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Social bees have been extensively studied for their gut microbial functions, but the significance of the gut microbiota in solitary bees remains less explored. Solitary bee, Megachile rotundata females provision their offspring with pollen from various plant species, harboring a diverse microbial community that colonizes larvae guts. The Apilactobacillus is the most abundant microbe, but evidence concerning the effects of Apilactobacillus and other provision microbes on growth and survival are lacking. We hypothesized that the presence of Apilactobacillus in abundance would enhance larval and prepupal development, weight, and survival, while the absence of intact microbial communities was expected to have a negative impact on bee fitness. We reared larvae on pollen provisions with naturally collected microbial communities (Natural pollen) or devoid of microbial communities (Sterile pollen). We also assessed the impact of introducing Apilactobacillus micheneri by adding it to both types of pollen provisions. Feeding larvae with sterile pollen + A. micheneri led to the highest mortality rate, followed by natural pollen + A. micheneri , and sterile pollen. Larval development was significantly delayed in groups fed with sterile pollen. Interestingly, larval and prepupal weights did not significantly differ across treatments compared to natural pollen-fed larvae. 16S rRNA gene sequencing found a dominance of Sodalis , when A. micheneri was introduced to natural pollen. The presence of Sodalis with abundant A. michene ri suggests potential crosstalk between both, shaping bee nutrition and health. Hence, this study highlights that the reliance on nonhost-specific environmental bacteria may not impact fitness of M. rotundata .IMPORTANCEThis study investigates the impact of environmentally acquired gut microbes of solitary bee fitness with insights into the microbial ecology of bee and their health. While the symbiotic microbiome is well-studied in social bees, the role of environmental acquired microbiota in solitary bees remains unclear. Assessing this relationship in a solitary pollinator, the leaf-cutting bee, Megachile rotundata , we discovered that this bee species does not depend on the diverse environmental bacteria found in pollen for either its larval growth or survival. Surprisingly, high concentrations of the most abundant pollen bacteria , Apilactobacillus micheneri did not consistently benefit bee fitness, but caused larval mortality. Our findings also suggest an interaction between Apilactobacillus and the Sodalis and perhaps their role in bee nutrition. Hence, this study provides significant insights that contribute to understanding the fitness, conservation, and pollination ecology of other solitary bee species in the future., Competing Interests: The authors declare no conflict of interest.

Ascosphaera (Eurotiomycetes: Onygenales) is a diverse genus of fungi that is exclusively found in association with bee nests and comprises both saprophytic and entomopathogenic species. To date, most genomic analyses have been focused on the honeybee pathogen A. apis, and we lack a genomic understanding of how pathogenesis evolved more broadly in the genus. To address this gap we sequenced the genomes of the leaf-cutting bee pathogen A. aggregata as well as three commensal species: A. pollenicola, A. atra and A. acerosa. De novo annotation and comparison of the assembled genomes was carried out, including the previously published genome of A. apis. To identify candidate virulence genes in the pathogenic species, we performed secondary metabolite-oriented analyses and clustering of biosynthetic gene clusters (BGCs). Additionally, we captured single copy orthologs to infer their phylogeny and created codon-aware alignments to determine orthologs under selective pressure in our pathogenic species. Our results show several shared BGCs between A. apis, A. aggregata and A. pollenicola, with antifungal resistance related genes present in the bee pathogens and commensals. Genes involved in metabolism and protein processing exhibit signatures of enrichment and positive selection under a fitted branch-site model. Additional known virulence genes in A. pollenicola, A. acerosa and A. atra are identified, supporting previous hypotheses that these commensals may be opportunistic pathogens. Finally, we discuss the importance of such genes in other fungal pathogens, suggesting a common route to evolution of pathogenicity in Ascosphaera., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

The insect order Hemiptera, one of the best-studied insect lineages with respect to bacterial symbioses, still contains major branches that lack comprehensive characterization of associated bacterial symbionts. The Pyrrhocoroidea (Largidae [220 species] and Pyrrhocoridae [∼300 species]) is a clade of the hemipteran infraorder Pentatomomorpha. Studies on bacterial symbionts of this group have focused on members of Pyrrhocoridae, but recent examination of species of two genera of Largidae demonstrated divergent symbiotic complexes in these putative sister families. We surveyed the associated bacterial diversity of this group using paired-end Illumina sequencing and targeted Sanger sequencing of bacterial 16S rRNA amplicons of 30 pyrrhocoroid taxa, including 17 species of Largidae, in order to determine bacterial associates and the similarity of associated microbial communities among species. We also used molecular data (4,800 bp in 5 loci, for 57 ingroup and 12 outgroup taxa) to infer a phylogeny of the host superfamily, in order to trace the evolution of symbiotic complexes among Pentatomomorpha species. We undertook multiple lines of investigation (i.e., experimental rearing, fluorescence in situ hybridization microscopy, and phylogenetic and coevolutionary analyses) to elucidate potential transmission routes for largid symbionts. We found a prevalent and specific association of Largidae with Burkholderia strains of the plant-associated beneficial and environmental clade, housed in midgut tubules. As in other distantly related Heteroptera, symbiotic bacteria seem to be acquired from the environment every generation. We review the current understanding of symbiotic complexes within Pentatomomorpha and discuss means to further investigate the evolution and function of these symbioses., Importance: Obligate symbioses with bacteria are common in insects, particularly Hemiptera, in which various forms of symbiosis occur. However, knowledge regarding symbionts remains incomplete for major hemipteran lineages. Thus, an accurate understanding of how these partnerships evolved and changed over millions of years is not yet achievable. We contribute to our understanding of the evolution of symbiotic complexes in Hemiptera by characterizing bacterial associates of Pyrrhocoroidea, focusing on the family Largidae. Members of Largidae are associated with specific symbiotic Burkholderia strains from a different clade than Burkholderia symbionts in other Burkholderia-associated Hemiptera. Evidence suggests that species of Largidae reacquire specific symbiotic bacteria from the environment every generation, which is a rare strategy for insects, with potentially volatile evolutionary ramifications, but one that must have persisted in Largidae and related lineages since their origin in the Cretaceous Period., (Copyright © 2016, American Society for Microbiology. All Rights Reserved.)

As pollinators, bees are cornerstones for terrestrial ecosystem stability and key components in agricultural productivity. All animals, including bees, are associated with a diverse community of microbes, commonly referred to as the microbiome. The bee microbiome is likely to be a crucial factor affecting host health. However, with the exception of a few pathogens, the impacts of most members of the bee microbiome on host health are poorly understood. Further, the evolutionary and ecological forces that shape and change the microbiome are unclear. Here, we discuss recent progress in our understanding of the bee microbiome, and we present challenges associated with its investigation. We conclude that global coordination of research efforts is needed to fully understand the complex and highly dynamic nature of the interplay between the bee microbiome, its host, and the environment. High-throughput sequencing technologies are ideal for exploring complex biological systems, including host-microbe interactions. To maximize their value and to improve assessment of the factors affecting bee health, sequence data should be archived, curated, and analyzed in ways that promote the synthesis of different studies. To this end, the BeeBiome consortium aims to develop an online database which would provide reference sequences, archive metadata, and host analytical resources. The goal would be to support applied and fundamental research on bees and their associated microbes and to provide a collaborative framework for sharing primary data from different research programs, thus furthering our understanding of the bee microbiome and its impact on pollinator health., (Copyright © 2016 Engel et al.)

Sexual reproduction brings together and recombines different genomes. Associated with these contacts is transmission of microorganisms and selfish genetic elements, many of which can be harmful to the host. In organisms with internal fertilization, sexually transmitted infections are caused by pathogens transmitted between the parents participating in mating. Sexual transmission has different epidemiological dynamics from nonsexual transmission in that it is less likely to be dependent on host density, there may be no population density threshold for disease increase, and it is more likely to lead to host extinction. Analysis of the evolutionary pathways that have led to the sexual mode of transmission in pathogens indicates that sexual transmission appears more often to be derived from nonsexual transmission, although the pathways are highly variable, and several groups of pathogens are exceptions to this rule. Sexual transmission has evolved from a wide variety of alternative transmission modes, although rarely from aerially transmitted diseases. More data are needed on the phylogeny and transmission mode of the relatives of sexually transmitted pathogens in order to guide development of animal models and comparative studies., (© 2011 New York Academy of Sciences.)