Social Organization and Pollination Efficiency in the Carpenter Bee Xylocopa pubescens (Hymenoptera: Apidae: Anthophorinae)

Abstract

Many agricultural greenhouse crops suffer reduced yields due to insufficient pollination. This problem can be alleviated by introducing efficient pollinating insects into the greenhouse. The bee Xylocopa puhescens Spinola 1838, a candidate for domestication as an agricultural pollinator, is unique in its facultative social organization. Females either nest solitarily, or together with a second female (a non-reproducing guard). Social nesting occurs when food and nest sites are limited, and carries fitness benefits and costs to the bees as.compared to solitary nesting. The implications of X pubescens' social organization for crop pollination were investigated. Honeydew melons were grown as a model crop in a small greenhouse. The non-crop plants Portulaca oleracea L, Solanum rantonnetii C. Lavandula angustifolia Mill and Ocimum basilicum L supplemented the bees' diet. Social and solitary X pubescens nesters were introduced into the greenhouse in alternation. The bees' daily activity pattern, the frequency and duration of visits to each flower species, and the run-lengths of consecutive visits to each flower species were recorded. The melons' fruit set, and the fruits' mass and seed number, were determined. Social nesters visited P oleracea more frequently than solitary bees when this species was in bloom. After P oleracea finished blooming, socially nesting bees visited melon more often than solitary nesters Social bees spent a longer time at the melon patch and tended to be more flower constant than solitary nesters, but spent less time per flower than solitary individuals. Solitary and social bees did not differ in their daily activity patterns and flower visitation rates. Pollination by both types of nesters resulted in similar fruit sets, fruit mass and fruit seed numbers. The dissimilarities in foraging behaviour may reflect differences in the dietary demands of solitary vs social nesters. The similarity in fruit sets and flower constancy suggests that both nest types provide pollination services of similar quality.