Effects of planted pollinator habitat on pathogen prevalence and interspecific detection between bee species

Abstract

Shared resources can instigate pathogen spread due to large congregations of individuals in both natural and human modified resources. Of current concern is the addition of pollinator habitat in conservation efforts as it attracts bees of various species, potentially instigating interspecific sharing of pathogens. Common pathogens have been documented across a wide variety of pollinators with shared floral resources instigating their spread in some, but not all, cases. To evaluate the impact of augmented pollinator habitat on pathogen prevalence, we extracted RNA from samples of eight bee species across three families and screened these samples for nine pathogens using RT-qPCR. We found that some habitat characteristics influenced pathogen detection; however, we found no evidence that pathogen detection in one bee species was correlated with pathogen detection in another. In fact, pathogen detection was rare in wild bees. While gut parasites were detected in 6 out of the 8 species included in this study, viruses were only detected in honey bees. Further, virus detection in honey bees was low with a maximum 21% of samples testing positive for BQCV, for example. These findings suggest factors other than the habitat itself may be more critical in the dissemination of pathogens among bee species. However, we found high relative prevalence and copy number of gut parasites in some bee species which may be of concern, such as Bombus pensylvanicus. Long-term monitoring of pathogens in different bee species at augmented pollinator habitat is needed to evaluate if these patterns will change over time.

Figure 1

Visual comparison of viral matrices. Each block shows samples from a particular location with A. mellifera (Am) [on the left-hand matrix of each block] and B. impatiens (Bi) [on the right-hand matrix]. Samples from 2017 are displayed at the top of each block and 2018 on the bottom. Each row represents an individual sample, and each column represents a different target listed in alphabetical order (A = ABPV; B = BQCV; C = CBPV; Da = DWVa; Db = DWVb; I = IAPV; L = LSV; T = Try. spp.; and N = Nos. spp.). Relative intensity is represented with a color gradient from low (bright yellow) to high (bright red). This figure was created using Adobe Illustrator, Microsoft Excel, and Microsoft Word. Thank you to Kirsten Benson for creating the base map.

Figure 2

Copy number per 1 µl of template (approximately 3.3 ng of RNA) of Trypanosome spp. for A. mellifera, B. impatiens, and B. pensylvanicus across the different levels of flower cover.

Figure 3

Copy number per 1 µl of template (approximately 3.3 ng of RNA) of Trypanosome spp. for A. mellifera, B. impatiens, and B. pensylvanicus across the sampling season.