Honey bees are the most abundant visitors to Australian watermelon but native stingless bees are equally effective as pollinators.
Despite the benefits of a diverse approach to crop pollination, global food production remains reliant on a low diversity of managed pollinators, especially the European honey bee (Apis mellifera). To facilitate more robust pollinator management and improve the resilience of the production system, it is necessary to understand regional variation in the pollination ecology of global food crops. Watermelon (Citrullus lanatus [Thunb.]Matsum&Nakai) is a highly insect pollinatordependent crop and even though it is grown globally across many different climate zones, little is known about its pollination ecology across the diverse growing regions of Australia, spanning from the tropics to the arid zone. We compared the species composition, visitation rates and effectiveness of the dominant floral visitors on 15 farms across fivemajor watermelon-growing regions of Australia. We found that insect species composition differed significantly among regions, but honey bees were the dominant watermelon flower visitor, with relative abundance varying from 73% to 94%. However, native bees (including stingless bees Tetragonula sp., and bees from families Megachilidae and Halictidae such asLasioglossum, Homalictus and Lipotriches) and flies (particularly Syrphidae sp.) also visited and transferred pollen onto watermelon flowers. In particular, native stingless bees were common visitors in several growing regions and deposited similar amounts of pollen to honey bees. Our findings indicate that the Australian watermelon industry utilizes honey bees, but the diverse assemblage of available native pollinating taxa provides an additional opportunity for growers in specific growing regions. Pollination service delivery could be increased by deploying managed populations (e.g., native stingless bee colonies), employing pollinator-safe land management practices as well as exploring methods for increasing the efficiency of managed honey bee colonies.