Life Table and Sensitivity Analysis as Fitness Evaluation Method of Fenpyroximate and Pyridaben Resistant Twospotted Spider Mite (Tetranychus urticae Koch)

Fitness associated with pesticide resistance was assessed in twospotted spider mites, Tetranychus urticae Koch, using life table analysis. Two strains resistant to fenpyroximate (FR) and pyridaben (PR), and one susceptible strain (S) were included in this study. Two reciprocal crosses (FR♂xS♀ and PR♂xS♀) were established by conventional crossing procedure. Intrinsic rate of natural increase (r_m) was used as a comparative parameter of reproductive fitness among 3 parent strains (FR, PR, and S) and two reciprocal crosses. Sensitivity analysis was performed to evaluate significances of biological factors contributing to r_m. The r_m values were not significantly different from each other, with an exception of FR♂xS♀ cross and ranged from 0.250 to 0.274 per day. Sensitivity analysis revealed that birth rate (b) and mortality (μ) effects could account for the effect on r_m in the two resistant strains. Contributions of b and μ to r_m was markedly different in two resistant strains; high contribution in b and low in μ. Age at the first reproduction (t) and age at the last reproduction (t_ω) made roughly equal contributions to r_m between the strains and the crosses. This study clearly showed that how r_m was affected by various biological factors and provided a basic analytical tool for pesticide resistant management.