Effects of a sublethal concentration of avermectin on the development and reproduction of citrus red mite, Panonychus citri (McGregor) (Acari: Tetranychidae)

To assess the total effects of avermectin and for rational application, the effects of a sublethal concentration (the LC20 was chosen as a representative) of avermectin on the development and reproduction of the citrus red mite, Panonychus citri (McGregor), were evaluated at 26 +/- 1 degrees C, 70-75% relative humidity and a photoperiod of 14 : 10 h light : dark in the laboratory. The results showed that the sublethal dose of avermectin had no significant effect on the hatching rate of eggs and the emergence rate of the nymphs. However, after exposure to avermectin, females of the parental generation (F0) and progeny (F1 and F2) produced fewer eggs than did the control females. The larval and nymphal developmental periods were also affected significantly by exposure to avermectin. Furthermore, the pre-oviposition period as well as the adult longevity was shortened, resulting in a decrease of the mean generation time. Generally, the mites exposed with sublethal concentration of avermectin during the nymphal stages showed positive effects on population increase [i.e. higher intrinsic rate of increase (rm), net reproductive rate (R0), and finite rate of increase () values, but shorter population doubling times (Dt)], whereas the mites treated during the adult stages had negative effects on population increase (i.e. lower rm, R0, and values, longer Dt). Such effects were more obvious at the F2 generation than at the F1 generation in both treatments.