RNA interference targeting tyrosine hydroxylase and dopa decarboxylase inhibits the reproduction and survival in the small brown planthopper Laodelphax striatellus: A promising strategy for pest control.

The small brown planthopper Laodelphax striatellus is a serious insect vector in rice and causes substantial economic losses. Dopamine (DA) plays an important role in the multiple physiological and behavioral processes of insects, and tyrosine hydroxylase (TH) and dopa decarboxylase (DDC) are crucial enzymes in regulating DA synthesis. Although numerous studies have investigated the roles of TH and DDC in various insects, their functions in rice planthoppers remain poorly understood. Here, we cloned LsTH and LsDDC from L. striatellus. LsTH was predominantly expressed at the late stage of 3rd-5th instar nymphs, and LsDDC was most highly expressed at the egg stage. LsTH and LsDDC exhibited the higher expression levels in the wing and cuticle compared to other tissues. RNA interference (RNAi)-mediated silencing of LsTH and LsDDC significantly shortened the oviposition period, reduced the fecundity, and inhibited egg hatchability and development. Moreover, silencing of LsTH and LsDDC significantly downregulated the expression levels of vitellogenin (LsVg) in the fat body and ovary of L. striatellus, and the expressions of Vg receptor (LsVgR) in the ovary, as well as decreased the transcript levels of the genes involved in juvenile hormone (JH) and 20-hydroxyecdysone (20E) signaling pathways. In addition, RNAi targeting LsTH and LsDDC markedly reduced the survival rates of L. striatellus. This study demonstrates the critical roles of LsTH and LsDDC in the reproduction and survival of L. striatellus, suggesting their potential as promising targets for designing pest control strategies.