Investigating bee dietary preferences along a gradient of floral resources: how does resource use align with resource availability?

Bee dietary preferences, or the floral resources that they consistently collect, likely impact where a species can persist. For this reason it is likely that bee dietary preferences are dependent upon the composition of the plant community. In this study, we evaluated floral visits and pollen loads of the mining bee, Andrena angustitarsata Viereck, across a 630 km north-south range to understand dietary preferences along a floral resource gradient. Previous research, in a more geographically limited area, suggested this species was an eclectic oligolege on predominantly Apiaceae and in part Rosaceae. In the present study we found the species predominately visited and collected pollen from Apiaceae and Rosaceae, but visited 12 flower families and collected pollen from 32, distinguishing them as generalist foragers. The frequency of Apiaceae pollen on the bees and the species-level specialization index (a measure of visit specialization) were higher in regions with higher Apiaceae abundance. In addition Apiaceae and Rosaceae were the only plant families significantly preferred for pollen collection, regardless of floral abundance. We conclude that across our study region A. angustitarsata has a generalist dietary breadth, but also has dietary preference for Apiaceae and Rosaceae. Our study indicates that while bees may overall make generalist foraging decisions they may still prefer and likely benefit from selecting fewer flower taxa.

Hummingbirds and bumble bees exposed to neonicotinoid and organophosphate insecticides in the Fraser Valley, British Columbia, Canada.

To measure exposure to neonicotinoid and other pesticides in avian pollinators, we made novel use of cloacal fluid and fecal pellets from rufous (Selasphorus rufus) and Anna's (Calypte anna) hummingbirds living near blueberry fields in the Fraser River Valley and Vancouver Island, British Columbia, Canada. To examine on-farm exposure to pesticides in invertebrate pollinators, we also collected bumble bees native to Canada (Bombus mixtus, Bombus flavifrons, and Bombus melanopygus), their pollen, and blueberry leaves and flowers from within conventionally sprayed and organic blueberry farms. By sites and sample type, the results reported in the present study represent pooled samples (n = 1). In 2015 to 2016, the combined concentration of the neonicotinoid insecticides imidacloprid, thiamethoxam, and clothianidin detected in hummingbird cloacal fluid from sites near conventionally sprayed blueberry fields was 3.63 ng/mL (ppb). Among the 18 compounds measured in fecal pellets, including one neonicotinoid (imidacloprid), only piperonyl butoxide was detected (1.47-5.96 ng/g). Piperonyl butoxide is a cytochrome P450 inhibitor applied with some insecticides to increase their toxic efficacy. Only diazinon was detected in bumble bees (0.197 ng/g), whereas diazinon (1.54-1.7 ng/g) and imidacloprid (up to 18.4 ng/g) were detected in pollen collected from bumble bees including the bees from organic sites located near conventionally sprayed blueberry farms. Imidacloprid was also detected at 5.16 ng/g in blueberry flowers collected 1 yr post spray from 1 of 6 conventionally sprayed blueberry farms. Environ Toxicol Chem 2018;37:2143-2152. © 2018 SETAC.

Pollen Foraging Differences Among Three Managed Pollinators in the Highbush Blueberry (Vaccinium corymbosum) Agroecosystem.

Highbush blueberry, Vaccinium corymbosum (Gray), production in British Columbia is dependent upon insect pollination for fruit yield with particular cultivars demonstrating low yields due to poor pollination. New managed species of pollinators are being developed to provide farmers with managed pollinator options beyond Apis mellifera (Linnaeus). Pollinators in highbush blueberry agricultural systems encounter a variety of nontarget floral resources that may affect the pollination received by the crop. Our study analyzed the differences in pollen foraging of honey bees and two species of managed bumblebees across nine farm sites. Corbicular pollen loads from pollen foraging workers were removed and identified to the lowest taxonomic level possible. Of the three managed pollinators, the corbicular pollen loads of Bombus huntii (Greene) contained the most blueberry pollen (52.1%), three times as much as the two other managed bee species. Fifteen morphotypes of pollen were identified from all foraging workers with Rosaceae being the most frequently gathered overall pollen type (n = 74). The noncrop pollen identified in our samples derived from plant species not common as weedy species in the agroecosystem suggesting that floral resource diversity outside of the farm boundaries is important to pollinators. The three managed species in our blueberry fields utilized floral resources differentially underscoring the importance of pollinator species' characteristics and large-scale floral resource landscape in developing new managed pollinators and pollination strategies.