Preference of Peponapis pruinosa (Hymenoptera: Apoidea) for Tilled Soils Regardless of Soil Management System

Abstract

Concerns about global pollinator declines have placed a growing focus on understanding the impact of agriculture practices on valuable native pollinators in these systems. Cultivation practices such as tillage disturb agroecosystems and can have negative impacts on ground-nesting pollinators. The squash bee, Peponapis pruinosa (Say), is a ground-nesting specialist pollinator of Cucurbita (Cucurbitaceae) crops (i.e., pumpkins and squash) that often nests in agricultural fields and thus may be vulnerable to these practices. We investigated the impact of tillage on nesting behavior of P. pruinosa in plasticulture and strip-tilled squash systems. We used choice experiments to test nesting substrate preference and nesting success of caged P. pruinosa in two soil tillage systems: strip tillage and plasticulture. The strip tillage system comprised two tillage zones (strip-tilled row with no-till edges), and the plasticulture system comprised two tillage zones (plastic bed and conventional tillage edge). The results of our study indicate that P. pruinosa nesting density did not significantly differ between the strip tillage and plasticulture systems. Within each system, P. pruinosa preferred excavating nests in the most disturbed soil zones (strip-tilled row and conventionally tilled edge). In the strip tillage system, the strip-tilled row had significantly more nests than the no-till edge. Results of these studies suggest that soil tillage practices can influence P. pruinosa nesting choice and production practices should be considered when developing a pollinator protection plan.

Nesting habitat of ground‐nesting bees: a review

“…It is certainly the case that dietary specialists (oligoleges) nest near their host plants: squash bee ( Peponapis pruinosa (Say), Apidae) nests occur in squash ( Cucurbita spp.) fields (Julier & Roulston, 2009; Skidmore et al ., 2019); Nomia melanderi nest near alfalfa ( Medicago sativa (Linnaeus)) (Cane, 1997, 2008; Vinchesi et al ., 2013); and Dieunomia triangulifera nest near sunflowers ( Helianthus annuus (Linnaeus)) (Minckley et al ., 1994). Oddly, however, it is not known whether bees actually use the presence or abundance of host‐plant flowers or foliage when choosing where to nest: they may simply be found alongside their host‐plants because of philopatry, or because they share substrate preferences with their host‐plants.…”

“…Such research would be especially valuable in agricultural systems, where farming practices can involve mixing the soil to a depth of up to 40 cm during tillage, and the use of agrochemicals to combat insect pests. A few papers have investigated the effect of tillage (Ullmann et al ., 2016; Skidmore et al ., 2019), irrigation (Julier & Roulston, 2009) and pesticides (Willis Chan et al ., 2019) on ground‐nesting bees, but more research is needed on different species of ground‐nesters, other than squash bees, and their reproductive output. We still know little about the effects of agrochemicals on survival of ground‐nesting bees, whether at the underground larval stages or as adults, but recent studies have begun to show impacts of pesticides on bees through exposure to contaminated soil (Anderson & Harmon‐Threatt, 2019; Willis Chan et al ., 2019).…”

Pollination Is Sufficient, Even with Low Bee Diversity, in Pumpkin and Winter Squash Fields

“…The decline in numbers of squash bees is alarming because in 2014 and 2015 we began the hourly bee counts two hours earlier in order to better capture squash bee activity, based on reports in the literature that squash bees started visiting flowers at dawn [12,21], but the numbers of squash bees observed continued to decline. Chan et al [24] found that levels of neonicotinoids found in field soil from seed treatments and soil applications posed a significant hazard through soil contact to squash bees, which nest in the ground, preferring to nest in disturbed soil in cultivated fields [25].…”

Citizen science improves our understanding of the impact of soil management on wild pollinator abundance in agroecosystems

“…Conversely, another study observed similar adult squash bee abundance in tilled and untilled pumpkin fields, and squash bees preferred to nest in irrigated soil near host plants regardless of whether or not the soil was tilled [33]. However, more recent findings suggest that squash bees prefer to nest in tilled soil [34]. Mulching is another ground management practice commonly used in Cucurbita production that may deter or inhibit squash bee nesting.…”

“…Although multiple studies have examined the impacts of farm management on squash bees, the scope of investigation has often been limited to one management practice at a time, sample sizes have been relatively low, and results have often been mixed [31][32][33][34]. Here, we used a citizen science survey to determine how squash bee abundance varies according to multiple farm management practices including tillage type, depth, and mulch, and ascertain the distribution of squash bees in Michigan.…”