The role of native and exotic bees in Cucurbita maxima var. zapallito pollination: the effects of pollination intensity and visits on commercial fruits

Abstract

We conducted experimental pollinations, controlled visits, and observed pollinators’ behaviour to identify activity supporting Cucurbita maxima var. zapallito fruit production. We predict that (a) stigmas artificially pollinated with pinned native bees (Eucera fervens) will have more pollen grains and will produce heavier commercial fruits than those pollinated with exotic bees (Apis mellifera); (b) the differences in fruit weight between the native and exotic bees are expected to increase with the intensity of artificial pollination; (c) controlling E. fervens visits in natural pollination will show fruit trends similar to artificial pollination. Unlike A. mellifera, E. fervens reached flowers by contacting stigmas or the anthers with their abdomen, depositing more pollen grains (> 80) than A. mellifera. Artificial pollination treatments with the two pinned-bee types resulted in fruits of similar weights regardless of pollination intensity. Conversely, in natural pollination, weight differences were observed when the number of visits increased. E. fervens provided at least 132 pollen grains with > 3 visits: the threshold necessary for producing commercial fruits. The visitation frequency registered exceeded this minimum reaching one visit every 10 min. Other factors, such as pollination date and plant, influenced fruit production. Few visits are enough for obtaining commercial fruits: being an immature fruit, squash does not require seed development, besides species with separate flowers developed strategies to achieve rapid pollen saturation. Squash crops rely on the ecological pollination service provided by bees underscoring the conservation value of native bee species.