Bombus terrestris: a more efficient but less effective pollinator than Apis mellifera across surveyed white clover seed fields

Abstract

White clover (Trifolium repens L.) seed crops require insects for pollination. Apis mellifera Linnaeus, 1758 are normally placed within fields but other insects might also be contributing additional pollination. To understand their potential contribution, we evaluated abundances across fields during peak flower; measured loose body pollen on four bee and two fly species and compared the rate of movement between inflorescences and florets for A. mellifera and B. terrestris (Linnaeus, 1758). A. mellifera were the most abundant verified flower visitor, although B. terrestris and long-tongued Bombus species also visited fields. Other insects recorded included Lasioglossum bees and two hover fly species, but these were considered ineffective pollinators (either low abundances or carried few pollen grains). B. terrestris were considered a more efficient pollinator than A. mellifera moving faster between florets but were less effective due to low abundances. Many Bombus spp. will forage under weather conditions unfavourable to A. mellifera, therefore, providing complimentary pollination.