Pollinators in Virginia Cucurbits

Abstract

Cucurbita pepo plants (pumpkins and squash) are predominately monoecious, requiring pollinators for effective fruit set due to the separation of staminate and pistillate flowers. Consequently, growers often introduce managed pollinators, such as honey bees (Apis mellifera L.) and bumble bees (Bombus spp.), to enhance crop yields. This creates a complex dynamic of interactions between plants, managed pollinators, and native pollinators, particularly a native specialist bee, the squash bee (Xenoglossa pruinosa Say). This work integrates observational methods, analysis of bee microbiome compositions following exposure to C. pepo pollen, and characterization of viral dynamics within the C. pepo agroecosystem to address knowledge gaps regarding constraints on pollinator health and performance in Virginia cucurbit production. Pollinator observations were first conducted to develop a standardized method for quantifying pollinator communities at the field level, enabling growers and experts cooperatively to identify key pollinators and implement management strategies for pollinator protection. This goal was addressed in two chapters. The first demonstrated that visual observations differed from vacuum sampling and bowl trapping in their ability to detect the three primary pollinators in Virginia cucurbits: A. mellifera, Bombus spp., and X. pruinosa. The second chapter evaluated camera trapping relative to visual observations as a tool to facilitate grower and expert collaboration in pollinator identification. Results indicated no significant differences in morphotaxa groups observations of honey bees and bumble bees; however, there were differences in squash bees between methods of observation in the month of August. Subsequent work examined gut bacterial microbiomes of the three major bee types and assessed constraints encountered by social bees (Apis mellifera and Bombus impatiens Cresson) when exposed to C. pepo pollen. We observed a significant decline in the Firmicutes phylum of bacteria, in particular Lactobacillus spp., following consumption of C. pepo pollen in social bees. This suggests C. pepo may indirectly affect overall bee health by altering gut microbial composition and potentially reducing the bee's ability to utilize diverse food sources. Finally, we examined viral communities, including both plant and bee viruses, across cucurbit fields and associated pollinators. Results suggest that all major pollinator types may contribute to horizontal transmission of cucurbit plant viruses, and we identified potential hotspots for bee virus spillover within the C. pepo agroecosystem. Additionally, we report the detection of bee viruses within the cleptoparasite of squash bees and propose potential spillover routes to this parasite. Collectively, these findings highlight the need for further research to assess the ecological risks and benefits of introducing managed bees to Virginia C. pepo systems, for both pollinator and plant health.