Introduction of Non-Native Pollinators Can Lead to Trans-Continental Movement of Bee-Associated Fungi

Abstract

Bees are essential pollinators for many flowering plants, including agriculturally important crops such as apple. As geographic ranges of bees or their host plants change as a result of human activities, we need to identify pathogens that could be transmitted among newly sympatric species to evaluate and anticipate their effects on bee communities. We used PCR screening and DNA sequencing to evaluate exposure to potentially disease-causing microorganisms in a pollinator of apple, the horned mason bee (Osmia cornifrons). We did not detect microsporidia, Wolbachia, or trypanosomes, which are common pathogens of bees, in any of the hundreds of mason bees screened. We did detect both pathogenic and apathogenic (saprophytic) fungal species in the genus Ascosphaera (chalkbrood), an unidentified species of Aspergillus fungus, and a strain of bacteria in the genus Paenibacillus that is probably apathogenic. We detected pathogenic fungal strains in asymptomatic adult bees that therefore may be carriers of disease. We demonstrate that fungi from the genus Ascosphaera have been transported to North America along with the bee from its native range in Japan, and that O. cornifrons is exposed to fungi previously only identified from nests of other related bee species. Further study will be required to quantify pathogenicity and health effects of these different microbial species on O. cornifrons and on closely-related native North American mason bees that may now be exposed to novel pathogens. A global perspective is required for pathogen research as geographic ranges of insects and microorganisms shift due to intentional or accidental introductions.

Floral and Foliar Source Affect the Bee Nest Microbial Community

“…Apart from plant pathogens, we also found the causative agent of chalkbrood disease in M. rotundata-the fungi Ascosphaera aggregata-present in pollen provisions. This disease is thought to be transmitted to larvae from the mother from either her natal nest or the environment [24], although we are unable to discern transmission mode from our data. Other potential bee fungal pathogens like Aspergillus niger were also found, indicating that bee larvae may be exposed in their nests.…”

“…Shared floral resources can serve as reservoirs of pathogen transmission between diseased and naïve bees [22]. As M. rotundata provides nourishment for its brood in the form of pollen provisions that it makes from floral resources, disease agents such as Ascosphaera (the fungi that causes chalkbrood [3]) and Aspergillus (the fungi that causes stonebrood [23]) can be obtained from floral surfaces and transmitted to the larvae via the pollen provision [24][25][26]. Notably, aside from insect disease, bees incidentally vector plant pathogenic fungi [27] and viruses [28] through visiting infected flowers and dispersing the disease through normal pollination behavior [29].…”

Viral transmission in honey bees and native bees, supported by a global black queen cell virus phylogeny

“…Some bee viruses can infect and replicate within Ascosphaera apis, which causes chalkbrood in honey bees (Li et al, 2014) and is known to be pathogenic in bumble bees (Maxfield-Taylor et al, 2015). Both pathogenic and saprotrophic strains have been found in solitary bees (Osmia cornifrons) (Hedtke et al, 2015).…”

First records of Hylaeus (Paraprosopis) pictipes Nylander, 1852 (Hymenoptera: Colletidae) in North America

“…Competition for floral resources and nesting sites creates potential for negative impact on native species (Goulson 2003). Introduction of pests and pathogens with exotic species is of concern (Hedtke et al 2015;Cameron et al 2016), but there are no studies of pathogens in introduced Hylaeus species. Should they occur, closely related species are most likely to be susceptible to introduced pathogens.…”