 1, revealing an incompletely dominant inheritance in the tested population of Tetranychus urticae. Plots of concentration-response data for the orthogonal backcross and reverse backcross progenies showed a significant deviation from the expected lines, pointing out a polygenic inheritance. Besides, lifetable analysis showed a fitness advantage of Cyet-R with a significantly decreased adult preadult period and significantly increased total fecundity. This study suggested that cyetpyrafen resistance against T. urticae was inherited as autosomal, incompletely dominant and multigenetic and characterized with serious cross resistance and fitness advantage. Therefore, rational application and preventive strategy should be considered to sustain the efficacy of cyetpyrafen against T. urticae.