Sublethal effects of spinetoram and azadirachtin on development and reproduction of Frankliniella occidentalis (Pergande).

Abstract

To evaluate the sublethal effects of spinetoram and azadirachtin on western flower thrips, Frankliniella occidentalis, leaf dipping method was used to determine their sublethal concentrations (LC25) on the 2nd instar nymph, and their influences on development and reproduction of F. occidentalis were studied. The results showed exposure of sublethal concentrations of spinetoram and azadirachtin to F. accidentalis had different degrees of effects on this insect pest. Under bisexual reproduction, the LC25 spinetoram had no significant influences on pre-oviposition period, female adult longevity and fecundity, but male adult longevity was significantly shorter than the control. The LC25 azadirachtin significantly reduced fecundity and prolonged pre-oviposition period. Under parthenogenesis, the LC25 spinetoram and azadirachtin extended the pre-oviposition duration, whereas the LC25 azadirachtin shortened the female adult longevity and significantly decreased fecundity. The LC25 spinetoram and azadirachtin had different influences on developmental duration of each stage of next generation. The immature stage in treatment group of the LC25 spinetoram was shorter than that in treatment group of the LC25 azadirachtin, under bisexual reproduction or parthenogenesis. Intrinsic rate of increase (rm) and finite rate of increase (λ) of population treated by the LC25 spinetoram were higher than those of the control, whereas the rm, R0, and λ of population treated by the LC25 azadirachtin were lower than those of the control. The findings indicated that the effects of the LC25 spinetoram and azadirachtin on the development and reproduction of F. accidentalis were different. The LC25 spinetoram had certain stimulating effect, whereas the LC25 azadirach-tinon had significant inhibitory effect. Two biopesticides' influences were related with the reproductive patterns of F. accidentalis.