Laterally acquired chitinase genes in venom facilitate parasitism in egg parasitoid wasps

Parasitoid wasps (Hymenoptera) play a crucial role in ecosystems and agroforestry pest management as biological control agents. These wasps utilize venom proteins to suppress host immunity and regulate physiology, facilitating offspring development. Although venom functions have been studied in some parasitoids, their roles in egg parasitoids remain poorly understood. In this study, we employed genomic and transcriptomic sequencing to identify venom proteins in Anastatus japonicus and Anastatus fulloi, two egg parasitoids used in biological control. We discovered a significant expansion of GH19 chitinase in their genomes, with phylogenetic analysis indicating acquisition via lateral gene transfer (LGT) from microsporidian. Functional characterization revealed that four highly expressed GH19 chitinases, Aj13071/Aj13072 in A. japonicus and Af23628/Af23629 in A. fulloi are essential for host egg penetration; silencing these genes increased penetration time and resulted in smaller or incomplete holes. Additionally, silencing Aj13071 and Aj13072 in A. japonicus impaired female fecundity, while Af23628 and Af23629 in A. fulloi affected venom reservoir development and egg load, respectively. These findings underscore the critical roles of GH19 chitinases in host penetration and reproduction, offering new insights into the molecular mechanisms driving parasitism in egg parasitoids. This study advances our understanding of venom evolution and supports the development of targeted biological control strategies.