Validamycin Inhibits the Synthesis and Metabolism of Trehalose and Chitin in the Oriental Fruit Fly, Bactrocera dorsalis (Hendel)

SIMPLE SUMMARY: Validamycin is a strong competitive trehalase inhibitor that has long been used as an anti-fungal antibiotic to target trehalose hydrolysis. To clarify whether validamycin can also be adopted for the management of Bactrocera dorsalis (Diptera, Tephritidae), the effects of validamycin injection on the synthesis and metabolism of trehalose and chitin were evaluated. The results showed that validamycin injection significantly inhibited the synthesis and metabolism of trehalose and chitin, thus leading to high mortality and deformity rates. These findings imply that validamycin can be considered as a promising potential insecticide for the management of B. dorsalis. ABSTRACT: The oriental fruit fly, Bactrocera dorsalis (Hendel), is a notorious invasive pest that has raised concerns worldwide. Validamycin has been demonstrated to be a very strong inhibitor against trehalase in a variety of organisms. However, whether validamycin can inhibit trehalase activity to suppress trehalose hydrolysis and affect any other relevant physiological pathways in B. dorsalis remains unknown. In this study, the effects of validamycin injection on the synthesis and metabolism of trehalose and chitin were evaluated. The results show that validamycin injection significantly affected trehalase activity and caused trehalose accumulation. In addition, the downstream pathways of trehalose hydrolysis, including the synthesis and metabolism of chitin, were also remarkably affected as the expressions of the key genes in these pathways were significantly regulated and the chitin contents were changed accordingly. Intriguingly, the upstream trehalose synthesis was also affected by validamycin injection due to the variations in the expression levels of key genes, especially BdTPPC1. Moreover, BdTPPC1 was predicted to have a binding affinity to validamycin, and the subsequent in vitro recombinant enzyme activity assay verified the inhibitory effect of validamycin on BdTPPC1 activity for the first time. These findings collectively indicate that validamycin can be considered as a promising potential insecticide for the management of B. dorsalis.