Molecular Basis for Stage-Specific Host Preference in the Aphid Parasitoid Binodoxys communis

The cotton aphid <i>Aphis gossypii</i> is a globally significant agricultural pest that threatens crop production through its prolific reproduction. While the parasitoid wasp <i>Binodoxys communis</i> offers promising potential for biological control, the molecular mechanisms underlying its reproductive manipulation of aphid hosts remain poorly understood. Here, we investigated the stage-specific parasitism strategies of <i>B. communis</i> on <i>A. gossypii</i> using integrated biological observations and transcriptomic analysis. Parasitism significantly prolonged aphid development and suppressed reproduction across all host stages, with severity inversely correlated with host age at parasitism. Transcriptomic analysis of ovaries of parasitized aphids revealed 1168 differentially expressed genes, with temporal progression from minimal changes in nymphs (7 DEGs at day 1) to extensive disruption in adults (549 DEGs at day 3). Notably, juvenile hormone acid methyltransferase (<i>JHAMT</i>), the rate-limiting enzyme in juvenile hormone biosynthesis, emerged as a master regulator that is differentially targeted across host stages. In 3rd instar nymphs, single-gene suppression of <i>JHAMT</i> (-3.23-fold change) achieved effective reproductive control, whereas adult parasitism required progressive manipulation of multiple genes including <i>JHAMT</i>, <i>FOHSDR</i>, <i>ALDH</i>, and <i>JHEH</i>. The vitellogenin-vitellogenin receptor system only showed coordinated downregulation in adults, whereas nymphs exhibited preemptive receptor suppression before vitellogenesis onset. These findings demonstrate that <i>B. communis</i> has evolved to exploit a developmental window where host manipulation is most efficient-3rd instar nymphs, which possess sufficient resources for parasitoid development and lack the complex compensatory mechanisms found in adults. This "low-cost, high-reward" strategy based on precision targeting of master regulators in nymphs compared to multi-gene assault in adults, revealing the evolutionary optimization of parasitoid manipulation strategies. Our results provide molecular insights into parasitoid-host coevolution and identified key regulatory targets for developing innovative biological control strategies against this important agricultural pest.