Sublethal Effects of Imidacloprid on the Population Development of Western Flower Thrips Frankliniella occidentalis (Thysanoptera: Thripidae)

The Western flower thrips (WFT, Frankliniella occidentalis) is a global polyphagous pest that is often dependent on chemical control. Imidacloprid has been a commonly used chemical insecticide for effective control of WFT. Low concentrations of insecticides can have sublethal effects on individual insects. However, no more information is known about the effects of exposure at low concentrations of imidacloprid on WFT. Here, we evaluated the effects of imidacloprid at sublethal concentrations on WFT population growth parameters. We first exposed the parental generation to LC(10) (56.8 mg/L) and LC(25) (79.2 mg/L) concentrations of imidacloprid. We then quantified various parameters related to the development, survival, and fecundity of the F(1) generation also exposed to these same concentrations. The development time of the treatment groups exposed to imidacloprid was significantly shorter than the control group, and the net reproductive rate (R(0)) was significantly higher for treatment groups than for the control group. For both variables, there was no significant difference between LC(10) and LC(25) exposure. The generational survival rate was significantly higher for the control group, followed by the LC(10) treatment group and then the LC(25) treatment group. However, the opposite was true for fecundity and intrinsic rate of increase (r(m)) of WFT. In summary, exposure to low concentrations of imidacloprid was positive for the population development of WFT, which may contribute to the development of insecticide resistance and cause resurgence in WFT populations.