Modulating expression of Frankliniella occidentalis glutathione S-transferase genes to adapt to host shifts

Western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is an important global pest of vegetables and ornamental crops that has strong host adaptability. Glutathione S-transferases (GSTs) detoxify and metabolise toxic plant allelochemicals during insect adaptation to host plant defence responses. However, how genes of different GST subfamilies affect adaptation of F. occidentalis after a host shift remains unclear. In this study, thrips were shifted from kidney bean pods to broad bean plants and kidney bean plants. Expression levels of the GST genes were determined in the second instar larvae and adult females of F₁, F₂, and F₃ generations. Four GST genes were cloned and identified, namely FoGSTd1, FoGSTs1, FoGSTt1, and FoGSTe1 belonging to the delta, sigma, theta, and epsilon subfamilies, respectively. Expression profiles of these four genes differed at each developmental stage of F. occidentalis, and the degree of FoGSTs1 expression change after the transfer to the kidney bean plants or broad bean plants were the strongest. When F. occidentalis adult females transferred to kidney bean plants or broad bean plants were fed with anti-FoGSTs1 double-stranded RNA (dsRNA), FoGSTs1 expression was significantly downregulated, and GST enzyme activity was significantly inhibited. Further, RNA interference-mediated knockdown of FoGSTs1 significantly decreased the survival rate of F. occidentalis female adults on kidney bean plants and broad bean plants. These results indicate that FoGSTs1 plays an important role in affecting the adaptation of F. occidentalis after host shift.