Abstract:

【Aim】 Spinetoram is one of the candidate pesticides most used for controlling the western flower thrips, Frankliniella occidentalis, on vegetables. This study aims to assess the effects of multigeneration spinetoram stress on F. occidentalis. 【Methods】 The 2nd instar nymphs of F. occidentalis were screened for six generations with LC₂₅ dosage of spinetoram by the leaf dipping method, and the insecticide sensitivity and detoxification enzyme activities in the nymphs were determined. The agestage twosex life table was used to analyze the effect of LC₂₅ dosage of spinetoram on the life table parameters of F. occidentalis offspring (F₇). 【Results】 After the 2nd instar nymphs of F. occidentalis were selected with LC₂₅ dosage of spinetoram for six generations, the resistance ratio increased to 6.4 folds as high as that of the control treated with water. CarE and GSTs in the day-2 2nd instar nymphs of F₆ generation were significantly activated, with their activities 1.26 and 1.21 folds as high as those of the control, while MFOs and P450s were significantly inhibited, with their activities only 54.00% and 51.78% of those of the control, respectively. When the 2nd instar nymphs of F. occidentalis were selected with LC₂₅ dosage of spinetoram for six generations, the longevity (19.33 d) and fecundity (69.80 eggs) of female adult significantly decreased as compared to those of the control (21.60 d and 83.17 eggs, respectively), the female adult longevity (16.82 d) and male adult longevity (8.29 d) of F₇ generation were also significantly shortened as compared to those of the control (20.28 d and 10.86 d, respectively), the fecundity of F₇ generation (59.23 eggs laid per female) extremely significantly decreased as compared to that of the control (76.96 eggs laid per female), but the female to male sex ratio (2.28) significantly increased as compared to that of the control (1.03). The net reproductive rate (R₀), intrinsic rate of increase (r) and finite rate of increase (λ) in F₇ generation of F. occidentalis after selection with LC₂₅ dosage of spinetoram for six generations had no significant change. 【Conclusion】 The resistance of F. occidentalis to spinetoram

increases slowly within six generations under selection by LC₂₅ dosage of spinetoram. Spinetoram stress not only causes significant changes in the detoxification enzyme ctivities in F. occidentalis, but also inhibits its development and reproduction.

Key words: Frankliniella occidentalis, spinetoram, detoxification enzyme, insecticide screening, insecticide resistance