Identification and functional characterization of the sulfakinin and sulfakinin receptor in the Chinese white pine beetle Dendroctonus armandi

The sulfakinin (SK) is an important signal molecule. As a neuromodulator, it mediates a variety of behavioral processes and physiological functions in invertebrates through the interaction with G-protein-coupled receptors (GPCRs). However, there is no report on the functional role of SK in the Chinese white pine beetle, Dendroctonus armandi. We have cloned and characterized SK and SKR genes in the D. armandi and carried out bioinformatics predictions on the basis of the deduced amino acid sequences, which are very similar to those from Dendroctonus ponderosa. The expression levels of the two genes were different between male and female adults, and there were significant changes in different developmental stages, tissues, and between starvation and following re-feeding states. Additionally, RNA-interference (RNAi) using double-stranded RNA to knock down SK and SKR reduced the transcription levels of the target genes and increased their body weight. In parallel, injection of SK caused a significant reduction in body weight and increase in mortality of D. armandi and also led to an increase in trehalose and a decrease in glycogen and free fatty acid. The results show that the SK signal pathway plays a positive and significant role in feeding regulation and provides a potential molecular target for the control of this pest.