Sunflower pollen reduces a gut pathogen in worker and queen but not male bumble bees

Abstract

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 pathogen Crithidia bombi in 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 commercial B. 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 reduced Crithidia infection 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. Reducing Crithidia infection 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.

Sunflower pollen reduces a gut pathogen in the model bee species, Bombus impatiens , but has weaker effects in three wild congeners

“…Sunflower pollen strongly reduced Crithidia infection in wild and commercial B. impatiens (figures 1-4), consistent with previous findings [8,9,45,46], and had variable effects in the other bumblebee species we tested. In B. bimaculatus and B. vagans, sunflower pollen slightly reduced Crithidia infection intensity but not significantly so (figure 2), while it significantly reduced Crithidia prevalence in both species (figure 3), although further replication is required to verify this pattern in B. vagans since results are based on workers from one natal colony.…”

“…The low protein and high lipid content of sunflower pollen may be a poor resource for brood production, but it could provide benefits to the next generation. For example, free foraging commercial B. impatiens on farms with more sunflowers produced more daughter queens (Malfi RL et al, unpublished data) and sunflower pollen reduced Crithidia infections in B. impatiens queens [9]. Given that daughter queens emerge in late summer when sunflowers are blooming, feeding on sunflower pollen may increase queen likelihood of surviving diapause by reducing Crithidia infection [55] and providing a relatively high source of lipids, an essential nutrient for diapause [56], at the end of the summer.…”

“…Host diet can have important consequences for pathogen infection outcomes [7]. Consuming sunflower pollen (Helianthus annuus) dramatically reduced the gut pathogen, C. bombi, in commercial bumblebee (B. impatiens) workers [8] and queens [9]. Bumblebees in commercial colonies consume sunflower pollen when provided directly to the colony [10] and collect sunflower pollen when available in the landscape (R.L.…”

Novel data support model linking floral resources and honey bee competition with bumble bee abundances in coastal scrub

“…Reduced access to the aster E. staechadifolium potentially affects the amount, diversity, and nutritional characteristics of collected pollen, all associated with Bombus colony development and reproductive success (Thomson & Page 2020). Intriguing recent research suggests that aster pollen may benefit bumble bee health by altering microbiome composition and promoting parasite resistance (Giacomini et al 2018;LoCascio et al 2019;Fowler et al 2020). Nutritional status and pathogen load in newly emerged queens could affect overwinter survival and nest establishment success in the following spring (Woodard et al 2019).…”

Differential Bumble Bee Gene Expression Associated With Pathogen Infection And Pollen Diet

“…Consumption of sun ower (Helianthus annuus) pollen was recently discovered to reduce severity of the gut protozoan pathogen Crithidia bombi in Bombus impatiens worker and queen bumble bees by at least 80% relative to control pollen (12)(13)(14). The medicinal effect of sun ower pollen may extend beyond bumble bees and C. bombi.…”