Exposure of Larvae of the Solitary Bee Osmia bicornis to the Honey Bee Pathogen Nosema ceranae Affects Life History

Abstract

Wild bees are important pollinators of wild plants and agricultural crops and they are threatened by several environmental stressors including emerging pathogens. Honey bees have been suggested as a potential source of pathogen spillover. One prevalent pathogen that has recently emerged as a honey bee disease is the microsporidian Nosema ceranae. While the impacts of N. ceranae in honey bees are well documented, virtually nothing is known about its effects in solitary wild bees. The solitary mason bee Osmia bicornis is a common pollinator in orchards and amenable to commercial management. Here, we experimentally exposed larvae of O. bicornis to food contaminated with N. ceranae and document spore presence during larval development. We measured mortality, growth parameters, and timing of pupation in a semi-field experiment. Hatched individuals were assessed for physiological state including fat body mass, wing muscle mass, and body size. We recorded higher mortality in the viable-spore-exposed group but could only detect a low number of spores among the individuals of this treatment. Viable-spore-treated individuals with higher head capsule width had a delayed pupation start. No impact on the physiological status could be detected in hatched imagines. Although we did not find overt evidence of O. bicornis infection, our findings indicate that exposure of larvae to viable N. ceranae spores could affect bee development.

Dominant bee species and floral abundance drive parasite temporal dynamics in plant-pollinator communities

“…The effects of microsporidia infections in honeybees and bumblebees includes wing deformity, reduced foraging efficiency, reduced colony fitness and increased mortality, with N. bombi being found in multiple species of bumblebees and N. ceranae found in bumblebees and honeybees 65 – 71 In addition N. ceranae may be able to infect the mason bee, Osmia bicornis 72 . While this study did not find impacts on survival, a similar study that assessed impacts of N. ceranae on larval O. bicornis did find negative impacts on survival 73 . The trypanosomatids are mostly Crithidia species whose cells are transmitted via the fecal-oral route.…”

Susceptibility of Red Mason Bee Larvae to Bacterial Threats Due to Microbiome Exchange with Imported Pollen Provisions

“…Considering solitary bees, knowledge about their natural and healthy microbiomes advanced in the recent years [ 19 , 20 , 21 , 22 , 23 , 24 ]. Studies investigating potential microbial pathogens, however, focused on infections that are common between honey bees or bumble bees and solitary bees [ 25 , 26 , 27 ]. While studies investigated non-lethal endosymbionts in solitary bees, e.g., Wolbachia [ 28 ], dedicated studies screening for potential bacterial pathogens and other harmful bacteria in solitary bees specifically are currently lacking.…”

Crithidia bombican infect two solitary bee species while host survivorship depends on diet

“…Most bee species within a community can be exposed to numerous pathogens when foraging at flowers, including C. bombi (Figueroa et al ., 2020; Graystock et al ., 2020). Our results support a growing body of literature indicating the need to assess the host range of bee pathogens, including assessments of replication and impacts on survival (Bramke et al ., 2019; Müller et al ., 2019). The presence of C. bombi in bee feces has been used to identify active infections in bumble bees (Imhoof and Schmid-Hempel, 1999), where it can be detected in as quickly as 5 days post-inoculation (Logan et al ., 2005).…”

“…This includes pathogens known to infect honey bees and bumble bees (Apidae), including Apicystis bombi , Ascosphaera spp., C. bombi , C. mellificae , N. ceranae and numerous viruses (Singh et al ., 2010; Evison et al ., 2012; Ravoet et al ., 2014; Schoonvaere et al ., 2018; Figueroa et al ., 2020). However, except for single-stranded RNA viruses which allow for strand-specific PCR assays to detect viral replication, we currently cannot distinguish between transient passage through the bee gut and active infections, nor do we know if there are negative consequences for the host based solely on molecular screenings (Bramke et al ., 2019). Some existing studies that have experimentally evaluated the impacts on solitary bee health have shown increased mortality associated with infections [e.g.…”

“…Some existing studies that have experimentally evaluated the impacts on solitary bee health have shown increased mortality associated with infections [e.g. Megachile rotundata larvae infected with the fungus Ascosphera aggregata (James, 2005) and Osmia bicornis infected with the neogregarine A. bombi and the microsporidian N. ceranae (Tian et al ., 2018; Bramke et al ., 2019)], further highlighting the need to address the host range of bee pathogens and negative consequences for these understudied bee species.…”