Abstract
Competitive interactions between species can be mitigated or even reversed in the presence of anthropogenic influences. The thrips species Frankliniella occidentalis and Thrips tabaci are highly invasive and damaging agricultural pests throughout the world. Where the species co-occur, one species tends to eventually predominate over the other. Avermectin and beta-cypermethrin are commonly used insecticides to manage thrips in China, and laboratory bioassays demonstrated that F. occidentalis is significantly less susceptible than T. tabaci to these insecticides. In laboratory cage trials in which both species were exposed to insecticide treated cabbage plants, F. occidentalis became the predominant species. In contrast, T. tabaci completely displaced F. occidentalis on plants that were not treated with insecticides. In field trials, the species co-existed on cabbage before insecticide treatments began, but with T. tabaci being the predominant species. Following application of avermectin or beta-cypermethrin, F. occidentalis became the predominant species, while in plots not treated with insecticides, T. tabaci remained the predominant species. These results indicate that T. tabaci is an intrinsically superior competitor to F. occidentalis, but its competitive advantage can be counteracted through differential susceptibilities of the species to insecticides. These results further demonstrate the importance of external factors, such as insecticide applications, in mediating the outcome of interspecific interactions and produce rapid unanticipated shifts in the demographics of pest complexes.
Highlights
Numbers in some regions where the invasive F. occidentalis has become predominant[15]
The proportions of F. occidentalis adults differed between the insecticide treatments and the control treatment following the first insecticide application, and this difference increased over time, with the proportion of F. occidentalis exceeding 80% by the end of the trial. These results indicate that applications of avermectin and beta-cypermethrin reduced the abundance of T. tabaci relative to the abundance of F. occidentalis (Fig. 3)
Our results demonstrate that T. tabaci is competitively superior to F. occidentalis on cabbage foliage in the absence of insecticides
Summary
Numbers in some regions where the invasive F. occidentalis has become predominant[15]. It is possible that external factors determine which species competitively excludes the other from a particular region. One factor that can mediate competitive interactions is the use of insecticides in cropping systems. Research has demonstrated that differential susceptibility to insecticides may increase the likelihood of one species being replaced by another, driving changes in population demographics[17,18,19]. Two of the most commonly applied insecticides for management of thrips in China are avermectin and beta-cypermethrin[15]. Using both laboratory and field experiments, we investigated interspecific differences in susceptibility to these insecticides and determined if differential susceptibility could explain the observed changes in thrips demographics
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