Abstract/Summary

There is increasing evidence in the literature of the importance of wild ground-nesting bees as pollinators of crops, especially for apple pollination. The survival of bees heavily depends on the availability of suitable food and nesting resources. Ways to provide floral resources are well established, however the nesting preferences of ground-nesting bees are poorly understood. This is a significant knowledge gap when considering that that three quarters of all wild bee species in the UK are ground nesters. This PhD used a combination of field surveys and manipulative experiments to address this gap with a focus on apple pollinators. In the UK the predominant apple pollinators are spring Andrena species. The first study used artificially prepared plots of bare soil to attract ground-nesting bees to nest in orchards in the south east of England. Nine soil parameters were measured to determine the preference of ground-nesting bees: hydraulic conductivity, soil compaction, soil moisture, soil temperature, soil stoniness, soil organic matter, soil root biomass, soil texture and vegetation cover. Eighteen non-parasitic ground-nesting bee species (7 Andrena, 9 Lasioglossum, 1 Halictus and 1 Colletes spp.) were recorded founding nests in the study plots. Soil stoniness and soil temperature were positively correlated, and vegetation cover and hydraulic conductivity were negatively correlated, with the number of ground-nesting bees on the plots. The second study used transect surveys to determine which ground-nesting bee species nest in apple orchards, and to identify their preferred orchard (alleyways, under trees, edges) and local (vegetation cover) nesting habitats. Fifteen non-parasitic ground-nesting bee species (12 Andrena spp., 2 Lasioglossum spp., 1 Halictus spp.) were recorded, nesting mainly under trees (36 %) and hedgerows (52 %) of apple orchards. Local habitat was a significant predictor of nest density, and bees mostly nested in areas of short grass (32 %), bare ground (31 %), and moss cover (18%). Andrena haemorrhoa Fabricius and Andrena nitida Müller nesting aggregations were also found under hedgerows of some apple orchards; these species have demonstrated a nesting preference for highly vegetated habitats. The nine soil parameters measured in the first study were also recorded for this study. Soil stoniness and soil temperature were positively correlated, and soil moisture was negatively correlated, with the nest numbers of nesting aggregations. The third study used artificially constructed nest sites (90 litre tree tubs filled with soil) to establish the preferred soil compaction (determined from the other studies) and other abiotic factors for bee nesting. The study attracted three non-parasitic bee species (1 Megachile, and 2 Lasioglossum spp.) to nest, but the great majority of attracted ground-nesters were wasp species (95.3% of total specimens). Pebble treatments were added to half the area of the soil surface in in each tub during the fourth year of the study, which attracted a significantly higher number of bees/wasps to nest compared to the bare soil without pebbles. Soil temperature, compaction and pebbles were positively correlated, and soil moisture was negatively correlated, with the nest density of soil tubs. Understanding wild bee nesting needs is an important component for the success of agri-environment schemes aiming to safeguard biodiversity and ecosystem services. Such knowledge would enable landowners and farm managers to create and maintain nesting habitats for wild bees and, with the provision of suitable food resources, contribute to the increase and diversification of bee populations. The findings of this PhD inform management practices on the nesting preferences of ground-nesting bees and provide recommendations on creating and maintaining nesting habitats for important crop pollinators in agricultural settings.