Pollination of kiwifruit (Actinidia deliciosa) by bumble bees (Bombus terrestris): effects of bee density and patterns of flower visitation.

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Abstract
Flowering male and female vines of kiwifruit (Actinidia deliciosa Chev.) were caged and provisioned with small colonies of Bombus terrestris (Hymenoptera: Apidae). Fruit weight and seed number in the seven cages increased with increasing bee density. The heaviest fruit were associated with a foraging density of one bee per thousand female flowers. Although bumble bees displayed a greater fidelity towards kiwifruit pollen collection than did honey bees (Apis mellifera L.), fidelity to kiwifruit in both species appeared to be influenced by the presence and composition of competing bloom. White clover (Trifolium repens) was a major competing species for honey bees and lupin (Lupinus arboreum) for bumble bees. Bumble bees exhibited a greater degree of crossover between male and female flowers than honey bees, based on an examination of male and female pollen in corbicular loads. Frequent crossover appears to facilitate the carryover of viable pollen from pollen-fertile staminate to pollen-sterile pistillate flowers. Tentatative suggestions are made for stocking rates.