COS 156-4 - Evaluating the effects of multiple pollinator visits on conspecific and heterospecific pollen transfer

Abstract: Most wild plants and many global food crops are dependent on insect pollination services to achieve better yield and fruit quality. However, the ability of floral visitors to effectively transfer compatible pollen between flowers and onto stigmas can vary considerably. We studied the pollination services provided by European honey bees (Apis mellifera) and native Australian stingless bees (Tetragonula carbonaria) to three model crops that require pollination to set marketable fruits: blackberry (Rubus fruticosus), blueberry (Vaccinium virgatum), and raspberry (Rubus idaeus). First, we examined if the number of pollinator visits affect the number of conspecific and heterospecific pollen transferred and the species richness of pollen deposited on berry stigmas. Second, we evaluated if the composition of the pollen deposited by both pollinators differed to pollen transferred from single species alone. To do this, we bagged virgin flowers and observed the number of flower visits by individuals of each pollinator species. We then collected and processed stigmas that received multiple visits (1, 2, 3, 4 or 5) by honey bees, stingless bees, and mixed visits (both species) and analysed the pollen transferred by identifying the pollen and counting the number of conspecific and heterospecific pollen grains. We found that the amount of conspecific pollen was related to pollinator species identity and visit number, with native stingless bees depositing greater amounts than honey bees or mixed visits. The amount of pollen increased following each visit. Heterospecific pollen deposition was not related to pollinator species identity and was related to visit number in blueberry only, with an increase in heterospecific pollen until the third visit by honey bees and mixed visits, and subsequently decreasing with additional visits. Even though honeybees were more abundant flower visitors overall than stingless bees, ratios of conspecific and heterospecific pollen deposition indicate stingless bees and mixed visits ensure greater conspecific pollen deposition. This study suggests that management practices to support the integrated management of both honey bees and native insects will enhance effective pollination services for blackberry, blueberry, and raspberry.