Ecdysis Triggering Hormone Signaling (ETH/ETHR-A) Is Required for the Larva-Larva Ecdysis in Bactrocera dorsalis (Diptera: Tephritidae)

Abstract

Insects must undergo ecdysis for successful development and growth, and the ecdysis triggering hormone (ETH), released by the Inka cells, is a master hormone in this process. In this study, we determined the sequence of the ETH precursor and receptors in an agriculturally important pest insect, the oriental fruit fly <i>Bactrocera dorsalis</i> (Hendel). We identified two functionally distinct splice receptor isoforms: BdETH-R-A and BdETH-R-B, and when expressed in Chinese hamster ovary (CHO-WTA11) cells, they exhibited a high sensitivity to the two mature peptides BdETH1 and BdETH2. The <i>BdETH</i> transcript was detected in the tracheal tissue of the larvae. Inka cells were identified with immunohistochemical antibody staining against <i>Drosophila melanogaster</i> ETH1, and <i>in situ</i> hybridization with specific DNA probes. Selective RNA silencing of <i>BdETH</i> or <i>BdETH-R-A</i>, but not of <i>BdETH-R-B</i>, caused developmental failure at ecdysis. The dsRNA-treated larvae displayed tracheal defects and could not shed the old cuticle followed by death. Our results demonstrated that BdETH, via activation of BdETH-R-A but not ETH-R-B, plays an essential role in regulating the process of larva-larva ecdysis in <i>B. dorsalis</i>.