An insulin-like peptide mediates trehalose storage in the western tarnished plant bug, Lygus hesperus

Insulin signaling controls many physiological processes in insects, and it has a demonstrated role in cellular uptake of circulating sugars. Although model insects have pioneered much of our understanding of insulin signaling, high throughput genetic sequencing has enabled opportunities for the physiological study of less explored insect species. Lygus hesperus, the western tarnished plant bug, is a significant agricultural pest of numerous crops and recent efforts have focused on molecular approaches for identifying new pest management strategies. In this work, three insulin-like peptides (LhILP1, LhILP2, and LhILP3) were characterized from the transcriptome of L. hesperus. LhILP1 and LhILP2 structurally resemble classic insulin-like peptides while LhILP3 resembles arthropod Insulin-like Growth Factors (aIGFs). All three LhILPs were primarily expressed in the head, and were observed throughout development. We examined their function by observing clearance rates of injected trehalose from the hemolymph in adult L. hesperus males following RNAi knockdown of the respective LhILPs. Untreated males cleared the trehalose within 6 h and showed a corresponding increase in glycogen content. While knockdown of LhILP1 did not impact clearance rate, knockdown of LhILP2 prevented clearance of circulating trehalose and glycogen accumulation. Knockdown of LhILP3 also prevented trehalose clearance, but this appears to be influenced by co-knockdown of LhILP2, rather than a direct effect. Head ligation stopped the release of head-produced LhILPs, preventing the clearance of injected trehalose, a condition that could be rescued with co-injection of heterologous insulin. Stage-specific expression in LhILP RNAi insects suggest that LhILPs have multiple additional roles besides hemolymph carbohydrate homeostasis in L. hesperus that remain to be explored.