skip to main content


Title: Crithidia bombi can infect two solitary bee species while host survivorship depends on diet
Abstract Pathogens and lack of floral resources interactively impair global pollinator health. However, epidemiological and nutritional studies aimed at understanding bee declines have historically focused on social species, with limited evaluations of solitary bees. Here, we asked whether Crithidia bombi , a trypanosomatid gut pathogen known to infect bumble bees, could infect the solitary bees Osmia lignaria (females) and Megachile rotundata (males), and whether nutritional stress influenced infection patterns and bee survival. We found that C. bombi was able to infect both solitary bee species, with 59% of O. lignaria and 29% of M. rotundata bees experiencing pathogen replication 5–11 days following inoculation. Moreover, access to pollen resulted in O. lignaria living longer, although it did not influence M. rotundata survival. Access to pollen did not affect infection probability or resulting pathogen load in either species. Similarly, inoculating with the pathogen did not drive survival patterns in either species during the 5–11-day laboratory assays. Our results demonstrate that solitary bees can be hosts of a known bumble bee pathogen, and that access to pollen is an important contributing factor for bee survival, thus expanding our understanding of factors contributing to solitary bee health.  more » « less
Award ID(s):
2010615
NSF-PAR ID:
10249567
Author(s) / Creator(s):
; ;
Date Published:
Journal Name:
Parasitology
Volume:
148
Issue:
4
ISSN:
0031-1820
Page Range / eLocation ID:
435 to 442
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Flowers can be transmission platforms for parasites that impact bee health, yet bees share floral resources with other pollinator taxa, such as flies, that may be hosts or non-host vectors (i.e., mechanical vectors) of parasites. Here, we assessed whether the fecal-orally transmitted gut parasite of bees,Crithidia bombi, can infectEristalis tenaxflower flies. We also investigated the potential for two confirmed solitary bee hosts ofC. bombi,Osmia lignariaandMegachile rotundata, as well as two flower fly species,Eristalis arbustorumandE. tenax,to transmit the parasite at flowers. We found thatC. bombidid not replicate (i.e., cause an active infection) inE. tenaxflies. However, 93% of inoculated flies defecated liveC. bombiin their first fecal event, and all contaminated fecal events containedC. bombiat concentrations sufficient to infect bumble bees. Flies and bees defecated inside the corolla (flower) more frequently than other plant locations, and flies defecated at volumes comparable to or greater than bees. Our results demonstrate thatEristalisflower flies are not hosts ofC. bombi, but they may be mechanical vectors of this parasite at flowers. Thus, flower flies may amplify or diluteC. bombiin bee communities, though current theoretical work suggests that unless present in large populations, the effects of mechanical vectors will be smaller than hosts.

     
    more » « less
  2. Abstract

    Pathogen transmission between domesticated and wild host species has important implications for community ecology, agriculture, and wildlife conservation. Bumble bees provide valuable pollination services that are vital for both wildflowers and agricultural production. Intense concerns about pathogen spillover from commercial bumble bees to wild bee populations, and the potential harmful effects of pathogen spillback to commercial bees, has stimulated a need for practical strategies that effectively manage bumble bee infectious diseases. Here, we assessed the costs and benefits of a medicinal sunflower pollen diet (Helianthusannuus) on whole‐colony bumble bee disease and performance using commercial colonies of the common eastern bumble bee,Bombus impatiens, and its protozoan pathogen,Crithidia bombi(Trypanosomatida). We first found that a 1:1 mixture of sunflower combined with wildflower pollen reducedC. bombiinfection prevalence and intensity within individualB. impatiensworkers by nearly 4‐fold and 12‐fold, respectively, relative to wildflower pollen. At the colony level, a 1:1 mixture of sunflower and wildflower pollen reducedC. bombiinfection prevalence by 11% averaged over a 10‐week period and infection intensity by 30% relative to wildflower pollen. Colony performance was similar between pollen diets and infection treatments, including the number of workers and immatures produced, and size and weight of workers, drones, and queens. Infection significantly reduced the probability of queen production in colonies fed a pure wildflower pollen diet, but not colonies fed a mixed sunflower pollen diet, suggesting that the medicinal benefits of a mixed sunflower pollen diet can reverse the negative effects of infection on reproductive success. This study provides evidence that sunflower pollen as part of a mixed pollen diet can reduce infection in individual bees and whole colonies with no significant nutritional trade‐offs for colony worker production and most aspects of colony reproduction. A supplemental mixed sunflower pollen diet may provide a simple and effective solution to reduce disease and improve the health of economically and ecologically important pollinators.

     
    more » « less
  3. Abstract

    Plants have unique chemical and physical traits that can reduce infections in animals ranging from primates to caterpillars. Sunflowers (Helianthus annuus; Asteraceae) are one striking example, with pollen that suppresses infections by the trypanosomatid gut pathogenCrithidia bombiin the common eastern bumble bee (Bombus impatiens). However, the mechanism underlying this effect has remained elusive, and we do not know whether pollens from other Asteraceae species have similar effects.

    We evaluated whether mechanisms mediating sunflower pollen's antipathogenic effects are physical (due to its spiny exine), chemical (due to metabolites) or both. We also evaluated the degree to which pollen from seven other Asteraceae species reducedC. bombiinfection relative to pollen from sunflower and two non‐Asteraceae species, and whether pollen spine length predicted pathogen suppression.

    We found that sunflower exines alone reduced infection as effectively as whole sunflower pollen, while sunflower pollen metabolites did not. Furthermore, bees fed pollen from four of seven other Asteraceae had 62%–92% lowerC. bombiinfections than those fed non‐Asteraceae pollen. Spine length, however, did not explain variation in bumble bee infection.

    Our study indicates that sunflower pollen's capacity to suppressC. bombiis driven by its spiny exine, and that this phenomenon extends to several other Asteraceae species. Our results indicate that sunflower pollen exines are as effective as whole pollen in reducing infection, suggesting that future studies should expand to assess the effects of other species with spiny pollen on pollinator–pathogen dynamics.

    Read the freePlain Language Summaryfor this article on the Journal blog.

     
    more » « less
  4. Abstract

    Global declines in pollinators, including bees, can have major consequences for ecosystem services. Bees are dominant pollinators, making it imperative to mitigate declines. Pathogens are strongly implicated in the decline of native and honey bees. Diet affects bee immune responses, suggesting the potential for floral resources to provide natural resistance to pathogens. We discovered that sunflower (Helianthus annuus) pollen dramatically and consistently reduced a protozoan pathogen (Crithidia bombi) infection in bumble bees (Bombus impatiens) and also reduced a microsporidian pathogen (Nosema ceranae) of the European honey bee (Apis mellifera), indicating the potential for broad anti-parasitic effects. In a field survey, bumble bees from farms with more sunflower area had lowerCrithidiainfection rates. Given consistent effects of sunflower in reducing pathogens, planting sunflower in agroecosystems and native habitat may provide a simple solution to reduce disease and improve the health of economically and ecologically important pollinators.

     
    more » « less
  5. 1. Social insect castes and sexes differ in many ways, including morphology, behavior, and sometimes ploidy level. Recent studies have found that consuming sunflower pollen reduces the gut pathogenCrithidia bombiin workers of the common eastern bumble bee (Bombus impatiens). Here, this work is extended to the reproductive individuals that represent colony fitness – males and queens – to assess if the medicinal effects of sunflower pollen vary with bee caste and sex.

    2. This study examined the effect of sunflower pollen compared to a diverse wildflower pollen mix on infection in worker, male, and daughter queen commercialB.impatiens. Bees were infected, fed either sunflower pollen or wildflower pollen for 7 days, and then infection levels were assessed.

    3. Compared to wildflower pollen, sunflower pollen dramatically reducedCrithidiainfection in workers and daughter queens, but not males. Infection levels were very low for both diets in males; this could be due to low pollen consumption or other mechanisms.

    4. ReducingCrithidiainfection in young queens before they undergo hibernation is important for population dynamics since infected queens are less likely to survive hibernation, and those that do are less likely to successfully establish a nest the following spring. Because sunflowers bloom in late summer when new queens are emerging, sunflowers could provide an important dietary component for queens during this critical life stage. Deepening our understanding of how diet impacts pathogens in reproductive bees, as well as workers, is crucial to maintain healthy pollinator populations.

     
    more » « less