Objective This paper investigates the effects of leucokinin (LK) neuropeptide and its receptor on growth of Hyphantria cunea.

Method An in vitro prokaryotic expression system was developed for synthesize of LK/LKR dsRNA. The 4th instar larvae of Hyphantria cunea were fed with dsRNA-expressing bacteria. The food intake, body mass and developmental duration were measured and recorded. Subsequently, the 4th instar larvae of Hyphantria cunea were injected with short LK1 and LK2 peptide. Digestive enzyme activities, trehalose, glycogen, and glucose content in the midgut and fat body were detected after 72 h. And the relative expression level of related genes was detected using RT-qPCR technology.

Result Bacteria-mediated RNAi effectively silenced LK and LKR genes. It affected the food intake of the 4th instar larvae of Hyphantria cunea within 48 h, but it was not significant (P > 0.05). It led to a significant increase in relative growth rate within 48 h, and a delay in developmental duration. It led to an increase in feeding amount (P > 0.05) and a significant increase in relative accumulation growth rate within 48 h, and delayed the development time. After injection of LKs short peptide, the feeding amount and relative accumulation growth rate of 4th instar larvae of Hyphantria cunea were significantly reduced, and the water content of feces was significantly increased at 24 h after injection, but the water content of larvae was not significantly different. Further studies showed the activities of α-amylase in the midgut, and lipase, α-amylase, trypsin, trehalase in the fat body were significantly enhanced at 72 h after injection. The content of glycogen in the midgut decreased significantly. The content of glycogen and trehalose in the fat body increased significantly, while the content of glucose was significantly reduced. The expression level of LIP genes (excluding LK1 group in the fat body), and amy-1 and amy-2 genes significantly increased in the midgut and fat body. The expression level of Tre1, Tre2 and Tret1 genes increased significantly in the midgut. The expression level of Tre1 (excluding LK2 group) and Tre2 decreased, while the expression level of Tret1 (LK2 group) significantly increased in the fat body.

Conclusion This study reveals that LK is involved in regulating feeding, energy metabolism and growth in Hyphantria cunea, providing a theoretical basis for the development of green insecticides to control Hyphantria cunea.