Abstract
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 LC10 (56.8 mg/L) and LC25 (79.2 mg/L) concentrations of imidacloprid. We then quantified various parameters related to the development, survival, and fecundity of the F1 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 (R0) was significantly higher for treatment groups than for the control group. For both variables, there was no significant difference between LC10 and LC25 exposure. The generational survival rate was significantly higher for the control group, followed by the LC10 treatment group and then the LC25 treatment group. However, the opposite was true for fecundity and intrinsic rate of increase (rm) 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.
Highlights
The Western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is one of the most destructive and economically important pests of vegetables, fruit, and ornamental crops [1]
Exposure of WFT to the low concentrations of imidacloprid shortened the duration of the first instar, second instar, and prepupal stages when compared with the control group (F = 10.607, df = 2732, Insects 2018, 9, x p = 0.011; F = 21.053, df = 2669, p = 0.002; F = 7.938, df = 2645, p = 0.021, respectively) (Table 1)
There was no significant difference in developmental time from egg to to adult between the two treatment groups exposed to imidacloprid (LC 10 = 9.57 d and LC25 = 9.38 d), adult between the two treatment groups exposed to imidacloprid (LC10 = 9.57 d and LC25 = 9.38 d), but both groups had significantly shorter developmental times from egg to adult than the control but both groups had significantly shorter developmental times from egg to adult than the control treatment group (10.31 d; F = 51.814, df = 2,618, p < 0.001)
Summary
The Western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is one of the most destructive and economically important pests of vegetables, fruit, and ornamental crops [1]. WFT is native to Western North America. They have attained a worldwide distribution in the past 30 years, and been reported as an invasive pest [1,4]. In China, the WFT was first reported in Yunnan Province in 2000 and in Beijing in 2003 [5]. It has spread rapidly to most areas of China and has caused severe economic damage [4,6].
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