Nanomaterial-mediated RNAi reveals the effect of the oral secretory protein serine protease inhibitor on the growth of Conogethes punctiferalis larvae.

The oral secretions of herbivorous insects play a pivotal role in insect-plant interactions and the regulation of insect physiology. Unlike the saliva of Hemiptera species, Lepidopteran oral secretions include both saliva and regurgitated gut fluids; yet research on their composition remains limited. This study focuses on yellow peach moth (YPM), Conogethes punctiferalis, a pest increasingly damaging maize. A total of 103 proteins were identified from oral secretions collected from larvae reared on corn and artificial diets, comprising 67 enzymes, 30 non-enzymes, and 6 unknowns. The identified enzyme proteins were primarily trypsin, lipase, and serine protease inhibitors (serpins). Further genomic investigation revealed 36 serpin genes in the YPM genome, distributed in clusters across various chromosomes, with some genes exhibiting partial synteny to homologous sequences in Ostrinia furnacalis. Among the identified serpin genes, the SpI gene (jg17839), which encoded the most abundant protein in YPM oral secretions, was found to exhibit peak expression in fifth-instar larvae and culticle tissues. Silencing of the SpI gene through nanomaterial-mediated RNA interference significantly reduced larval length, weight, pupation rates, and pupal weight, while also increased larval mortality. Moreover, interfering with SpI expression elevated juvenile hormone levels in the larvae. These findings indicate that the abundant SpI protein in YPM oral secretions plays a vital role in larval growth and development by modulating internal hormone levels. This study enriches the database of lepidopteran oral secretion components, fostering a deeper understanding of their physiological roles and informing eco-friendly pest control strategies targeting these proteins in YPM.