Cross-infectivity of honey and bumble bee-associated parasites across three bee families

Abstract

<jats:title>Abstract</jats:title> <jats:p>Recent declines of wild pollinators and infections in honey, bumble and other bee species have raised concerns about pathogen spillover from managed honey and bumble bees to other pollinators. Parasites of honey and bumble bees include trypanosomatids and microsporidia that often exhibit low host specificity, suggesting potential for spillover to co-occurring bees <jats:italic>via</jats:italic> shared floral resources. However, experimental tests of trypanosomatid and microsporidial cross-infectivity outside of managed honey and bumble bees are scarce. To characterize potential cross-infectivity of honey and bumble bee-associated parasites, we inoculated three trypanosomatids and one microsporidian into five potential hosts – including four managed species – from the apid, halictid and megachilid bee families. We found evidence of cross-infection by the trypanosomatids <jats:italic>Crithidia bombi</jats:italic> and <jats:italic>C. mellificae</jats:italic>, with evidence for replication in 3/5 and 3/4 host species, respectively. These include the first reports of experimental <jats:italic>C. bombi</jats:italic> infection in <jats:italic>Megachile rotundata</jats:italic> and <jats:italic>Osmia lignaria</jats:italic>, and <jats:italic>C. mellificae</jats:italic> infection in <jats:italic>O. lignaria</jats:italic> and <jats:italic>Halictus ligatus</jats:italic>. Although inability to control amounts inoculated in <jats:italic>O. lignaria</jats:italic> and <jats:italic>H. ligatus</jats:italic> hindered estimates of parasite replication, our findings suggest a broad host range in these trypanosomatids, and underscore the need to quantify disease-mediated threats of managed social bees to sympatric pollinators.</jats:p>

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

“…Crithidia spp. can infect bumblebees, honeybees and several solitary bee species 74 – 82 . The neogregarines are an understudied group, with one described bee parasite, Apicystis bombi .…”

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

“…While phylogenetic distance often predicts the ability of hosts to be infected by a given pathogen (Gilbert and Webb, 2007; Streicker et al ., 2010), this may not be the case with C. bombi and its known hosts. Specifically, one recent study (Ngor et al ., 2020) has found that C. bombi does not replicate in honey bees ( Apis mellifera ), but this pathogen does replicate in bumble bees ( Bombus spp.). Both honey bees and bumble bees are in the Apidae family, while the two evaluated solitary bees evaluated in the present study are in the Megachilidae family.…”

“…frequently harbour pollen in their digestive tract (Urban-Mead et al ., unpublished results). The importance of males in dispersing pathogens in plant–pollinator networks is not well established, despite male and female solitary bees having comparable infection rates (Müller et al ., 2019; Strobl et al ., 2019; Ngor et al ., 2020) and marked differences in floral preference (Roswell et al ., 2019). Moreover, natural rates of pathogen acquisition or deposition by solitary bees while foraging is not known (Figueroa et al ., 2019), including the threshold of pathogen cells necessary for solitary bees to develop active infections, all of which could strengthen disease spread models.…”

“…The solitary bees Osmia lignaria and M. rotundata are cavity-nesting species that provide important pollination services for fruits and vegetables in North America and Europe (Velthuis and van Doorn, 2006; Pitts-Singer and Cane, 2011; Brittain et al ., 2013) and can serve as model organisms for experimentally evaluating epidemiological questions due to their commercial availability. Recent experimental work has shown that C. bombi collected from B. impatiens can infect these species (Ngor et al ., 2020), further highlighting the need to understand the biotic and abiotic factors, such as diet, that influence disease dynamics in species beyond honey bees and bumble bees.…”

Pathways for Novel Epidemiology: Plant–Pollinator–Pathogen Networks and Global Change

“…While pathogen research in pollinators is heavily biased towards honey bees and bumble bees, recent studies point to broader pathogen host ranges, such as Crithidia bombi infections in multiple bee families [30]. Pathogen strains or taxa can behave as specialists or generalists in terms of host range, virulence, and infectivity, affecting their fitness and ability to cross species boundaries [28].…”