Generalist solitary ground-nesting bees dominate diversity survey in intensively managed agricultural land

Abstract

In Western Europe agricultural management was intensified in the period 1950–2010 with negative consequences for ecosystem services, such as pollination, especially in countries with a large proportion of agriculture. Farmland represents 66% of the Danish landscape, but little is known about wild bees despite that 75% of the country’s wild and cultivated plant species depend on insect pollination. Strawberry (Fragaria × ananassa) gains considerable benefits from insect pollination and abundance, species richness and functional diversity, are all important elements. We surveyed the diversity of wild bees during strawberry flowering by sampling bees with pan-traps along permanent margins bordering strawberry fields on six organic and six conventional farms in eastern Denmark and compared the results of the survey with that of sampling site farming practice and field margin forage availability. The majority of bees sampled were polylectic solitary ground-nesting bees known to forage on species of the rose family. This indicates that these bee species are potential pollinators of strawberries, and the low number of specialized bees suggests that the bee community was affected by the simplified landscapes. Temporal trends in abundance, species richness, and body size of the bees, suggest that the functional diversity of pollinator assemblages available differed for early- and late-flowering strawberries. Fewer plants species and a lower plant cover were found in the margins of sprayed fields. Abundance and diversity of the wild bees were neither correlated with the use of herbicides and insecticides, nor with plant species richness or flowering plant cover.

Wild bee functional diversity and plant associations in native and conventional plant nurseries

“…We documented an effect of the native status of plants cultivated by nurseries on the functional distributions of wild bees present in nurseries, but no effect of landscape-level factors like nursery size or surrounding natural area. While most species and individuals detected were generalist, below ground-nesting, and solitary -as seems to be common in agricultural areas (Ahrenfeldt et al, 2019) -we also detected floral specialists, above-ground cavity nesters, and eusocial species. Moreover, we detected cleptoparasitic species, which serve as indicators of functionally diverse bee assemblages (Sheffield et al, 2013).…”

Interactions of local habitat type, landscape composition and flower availability moderate wild bee communities

“…Different disturbance regimes result in distinct plant communities that in turn shape wild bee communities (Hawkins et al 2015;Neumüller et al 2018). In this context it has been shown, that intensively managed agricultural landscapes are dominated by generalist ground-nesting bee species (Ahrenfeldt et al 2019). In concordance with this assumption, generalist ground-nesting species such as certain species of bumblebees, halictid bees and andrenid bees substantially contributed to the compositional dissimilarity between the three habitat types.…”

“…The positive effect of extensive grassland can also be ascribed to the associated reduction of intensive arable farming (Kremen et al 2002), as we have found that the proportion of extensively managed grassland is negatively correlated with those of arable land in the studied surroundings. In this context, an increased cover of tilled agricultural land has been shown to reduce bee richness and abundance by reducing floral resources on a landscape scale (Le Féon et al 2010;Ahrenfeldt et al 2019). Furthermore, pesticide seedcoating and spray drift on arable land can contaminate nearby non-target areas (Pimentel 1995;Brittain et al 2010;Botías et al 2016).…”

“…Thus, bee communities strongly depend on structurally rich landscapes that offer a variety of resources (Bommarco et al 2010). As a result, intensively managed agricultural landscapes, which offer a poor selection of floral resources, are dominated by relatively common, generalist bees (Wood et al 2017;Ahrenfeldt et al 2019;Grab et al 2019).…”

Plugging the hunger gap: Organic farming supports more abundant nutritional resources for bees at critical periods

“…The vast majority of the bees caught in this study were polylectic, i.e. plant generalists, which tend to dominate agricultural landscapes (Ahrenfeldt et al 2019). This generality may help to explain the similarity in bee communities despite the floral differences.…”