a1 Department of Applied Biology, Pembroke Street, Cambridge
a2 Department of Zoology, Downing Street, Cambridge
In St Vincent, West Indies, the yellow passionfruit (known as Passiflora edulisf. flavicarpa Degener, but probably specifically distinct from P. edulis Sims) is grown commercially and is pollinated by the indigenous bee Xylocopa mordax Smith. The diel patterns of anthesis and nectar availability are described and related to the timing of bee visits and pollination. Flower-bagging experiments confirmed that the setting of fruit depended on cross-pollination, was prevented by exclusion of flower visitors, and was sometimes limited in the field by inadequate pollination.
Bees collected Passiflora nectar, and evaporated it on their tongues from 45–50 % to 62–63 % sugar before storing it. But the Passiflora pollen deposited on the bee's dorsum was groomed off and rejected; only Gliriddia pollen was used for bee bread. Thus the bees treated ‘acceptable’ (Gliriddia) pollen and ‘unacceptable’ (Passiflora) pollen differently, and since pollen unacceptability improves the pollen's chance of reaching a stigma, it may be a widespread adaptation.
The yellow passionfruit flower shows many features characteristic of tropical Xylocopa flowers. Here, as elsewhere, this introduced crop depends for its pollination on indigenous bees which, though suitable morphologically and behaviourally, are not abundant enough to cause a high proportion of flowers to set fruit. The setting of fruit might be improved by increasing bee populations through provision of more timber for nestsites, and suitable flowers to supply pollen and nectar throughout the year.
(Received May 26 1980)