Role of digestive enzymes in the adaptation of Frankliniella occidentalis to preferred and less‐preferred host plants

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AbstractThe western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is an important invasive pest that causes serious damage to vegetables in China. Changes in digestive enzyme activities (α‐amylase, trypsin, and tryptase) and gene expression levels of F. occidentalis were examined after they were transferred to kidney bean, a preferred host, or broad bean, a less‐preferred host. The results showed that α‐amylase and trypsin activities initially decreased in both nymphs and adults after transfer to kidney bean or broad bean plants and they were the lowest in the F1 generation. The α‐amylase and trypsin activities were significantly different among the tested generations. The tryptase activities in the second instars fed on kidney bean plants were not significantly different from those of the controls in nymphs at all three generations, whereas they increased when fed on broad bean plants. Most digestive enzyme genes in both the nymph and adult thrips showed similar changes, decreasing with transfer to kidney bean plants and increasing on broad bean plants. However, the expression levels of the trypsin gene FoTRYP‐1 and the tryptase gene FoTPSB2 in the second instars fed on broad bean and kidney bean plants, respectively, were not significantly different from those of the controls. The expression levels of the four digestive enzyme genes were significantly higher in broad bean than in kidney bean plants. These results indicate that F. occidentalis can adjust its digestive enzyme activities and gene expression levels after being transferred to host plants for which its preference differs and that the changes depend on the specific enzyme, thrips generation, and developmental stage. Findings from this study would provide a basis for further studies to reveal the physiological and ecological bases of the wide host range and strong host adaptability of F. occidentalis.