Assessment of Sublethal Effects of Clofentezine on Life-table Parameters in Hawthorn Spider Mite (Tetranychus viennensis)

Abstract

A leaf disc bioassay was employed in the laboratory to assess the population responses of Tetranychus viennensis Zacher to clofentezine at three concentrations (LC₁₀, LC₂₅ and LC₅₀) in three successive generations. Life-table parameters were calculated in each acaricide exposure regime and compared by jackknife procedures. Clofentezine treatments in the juvenile stages significantly delayed development of the mites, and this delay increased with increasing dose but decreased as the mites developed. Exposure to clofentezine reduced the net reproduction rate (R₀) in a concentration-dependent manner. The LC₅₀ treatment had strong effects on the hatchability of eggs produced by surviving females. Hatch rate dropped from 0.83 in the untreated control to 0.51 in the third generation. When exposed to constant concentrations of clofentezine in three successive generations, the intrinsic rate of increase and R₀ of the mites decreased significantly, but they increased significantly when exposed to decreasing concentrations. Unexposed offspring of the exposed mother also displayed increases in R₀ and the jackknife procedures indicated no significant differences in R₀ between LC₁₀ and LC₂₅ offspring and their mothers vs. the control, while R₀ in unexposed LC₅₀ offspring was significantly higher than their mother’s, but lower than that in the control. These changing patterns of r_m reveal that acaricide effects at the population level strongly depend on the life-history characteristics of T. viennensis and the chemical mode of action.