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

1. Aspects of the flowering biology of wild cashew Anacardium occidentale, an andromonoecious, self-fertile tree, were studied in the north-east of Brazil, where this species is endemic. Comparison was made among two bee species, Apis mellifera and Centris tarsata, in their pollination of cashew flowers using a number of measures including single bee visits to marked flowers. 2. Cashew flowering is protandrous within a day. Male flowers greatly outnumber hermaphrodite flowers. Stigmas lose receptivity rapidly and pollen is quickly removed from anthers yet flowers remain intact for several days. 3. 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 two bet species under investigation when visiting hermaphrodite cashew flowers suggests that they may both act as good pollinators. 4. We develop an index of efficiency of pollen removal from anthers (PREi) whereby the relative benefits of flower visitors to a component of a plant's male reproductive success can be quantified. 5. Comparisons of single bee visits to flowers with unvisited flowers and others receiving unlimited visits were used to show that: C. tarsata pollen collectors were more efficient than nectar collectors of either bee species at removing pollen from anthers: nectar collectors of both bee species had similar pollen removal efficiencies; C. tarsata was more efficient at depositing pollen on stigmas than A. mellifera; both bee species had statistically similar efficiencies at setting seed. 6. The indices of efficiency for some of the stages in the pollination of cashew suggest that C. tarsata flower visits may enhance plant reproductive success over flower visits by A. mellifera but that both bee species may be suitable for the pollination of commercially grown cashew. 7. Despite cashew's single ovule per 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.