Abstract: In this study, we aimed to clarify the effects of imidacloprid on interspecific competition between thripsFrankliniella occidentalis andF. intonsa by recording the developmental and fecundity parameters of both species in a competition experiment under laboratory conditions. The LC₅₀ concentrations of imidacloprid in both species were measured by dipping feeding method. Both species were reared on beans in the same cage with a starting ratio of 1∶1 under pesticide stress at the predetermined LC₅₀ concentration on 2nd instar larvae ofF. intonsa. The results showed that there was a consistently higher proportion of females in both species from 25 d to 150 d, with the female excess being higher inF. occidentalisthan in that inF. intonsa underimidacloprid stress (P<0.05). The developmental duration of the immature stages in both species were significantly shorter than in the control, and F. occidentalis developed consistently faster thanF. intonsa(P<0.05). The population survival rate and the longevity of male and femaleadults ofF. occidentalis were slightly higher than that ofF. intonsa, but the difference was not significant (P>0.05). The net reproductive rate (R₀), the intrinsic rate of increase (r_m) and the growth rate (λ) ofF. occidentaliswere significantly higher than that ofF. intonsa. Thelongevity of both male and female adults, the mean length of generation (T) and populationdoubling time (DT) of both species in the pesticide treatments were significantly shorter (P<0.05) than that in control. Average fecundity, R₀,r_m and λ inF. occidentalis were significantly higher than that in control (P<0.05), while average fecundity, R₀,T and DTof F. intonsa were significantly lower. Overall,F. occidentalis was more adaptable thanF. intonsato imidacloprid stress, with females being more adaptable than males for both species. Imidacloprid stress is one of the key reasons for the accelerated replacement ofF. intonsaby F. occidentalis populations.

Key words: water utilization, northwest Loess Plateau semi-arid area, whole field soil-plastic mulching, spring wheat, photosynthesis