The complete genome of Chelonus insularis reveals dynamic arrangement of genome components in parasitoid wasps that produce bracoviruses

Bracoviruses (BVs) are endogenized nudiviruses in parasitoid wasps of the microgastroid complex (family Braconidae). Microgastroid wasps have coopted nudivirus genes to produce replication-defective virions that females use to transfer virulence genes to parasitized hosts. The microgastroid complex further consists of six subfamilies and ∼50,000 species but current understanding of BV gene inventories and organization primarily derives from analysis of two wasp species in the subfamily Microgastrinae ( Microplitis demolitor and Cotesia congregata ) that produce M. demolitor BV (MdBV) and C. congregata BV (CcBV). Notably, several genomic features of MdBV and CcBV remain conserved since divergence of M. demolitor and C. congregata ∼53 million years ago (MYA). However, it is unknown whether these conserved traits more broadly reflect BV evolution, because no complete genomes exist for any microgastroid wasps outside of the Microgastrinae. In this regard, the subfamily Cheloninae is of greatest interest because it diverged earliest from the Microgastrinae (∼85 MYA) after endogenization of the nudivirus ancestor. Here, we present the complete genome of Chelonus insularis , which is an egg-larval parasitoid in the Cheloninae that produces C. insularis BV (CinsBV). We report that the inventory of nudivirus genes in C. insularis is conserved but are dissimilarly organized when compared to M. demolitor and C. congregata . Reciprocally, CinsBV proviral segments share organizational features with MdBV and CcBV but virulence gene inventories exhibit almost no overlap. Altogether, our results point to the functional importance of a conserved inventory of nudivirus genes and a dynamic set of virulence genes for the successful parasitism of hosts. Our results also suggest organizational features previously identified in MdBV and CcBV are likely not essential for BV virion formation. Significance Bracoviruses are a remarkable example of virus endogenization, because large sets of genes from a nudivirus ancestor continue to produce virions that thousands of wasp species rely upon to parasitize hosts. Understanding how these genes interact and have been coopted by wasps for novel functions is of broad interest in the study of virus evolution. This manuscript characterizes bracovirus genome components in the parasitoid wasp Chelonus insularis , which together with existing wasp genomes captures a large portion of the diversity among wasp species that produce bracoviruses. Results provide new information about how bracovirus genome components are organized in different wasps while also providing additional insights on key features required for function.

Egg Parasitoids Survey of Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) in Maize and Sorghum in Central Mexico

Spodoptera frugiperda (Smith) is the main maize pest in America and was recently detected as an invasive pest in some countries in Asia and Africa. Among its natural enemies presented in Mexico, Trichogramma pretiosum Riley is the only egg parasitoid used in Integrated Pest Management (IPM) programs regardless of its effectiveness. A search for natural enemies of S. frugiperda was then carried out to determine whether this parasitoid has been established, and to detect native egg parasitoids or predators associated with this pest. The sentinel technique (egg masses) was used, and then placed in maize and sorghum fields in the state of Guanajuato, Mexico. Trichogramma atopovirilia Oatman and Platner, an egg parasitoid, and Chelonus insularis Cresson egg-larva parasitoid were recovered from field surveys. Among the natural enemies that preyed on eggs of S. frugiperda, we found mites of the genus Balaustium, and Dermaptera of the genus Doru, both species in great abundance. Laboratory tests were performed to compare the potential parasitism of T. atopovirilia against T. pretiosum. T. atopovirilia obtained 70.14% parasitism while T. pretiosum, 29.23%. In field cages, three doses of the parasitoids were tested. Total parasitism did not exceed 8% in any of the two species, but T. atopovirilia parasitized a greater number of hosts using two and three parasitoids per pest egg. Then, the use of Trichogramma species needs to be reevaluated in biological control programs against S. frugiperda.