Differential responses of ground-nesting bees (Leioproctus paahaumaa and Lasioglossum spp.) to horticultural intensity and landscape factors

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Habitat loss and increased pesticide use associated with intensified agriculture contribute to declines in wild bees. The vast majority of bee species worldwide are living below ground, yet their responses to agricultural practices are poorly understood. We surveyed New Zealand native ground-nesting bees ( Lasioglossum sordidum , Lasioglossum cognatum and Leioproctus paahaumaa ) in eight avocado orchards across a gradient of horticultural intensity. We examined how bee abundance related to pesticide use, land cover, soil hardness, and slope. Total bee abundance was negatively associated with slope, and positively associated with horticultural intensity and soil hardness. Lasioglossum sordidum were more abundant in high intensity horticultural areas, but declined with higher pesticide use. In contrast, although L. paahaumaa abundance was highest in low intensity horticultural areas, their abundance was predicted best by models that only included slope and soil hardness. No significant predictors were identified for L. cognatum . These species-specific responses to landscape factors and farm management practices highlight the challenge of identifying agricultural practices that will support ground-nesting bees. Nevertheless, reducing pesticide use will promote at least L. sordidum populations and therefore facilitate the adoption of sustainable farming methods to enhance ecosystem health.