Halloween genes as optimal RNAi-based targets for controlling the cigarette beetle, Lasioderma serricorne

As an important insect endohormone, 20-hydroxyecdysone (20E) plays a key role in regulating the metamorphosis and development of insects, and the Halloween genes are involved in 20E biosynthesis. However, the function of Halloween genes in Lasioderma serricorne, a major pest of stored products worldwide, remains unknown. Here, five Halloween genes from L. serricorne, namely LsCYP307A1, LsCYP302A1, LsCYP306A1, LsCYP315A1, and LsCYP314A1, were cloned and identified. All of Halloween genes were primarily expressed in the 4th instar larvae or prepupae. LsCYP307A1, LsCYP306A1, and LsCYP314A1 were mainly expressed in the thorax, while LsCYP302A1 and LsCYP315A1 were universally expressed in the midgut of the peripheral tissues. RNA interference (RNAi) results showed that silencing the Halloween genes significantly reduced the 20E titer, prolonged the pupation time, and led to high mortality in the process of pupation. Hematoxylin-eosin staining results suggested that knocking down the Halloween genes inhibited the degradation and apolysis of the old cuticle. Furthermore, silencing the Halloween genes led to significant downregulation of the expression level of the 20E signaling pathway and chitin metabolism pathway genes, while the RNAi phenotype could be rescued with the application of exogenous 20E. This study concluded that the manipulation of Halloween genes can inhibit the development of L. serricorne via controlling 20E synthesis, and thus Halloween genes could be useful molecular targets for controlling pests.