Hoary Squash Bees (Eucera pruinosa: Hymenoptera: Apidae) Provide Abundant and Reliable Pollination Services to Cucurbita Crops in Ontario (Canada)

Abstract

The increasing demand for insect-pollinated crops highlights the need for crop pollination paradigms that include all available pollinators. In North America, Cucurbita crops (pumpkin, squash) depend on both wild (solitary and Bombus spp.: Hymenoptera: Apidae) and managed honey bees (Apis mellifera L. 1758: Hymenoptera: Apidae) for pollination. Temporal and spatial differences in abundance may determine which bee taxa are the most important pollinators of Cucurbita crops. We surveyed bees visiting Cucurbita crop flowers on 19 farms over four years (2015–2018) during the crop flowering period (July 1–August 30 from 06:00–12:00). All the farms surveyed had hoary squash bees (Eucera pruinosa (Say, 1867), and most also had some combination of honey bees, bumble bees (Bombus spp.), or other wild bees present on their Cucurbita crop flowers. All four bee taxa were present on about two-thirds of farms. Spatially and temporally, wild bees were more abundant on Cucurbita crop flowers than managed honey bees. Hoary squash bees were the most abundant wild bees, maintaining their abundance relative to other wild bee taxa year-over-year. Male hoary squash bees were both more frequently and consistently seen visiting crop flowers than females in all years. Peak activity of hoary squash bees and bumble bees coincided with the daily crop pollination window, whereas peak activity of honey bees and other wild bees occurred after that window. In addition to elucidating the ecological interactions among wild and managed pollinators on Cucurbita crops, our work provides a novel practical way to evaluate pollinator abundance using a crop-centered benchmark framework.

Quantifying exposure of bumblebee (Bombus spp.) queens to pesticide residues when hibernating in agricultural soils

“…In Southern Ontario, agricultural field margins appear to provide bumblebees with food, nesting, and hibernating resources comparable to those of semi-natural habitats (Purvis et al 2020). Bumblebees are common visitors of apples, berries, squash, and many other crops and, as such, are likely to hibernate near farms growing these crops (Blaauw & Isaacs 2014; Gervais 2021; Willis Chan & Raine 2021). Here, we quantified pesticide residues in agricultural soils to understand exposure for hibernating bumblebee queens and compared these residues between apple orchards and diversified farms, two cropping systems commonly encountered in Ontario and differing in their pesticide use patterns.…”

Phenological synchrony between the hoary squash bee (Eucera pruinosa) and cultivated acorn squash (Cucurbita pepo) flowering is imperfect at a northern site

“…The timing of planting of Cucurbita crops in Ontario is constrained in the spring by soil temperature and risk of frost, generally occuring in late May or early June. Although bloom begins in July, pistillate (fruit-bearing) flowers do not appear until early August, marking the beginning of the crop pollination window ( Willis Chan & Raine, 2021a ). The timing of harvest is constrained by the time it takes squash or pumpkins to mature after pollination (∼60 days) and the timing of the biggest markets for the fruit, which are Thanksgiving (early October in Canada) and Halloween (October 31st) ( Westerfield, 2014 ).…”

“…The timing of harvest is constrained by the time it takes squash or pumpkins to mature after pollination (∼60 days) and the timing of the biggest markets for the fruit, which are Thanksgiving (early October in Canada) and Halloween (October 31st) ( Westerfield, 2014 ). Working backwards 60 days from an October 15 th harvest date, Cucurbita flowers would have to be pollinated by August 15 th in order to set marketable fruit in Ontario, marking the end of the crop pollination window, although flowering continues after this ( Willis Chan & Raine, 2021a ).…”

“…As a pollen specialist, the foraging activity of hoary squash bees corresponds seasonally to bloom of wild and/or cultivated Cucurbita , though their activity period is variable across their range. For example, in California, Utah, and Mississippi, hoary squash bees are active on Cucurbita crops in May and remain active over a two-month period, but in Ontario at the northern edge of the species’ range, hoary squash bees are active between mid July and the end of August ( Figure 1 ) ( Hurd et al., 1974 ; Willis & Kevan,1995 ; Cane et al., 2011 ; Willis Chan & Raine, 2021a ). Squash bees are matinal foragers, avoiding competition by acquiring squash or pumpkin floral resources before other bee species begin to forage on the crop ( Willis Chan & Raine, 2021a )…”

“…Although important itself, the hoary squash bee has a wider significance. Because of its commonness, ubiquity across a large range, and ease of maintenance in captivity under field-realistic conditions, it may be the best model species available to represent other more elusive ground-nesting bees in agricultural pesticide risk assessments that are presently honey bee centric ( Willis Chan et al., 2019 ; Franklin & Raine 2019 ; Willis Chan & Raine, 2021a ,b). However, compared to the honey bee, we have very little information about the hoary squash bee.…”