Bacterial communities in Asecodes hispinarum (Hymenoptera: Eulophidae) and its host Brontispa longissima (Coleoptera: Chrysomelidae), with comparison of Wolbachia dominance.

The endoparasitoid Asecodes hispinarum (Boucek) (Hymenoptera: Eulophidae) serves as an effective biological control agent against Brontispa longissima (Gestro) (Coleoptera: Chrysomelidae), a notorious palm pest. Endosymbionts found in parasitoids and their hosts have attracted significant attention due to their substantial influence on biocontrol efficacy. In this study, we employed 16S rRNA sequencing, polymerase chain reaction, and fluorescence in situ hybridization to assess the symbiotic bacteria composition, diversity, phylogeny, and localization in A. hispinarum and its host B. longissima. Our findings showed significant differences in the richness, diversity, and composition of symbiotic bacteria among different life stages of B. longissima. Notably, the bacterial richness, diversity, and composition of A. hispinarum was similar to that of B. longissima. Firmicutes and Proteobacteria were the dominant phyla, while Wolbachia was the dominant genera across the parasitoid and host. It was discovered for the first time that Wolbachia was present in A. hispinarum with a high infection rate at ≥ 96.67%. Notably, the Wolbachia strain in A. hispinarum was placed in supergroup A, whereas it was categorized under supergroup B in B. longissima. Furthermore, Wolbachia is concentrated in the abdomen of A. hispinarum, with particularly high levels observed in the ovipositors of female adults. These findings highlight the composition and diversity of symbiotic bacteria in both A. hispinarum and its host B. longissima, providing a foundation for the development of population regulation strategies targeting B. longissima.

The Cellular Immunological Responses and Developmental Differences between Two Hosts Parasitized by Asecodes hispinarum.

This study aims to investigate the developmental interactions of Asecodes hispinarum Boucek on Brontispa longissima Gestro and Octodonta nipae Maulik, as well as the cellular immune responses of B. longissima and O. nipae larvae in response to parasitism by A. hispinarum, with the hope of determining the reason for the difference in larval breeding of A. hispinarum in B. longissima and O. nipae. The effects of parasitism by A. hispinarum on the larval development, hemocyte count, and proportion of the hemocyte composition of the two hosts were carried out through selective assay and non-selective assay using statistical analysis and anatomical imaging. There was no significant difference in parasitic selection for A. hispinarum on the larvae of these two beetles; however, more eggs were laid to B. longissima larvae than to O. nipae larvae after parasitism by A. hispinarum. The eggs of A. hispinarum were able to grow and develop normally inside the larvae of B. longissima, and the parasitism caused the larvae of B. longissima become rigid within 7 d, with a high larval mortality rate of 98.88%. In contrast, the eggs of A. hispinarum were not able to develop normally inside the O. nipae larvae, with a high encapsulation rate of 99.05%. In addition, the parasitism by A. hispinarum caused a 15.31% mortality rate in O. nipae larvae and prolonged the larval stage by 5 d and the pupal stage by 1 d. The number of hemocytes during the 12, 24, 48, 72, and 96 h of the four instars from O. nipae larvae was 6.08 times higher than from B. longissima larvae of the same age. After 24 h of being parasitized by A. hispinarum, the total number of hemocytes and granulocyte proportion of B. longissima larvae increased significantly. However, the total number of hemocytes and plasmatocyte proportion of O. nipae increased significantly after 24, 72, and 96 h, and the proportion of granulocytes increased significantly after 12 h post-parasitism. The results in the present study indicated that A. hispinarum was unable to successfully reproduce offspring in O. nipae, but its spawning behavior had an adverse effect on the larval development of its host. In addition, the adequate number of hemocytes and more pronounced changes in the hemocyte count and hemocyte composition ratio in the larvae after parasitization may be important factors for the successful encapsulation in O. nipae larvae.

Identification of putative odorant binding protein genes in Asecodes hispinarum, a parasitoid of coconut leaf beetle (Brontispa longissima) by antennal RNA-Seq analysis.

Asecodes hispinarum (Hymenoptera: Eulophidae) is an endoparasitoid and an efficient biological control agent which attacks larvae of Brontispa longissima, a serious insect pest of Palmae plants in China. Odorant binding proteins (OBPs) are believed to be important for transporting semiochemicals through the aqueous sensillar lymph to the olfactory receptor cells within the insect antennal sensilla. No previous study has reported on OBPs in A. hispinarum. In this study, we conducted the large-scale identification of OBP genes from the antennae of A. hispinarum by using transcriptome sequencing. Approximately 28.4 million total raw reads and about 27.3 million total clean reads were obtained, and then 46,363 unigenes were assembled. Of these unigenes, a total of 21,263 can be annotated in the NCBI non-redundant database. Among the annotated unigenes, 16,623 of them can be assigned to GO (Gene Ontology). Furthermore, we identified 8 putative OBP genes, and a phylogenetic tree analysis was performed to characterize the 8 OBP genes. In addition, the expression of the 8 OBP genes in different A. hispinarum body tissues was analyzed by real-time quantitative polymerase chain reaction (qRT-PCR). The results indicated that the 8 OBP genes were expressed accordingly to sexes and tissues, but all highly expressed in antennae. The finding of this study will lay the foundation for unraveling molecular mechanisms of A. hispinarum chemoperception.