Bacterial and fungal midgut community dynamics and transfer between mother and brood in the Aisan longhorned beetle (Anoplophora glabipennis), an invasive xylophage

Authors: MASON, CHARLES - Pennsylvania State University; CAMPBELL, ALEXANDER - Pennsylvania State University; Scully, Erin; HOOVER, KELLI - Pennsylvania State University

Submitted to: Microbial Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2018
Publication Date: 1/15/2019
Citation: Mason, C.J., Campbell, A.M., Scully, E.D., Hoover, K. 2019. Bacterial and fungal midgut community dynamics and transfer between mother and brood in the Aisan longhorned beetle (Anoplophora glabipennis), an invasive xylophage. Microbial Ecology. 77(1):230-242. https://doi.org/10.1007/s00248-018-1205-1.
DOI: https://doi.org/10.1007/s00248-018-1205-1

Interpretive Summary: Many insects that feed in woody plant tissues harbor bacterial or fungal insects in their guts that help them break down plant cell walls and provide nutrients missing from plant tissue. The gut of the invasive, wood-boring Asian longhorned beetle (Anoplophora glabripennis) is colonized by bacteria and fungi that are hypothesized to fill these roles, including one fungal associate belonging to the Fusarium solani species complex (FSSC) that is consistently found in the gut. Despite the importance of these microbes to digestion and physiology, it is not clear which microbes are transmitted vertically from mother to offspring. In this study, we demonstrated that FSSC is transmitted from mother to offspring via excrement (frass) that is deposited onto the surface of the egg during the egg-laying process. In addition, several bacteria were also transmitted to offspring in this manner. These fungi and bacteria were likely consumed by the offspring and ultimately colonized their guts. Microbes transmitted from one generation to the next are often beneficial and have key roles in insect physiology; thus, the vertically transmitted microbes identified in Asian longhorned beetles could be targeted to control this insect.

Technical Abstract: Microbial symbionts play pivotal roles in the ecology and physiology of insects feeding in woody plants. Both eukaryotic and bacterial members occur in these systems where they facilitate digestive and nutrition provisioning. The larval gut of the Asian longhorned beetle (Anoplophora glabripennis) is associated with a microbial consortium that fulfills these metabolic roles. While members of the community vary in presence and abundance, A. glabripennis is consistently associated with a fungus in the Fusarium solani species complex (FSSC). We used amplicon sequencing, taxon-specific PCR, culturing, and imaging to determine how bacterial and fungal communities and populations differ between life stages and possible modes of symbiont transfer. The bacterial and fungal communities of adult guts were more diverse than those from larvae and eggs. The communities of larvae and eggs were more similar to those associated with the oviposition sites than to the adult female guts. FSSC was not detected in the reproductive tissues of adult females, but was consistently detected on egg surfaces after oviposition and in frass. These results demonstrate that frass can serve as a vehicle of vertical transmission of a subset of the microbiota. Vertically transmitted symbionts are often beneficial to their host, warranting subsequent functional studies.