A comparison of two pollinators: the introduced honey bee Apis mellifera and an indigenous bee Centris tarsata on cashew Anacardium occidentale in its native range of NE Brazil.
Abstract
Aspects of the flowering biology of wild cashew A. occidentale, an andromonoecious, self-fertile tree, were investigated in north-east Brazil, where this species is endemic. The pollination of A. occidentale by the 2 bee species, A. mellifera and C. tarsata, was compared. Cashew flowering is protandrous within a day. Male flowers greatly outnumber hermaphrodite flowers. Stigmas lose receptivity rapidly, and pollen is quickly removed from anthers although flowers remain intact for several days. Only females of C. tarsata collected pollen from cashew flowers, and then only from male flowers. The similar foraging behaviour of the nectar collectors of the 2 bee species on these flowers suggested that they may both act as good pollinators. An index of efficiency was used of pollen removal from anthers, and the relative benefits of flower visitors to a component of the male reproductive success of the plant were quantified. Single bee visits to flowers, unvisited flowers and flowers receiving unlimited visits were compared. C. tarsata pollen collectors were more efficient than nectar collectors of either bee species at removing pollen from anthers, and nectar collectors of both species had similar pollen removal efficiencies. C. tarsata was more efficient at depositing pollen on stigmas than A. mellifera, and both species had statistically similar efficiencies for seed setting. The indices of efficiency for some of the stages in the pollination of cashew suggested that C. tarsata flower visits may increase plant reproductive success compared with flower visits by A. mellifera, but that both bee species may be suitable for the pollination of commercially grown cashews. Despite the fact that cashews have 1 ovule/flower, high nut set demands a high rate of pollinator visitation during the peak time of stigma receptivity. Provision of additional bee pollination in commercial orchards is recommended to obtain good nut yields.