Cucurbit crops in temperate Australia are visited more by native solitary bees than by stingless bees

Abstract

The propagation and management of stingless bees for pollination services is a growing industry in Australia, but we need to better understand in which crops and environments these pollinators are most useful. We investigated the potential of two Australian stingless bee species, Tetragonula carbonaria and Tetragonula hockingsi, to pollinate cucumber and watermelon crops in both field and protected cropping (greenhouse or polytunnel) environments. We recorded floral visitation rates and fruit yield in cucumber and watermelon and characterized the assemblage of wild pollinators visiting both field-grown crops. Of 229 surveys of cucumber flowers and 144 surveys of watermelon flowers in field experiments where T. carbonaria colonies were deployed, no stingless bees were recorded visiting cucumber flowers, and only one was recorded visiting watermelon flowers. Visitor assemblages in both crops were dominated by the introduced Apis mellifera, with a high number of native solitary halictid bees also visiting watermelon flowers. In a no-choice experiment, stingless bee (T. carbonaria and T. hockingsi) visits to watermelon flowers in a polytunnel occurred after four days but were low in number at first, compared to a greenhouse experiment where visits to cucumber flowers occurred only after 22 days and resulted in poor fruit set. In fact, T. hockingsi more readily collected fungal spores than pollen from cucumbers. Our results indicate that T. carbonaria and T. hockingsi do not make major contributions to the pollination of cucumber and watermelon, but other native flower visitors, including halictid bees, may be important pollinators of these crops.