| Summary: | Dusky-like (Dyl) is a transmembrane protein containing a zona pellucida domain. Its physiological roles during metamorphosis have been well explored in <i>Drosophila melanogaster</i> and have also been documented in <i>Tribolium castaneum</i>. However, Dyl has undergone a functional shift between Diptera and Coleoptera insects. Further investigation of Dyl in other insects will be helpful to further clarify its function in insect growth and development. <i>Henosepilachna vigintioctopunctata</i> is an important Coleoptera that causes enormous economic losses in agriculture in China. In this study, we found that the expression of <i>Hvdyl</i> was detectable in embryos, larvae, prepupae, pupae, and adults. We knocked down <i>Hvdyl</i> in third- and fourth-instar larvae and pupae with RNA interference (RNAi). RNAi of <i>Hvdyl</i> mainly caused two phenotypic defects. Firstly, the growth of epidermal cellular protuberances was suppressed. Injection of ds<i>dyl</i> (double-stranded <i>dusky-like</i> RNA) at the third-instar larval stage truncated the scoli throughout the thorax and abdomen and shortened the setae on the head capsules and mouthparts of the fourth-instar larvae. Introduction of ds<i>dyl</i> at the third- and fourth-instar stages led to misshapen pupal setae. The setae were shortened or became black nodules. Treatment with ds<i>dyl</i> at the larval and pupal stages resulted in deformed adults with completely suppressed wing hairs. Moreover, the knockdown of <i>Hvdyl</i> at the third-instar stage caused deformed larval mouthparts at the fourth-instar period. As a result, foliage consumption was inhibited, and larval growth was slowed. The results indicate that Dyl is associated with the growth of cellular protuberances throughout development and with the formation of the cuticle in <i>H. vigintioctopunctata</i>.
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