Mechanism underlying avermectin-mediated acceleration of interspecific competition between Frankliniella occidentalis and Megalurothrips usitatus.

Frankliniella occidentalis (Pergande) and Megalurothrips usitatus are invasive and native thrips species, respectively, that cause serious damage to bean plants. We investigated the effects of avermectin on the interspecific competition between these thrips species and the underlying metabolic mechanism. The results showed that F. occidentalis was more resistant to avermectin than M. usitatus, and it subsequently replaced M. usitatus with or without avermectin treatment. This replacement under avermectin stress occurred after one generation, which was one less than that under no avermectin stress. The P450 activity in F. occidentalis was significantly higher than that in the control at any time point, including F1 generation. In M. usitatus, it was significantly higher than that in the control over three short time intervals after avermectin treatment. The P450 activity in M. usitatus was significantly higher than that in F. occidentalis at 72 h, but an opposite effect was observed in the F1 generation. Although CYP6-3 expression in both F. occidentalis and M. usitatus was generally significantly inhibited, it was substantially upregulated at 72 h in F. occidentalis and in the F1 generation of M. usitatus respectively. Under avermectin stress CYP6-3 expression was significantly lower in M. usitatus than in F. occidentalis at 72 h, whereas it was the opposite at other time points. The two thrips species exhibited enhanced metabolic detoxification of pesticides via increased activity of detoxifying enzyme. This resistance was persistent in F. occidentalis but only temporary in M. usitatus. Our results suggest that avermectin stress accelerates the competitive replacement of M. usitatus by F. occidentalis. [ABSTRACT FROM AUTHOR]