Abstract

Highbush blueberry yields are dependent on pollination by bees, and introduction of managed honey bees is the primary strategy used for pollination of this crop. Complementary pollination services are also provided by wild bees, yet highbush blueberry is increasingly grown in regions outside its native range where wild bee communities may be less adapted to the crop and growers may still be testing appropriate honey bee stocking densities. To contrast crop pollination in native and non-native production regions, we sampled commercial ‘Bluecrop’ blueberry fields in British Columbia and Michigan with grower-selected honey bee stocking rates (0–39.5 hives per ha) to compare bee visitors to blueberry flowers, pollination and yield deficits, and how those vary with local- and landscape-scale factors. Observed and Chao-1 estimated species richness, as well as Shannon diversity of wild bees visiting blueberries were significantly higher in Michigan where the crop is within its native range. The regional bee communities were also significantly different, with Michigan farms having greater dissimilarity than British Columbia. Blueberry fields in British Columbia had fewer visits by honey bees than those in Michigan, irrespective of stocking rate, and they also had lower berry weights and a significant pollination deficit. In British Columbia, pollination service increased with abundance of wild bumble bees, whereas in Michigan the abundance of honey bees was the primary predictor of pollination. The proportion of semi-natural habitat at local and landscape scales was positively correlated with wild bee abundance in both regions. Wild bee abundance declined significantly with distance from natural borders in Michigan, but not in British Columbia where large-bodied bumble bees dominated the wild bee community. Our results highlight the varying dependence of crop production on different types of bees and reveal that strategies for pollination improvement in the same crop can vary greatly across production regions.

Highlights

  • There is currently great interest in developing farm management practices to support sustainable crop pollination strategies that maximize yields

  • There was no significant difference in total flower-visitor or total bee abundance with distance from natural borders (total bees: K-W, χ2 = 1.3 (BC), 3.9 (MI), df = 3, p > 0.2, both regions)

  • In Michigan, but not British Columbia, wild bees and the subset of wild bees excluding Bombus spp. varied significantly with distance from natural borders (K-W, χ2 = 27.3, df = 3, p < 0.0001 [both tests]), with wild bee abundance significantly reduced at 50 m (M-W, U = 239, Tukey honest significant difference (HSD) p < 0.007) and 100 m (M-W, U = 238, Tukey HSD p < 0.002) compared to bee abundance at field borders

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Summary

Introduction

There is currently great interest in developing farm management practices to support sustainable crop pollination strategies that maximize yields. This is driven in part by concerns over the long-term availability and cost of managed bees, the honey bee (Apis mellifera L.), and by evidence for declines in the populations of some wild bee species from regions of agricultural production [1]. Diversified crop systems and those set within diverse landscapes have more abundant wild bee communities that can contribute to higher levels of crop pollination [5]

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