The dynamics of viruses are critical to our understanding of disease pathogenesis. Using honey bee Deformed wing virus (DWV) as a model, we conducted field and laboratory studies to investigate the roles of abiotic and biotic stress factors as well as host health conditions in dynamics of virus replication in honey bees. The results showed that temperature decline could lead to not only significant decrease in the rate for pupae to emerge as adult bees, but also an increased severity of the virus infection in emerged bees, partly explaining the high levels of winter losses of managed honey bees, Apis mellifera, around the world. By experimentally exposing adult bees with variable levels of parasitic mite Varroa destructor, we showed that the severity of DWV infection was positively correlated with the density and time period of Varroa mite infestation, confirming the role of Varroa mites in virus transmission and activation in honey bees. Further, we showed that host conditions have a significant impact on the outcome of DWV infection as bees that originate from strong colonies resist DWV infection and replication significantly better than bee originating from weak colonies. The information obtained from this study has important implications for enhancing our understanding of host‑pathogen interactions and can be used to develop effective disease control strategies for honey bees.

Pathogens and parasites represent significant threats to the health and well-being of honeybee species that are key pollinators of agricultural crops and flowers worldwide. We conducted a nationwide survey to determine the occurrence and prevalence of pathogens and parasites in Asian honeybees, Apis cerana, in China. Our study provides evidence of infections of A. cerana by pathogenic Deformed wing virus (DWV), Black queen cell virus (BQCV), Nosema ceranae, and C. bombi species that have been linked to population declines of European honeybees, A. mellifera, and bumble bees. However, the prevalence of DWV, a virus that causes widespread infection in A. mellifera, was low, arguably a result of the greater ability of A. cerana to resist the ectoprasitic mite Varroa destructor, an efficient vector of DWV. Analyses of microbial communities from the A. cerana digestive tract showed that Nosema infection could have detrimental effects on the gut microbiota. Workers infected by N. ceranae tended to have lower bacterial quantities, with these differences being significant for the Bifidobacterium and Pasteurellaceae bacteria groups. The results of this nationwide screen show that parasites and pathogens that have caused serious problems in European honeybees can be found in native honeybee species kept in Asia. Environmental changes due to new agricultural practices and globalization may facilitate the spread of pathogens into new geographic areas. The foraging behavior of pollinators that are in close geographic proximity likely have played an important role in spreading of parasites and pathogens over to new hosts. Phylogenetic analyses provide insights into the movement and population structure of these parasites, suggesting a bidirectional flow of parasites among pollinators. The presence of these parasites and pathogens may have considerable implications for an observed population decline of Asian honeybees.

Bumble bees are important pollinators in natural and agricultural ecosystems. Their social colonies are founded by individual queens, which, as the predominant reproductive females of colonies, contribute to colony function through worker production and fitness through male and new queen production. Therefore, queen health is paramount, but even though there has been an increasing emphasis on the role of gut microbiota for animal health, there is limited information on the gut microbial dynamics of bumble bee queens. Employing 16S rRNA amplicon sequencing and quantitative PCR, we investigate how the adult life stage and physiological state influence a queen’s gut bacterial community diversity and composition in unmated, mated, and ovipositing queens of Bombus lantschouensis. We found significant shifts in total gut microbe abundance and microbiota composition across queen states. There are specific compositional signatures associated with different stages, with unmated and ovipositing queens showing the greatest similarity in composition and mated queens being distinct. The bacterial genera Gilliamella, Snodgrassella, and Lactobacillus were relatively dominant in unmated and ovipositing queens, with Bifidobacterium dominant in ovipositing queens only. Bacillus, Lactococcus, and Pseudomonas increased following queen mating. Intriguingly, however, further analysis of unmated queens matching the mated queens in age showed that changes are independent of the act of mating. Our study is the first to explore the gut microbiome of bumble bee queens across key life stages from adult eclosion to egg laying and provides useful information for future studies of the function of gut bacteria in queen development and colony performance. IMPORTANCE Bumble bee queens undergo a number of biological changes as they transition through adult emergence, mating, overwintering, foraging, and colony initiation including egg laying. Therefore, they represent an important system to understand the link between physiological, behavioral, and environmental changes and host-associated microbiota. It is plausible that the bumble bee queen gut bacteria play a role in shaping the ability of the queen to survive environmental extremes and reproduce, due to long-established coevolutionary relationships between the host and microbiome members.