Characteristics of the Insulin-like Peptide Genes and Their Roles in the Ovarian Development of Zeugodacus cucurbitae (Coquillett)

The melon fly <i>Zeugodacus cucurbitae</i> (Coquillett) is a globally invasive pest responsible for substantial economic losses in the fruit and vegetable industries. Insulin-like peptides (ILPs) are evolutionarily conserved neuropeptides that play a crucial role in insect reproduction. In this study, six <i>ZcILPs</i> from the melon fly, designated as <i>ZcILP1</i>-<i>6</i>, were cloned. Phylogenetic analysis demonstrated a strong orthologous link with Dipteran ILPs. Spatiotemporal expression profiling revealed that <i>ZcILP1</i> and <i>ZcILP3</i> exhibit preferential enrichment in the adult female fat body, with their expression specifically and significantly upregulated in 5-day-old individuals. Their expression decreased 12, 24, and 48 h post-starvation and increased upon re-feeding. Silencing <i>ZcILP1</i> and <i>ZcILP3</i> resulted in reduced ovarian size by 51.42% and 69.17%, respectively. Furthermore, silencing <i>ZcILP1</i> or <i>ZcILP3</i> significantly decreased the transcriptional levels of genes downstream of the insulin signaling pathway (ISP), notably the <i>target of rapamycin</i> (<i>ZcTOR</i>) and <i>Forkhead box O</i> (<i>ZcFOXO</i>). Concurrently, the expression of <i>Vitellogenin</i> (<i>ZcVg</i>), a gene associated with reproduction, was significantly downregulated. These findings indicate that <i>ZcILP1</i> and <i>ZcILP3</i> regulate <i>ZcVgs</i> expression and ovarian development through ISP, suggesting them as potential targets for green control of <i>Z. cucurbitae</i>.