Contribution of bees and other pollinators to watermelon (Citrullus lanatus Thunb.) pollination

Watermelon (Citrullus lanatus Thunb.) is an important economic crop with 29.6 million tons produced worldwide. However, few native bees and other pollinators have been documented to visit watermelon flowers and the contribution of these insects to watermelon pollination has yet to be determined. We examined 40 commercial watermelon fields from 2013 to 2016 and obtained information on pollinator visitation rates for managed and wild pollinators at different distances from field margins. We determined the amount of pollen on common pollinators' bodies, how much time these pollinators spent on flowers, and the amount of pollen they deposited on stigmas. Forty-three species of potential pollinators were documented during the 4-year study. Managed honey bees (Apis mellifera L.) were the most common visitor, but numerous other pollinators (e.g., Agapostemon splendens Lepeletier, Campsomeris plumipes var. fossulana Fabricius) were found to be abundant. This sweat bee and scoliid wasp carried as much watermelon pollen as worker A. mellifera did. No differences were detected among visitation rates among various taxonomic groups at different distances (0, 25, 50, 100m) from field margins except for small bees (e.g., Lasioglossum, Halictus), which were found in higher abundances at the field margins. Managed and wild bumble bees (Bombus spp.) were not common visitors of watermelons and may not be a good surrogate for managed honey bees. Overall, numerous insect species contribute to watermelon pollination. Therefore, watermelon growers should consider future land-use changes or other management practices that might positively affect the abundances of bee and wasp species.