Oviposition Traits and Vitellogenin-Related Gene Functions in Ooencyrtus kuvanae

Ooencyrtus kuvanae is an egg parasitoid species that attacks the egg masses of Dendrolimus spp and Lymantria spp. in China, which gives it a temporal niche advantage against pest infestations by Dendrolimus spp. and Lymantria spp. Moreover, it has a short life cycle, high offspring outcome, and female-biased population, showing distinctive ovarian development and oviposition behaviors and thus providing an ideal model for reproductivity and regulatory mechanisms. Previous studies have found that the Vitellogenin (Vg) and Vitellogenin Receptor (VgR) genes play important regulatory roles in the ovarian development of a few wasp species, but little is known about how these two genes work within O. kuvanae. Therefore, we observed their oviposition traits, characterized their gene structure, and clarified the function of Vg and VgR. The results showed that continuous daily oviposition significantly reduced the daily mature eggs and offspring per female by providing a single host egg for oviposition in each experimental trial, while the proportion of female offspring reached 100%, indicating that thelytokous parthenogenesis occurred. The full-length sequences of OkVg and OkVgR were cloned and submitted to GenBank. qPCR detection revealed that the transcription levels were the highest in adults. Feeding 20-hydroxyecdysone can increase OkVg gene expression (by 2.4-fold), while feeding juvenile hormone can promote their OkVgR expression (by 2.3-fold). RNA interference significantly downregulated OkVg and OkVgR expression in adult ovaries. And dsVg significantly reduced the ovarian egg load by 45% (p < 0.05), while dsVgR caused oviduct contraction and offspring decrease. Simultaneous silencing of OkVg and OkVgR significantly reduced offspring outcomes, indicating both genes may jointly dominate oocyte development. This study provides functional evidence of molecular regulation and interaction between OkVg and its receptor genes.