New insights into fungal diversity associated with Megaplatypus mutatus: gut mycobiota

How host species and body part determine the microbial communities of five ambrosia beetle species

The ambrosia beetles are farming insects that feed mainly on their cultivated fungi, which in some occasions are pathogens from forest and fruit trees. We used a culture-independent approach based on 16S and 18S rRNA gene metabarcoding analysis to investigate the diversity and composition of the bacterial and fungal communities associated with five ambrosia beetle species: four species native to America (Monarthrum dimidiatum, Dryocoetoides capucinus, Euwallacea discretus, Corthylus consimilis) and an introduced species (Xylosandrus morigerus). For the bacterial community, the beetle species hosted a broad diversity with 1,579 amplicon sequence variants (ASVs) and 66 genera, while for the fungal community they hosted 288 ASVs and 39 genera. Some microbial groups dominated the community within a host species or a body part (Wolbachia in the head-thorax of E. discretus; Ambrosiella in the head-thorax and abdomen of X. morigerus). The taxonomic composition and structure of the microbial communities appeared to differ between beetle species; this was supported by beta-diversity analysis, which indicated that bacterial and fungal communities were clustered mainly by host species. This study characterizes for the first time the microbial communities associated with unexplored ambrosia beetle species, as well as the factors that affect the composition and taxonomic diversity per se, contributing to the knowledge of the ambrosia beetle system.

Cladosporium-Insect Relationships

The range of interactions between Cladosporium, a ubiquitous fungal genus, and insects, a class including about 60% of the animal species, is extremely diverse. The broad case history of antagonism and mutualism connecting Cladosporium and insects is reviewed in this paper based on the examination of the available literature. Certain strains establish direct interactions with pests or beneficial insects or indirectly influence them through their endophytic development in plants. Entomopathogenicity is often connected to the production of toxic secondary metabolites, although there is a case where these compounds have been reported to favor pollinator attraction, suggesting an important role in angiosperm reproduction. Other relationships include mycophagy, which, on the other hand, may reflect an ecological advantage for these extremely adaptable fungi using insects as carriers for spreading in the environment. Several Cladosporium species colonize insect structures, such as galleries of ambrosia beetles, leaf rolls of attelabid weevils and galls formed by cecidomyid midges, playing a still uncertain symbiotic role. Finally, the occurrence of Cladosporium in the gut of several insect species has intriguing implications for pest management, also considering that some strains have proven to be able to degrade insecticides. These interactions especially deserve further investigation to understand the impact of these fungi on pest control measures and strategies to preserve beneficial insects.

Mycobiomes of two distinct clades of ambrosia gall midges (Diptera: Cecidomyiidae) are species-specific in larvae but similar in nutritive mycelia

IMPORTANCE

Ambrosia gall midges are endophagous insect herbivores whose larvae live enclosed within a single gall for their entire development period. They may exhibit phytomycetophagy, a remarkable feeding mode that involves the consumption of plant biomass and mycelia of their cultivated gall symbionts. Thus, AGMs are ideal model organisms for studying the role of microorganisms in the evolution of host specificity in insects. However, compared to other fungus-farming insects, insect-fungus mutualism in AGMs has been neglected. Our study is the first to use DNA metabarcoding to characterize the complete mycobiome of the entire system of the gall-forming insects as we profiled gall surfaces, nutritive mycelia, and larvae. Interestingly, larval mycobiomes were significantly different from their nutritive mycelia, although Botryosphaeria dothidea dominated the nutritive mycelia, regardless of the evolutionary separation of the tribes studied. Therefore, we confirmed a long-time hypothesized paradigm for the important evolutionary association of this fungus with AGMs.

Profiling Analysis of Filter Feeder Polypedilum (Chironomidae) Gut Contents Using eDNA Metabarcoding Following Contrasting Habitat Types-Weir and Stream

We analyzed the dietary composition of Polypedilum larvae among two contrasting habitats (river and weir). Our approach was (i) to apply eDNA-based sampling to reveal the gut content of the chironomid larvae, (ii) the diversity of gut contents in the two aquatic habitats, and (iii) assessment of habitat sediment condition with the food sources in the gut. The most abundant food was Chlorophyta in the gut of the river (20%) and weir (39%) chironomids. The average ratio of fungi, protozoa, and zooplankton in river chironomids gut was 5.9%, 7.2%, and 3.8%, while it was found decreased to 1.2%, 2.5%, and 0.1% in weir chironomids. Aerobic fungi in river midge guts were 3.6% and 10.34% in SC and IS, while they were in the range of 0.34-2.58% in weir midges. The hierarchical clustering analysis showed a relationship of environmental factors with food contents. Abiotic factors (e.g., pH) in the river and weir habitats correlated the clustered pattern with phytoplankton and minor groups of fungi. This study could help understand the food source diversity in the chironomid and habitat environmental conditions by using eDNA metabarcoding as an effective tool to determine dietary composition.