[Sublethal effects of fenpropathrin and avermectin on Panonychus citri (Acari: Tereanychidae).]

A leaf disc bioassay was employed to examine the effects of fenpropathrin and avermectin with a sublethal concentration of LC₂₀ on the development and reproduction of F₀, F₁ and F₂ generations by means of life tables. The results showed that after the treatment of fenpropathrin at the sublethal concentration, the number of eggs laid per female significantly increased in F₀ generation, the pre-oviposition duration was significantly shortened and the female ratio of offspring significantly increased both in F₁ and F₂ generations. The intrinsic rate of increase (r_m) and finite rate of increase (λ) values all increased, and the generation time (T) and population doubling time (Dt) were shortened in F₁ and F₂ generations, with significant difference observed between F₂ generations and the control. After exposure to avermectin, the number of eggs laid per female significantly decreased in F₀ generation, and progeny (F₁ and F₂) also produced fewer eggs than the control, while the female ratio of offspring increased both in F₁ and F₂ generations and the pre-oviposition period was significantly shortened. The r_m and λ values all increased, and the T and Dt were shortened in F₁ and F₂ generations. Such effects were more obvious on the F₂ generation than the F₁ generation. Generally, the effects of fenpropathrin and avermectin with a sublethal concentration of LC₂₀ were not exactly the same on P. citri. Fenpropathrin could promote the development of the contemporary population, while avermectin had certain inhibition on the contemporary population, but both played a certain role in facilitating the development of future populations, which was of significance in developing integrated pest management strategies.