Pollination Effectiveness of the Hoverfly Eristalinus aeneus (Scopoli, 1763) in Diploid and Triploid Associated Watermelon Crop

SIMPLE SUMMARY: Watermelon is an important crop worldwide. However, pollination is a challenge in new commercial seedless cultivars, exacerbated by the decline in pollinators and protected production systems. These negative factors affect yield due to pollination deficit. Therefore, a search for alternative pollinators is important, evaluating their pollination effectiveness. In this work, we studied the pollination of diploid and associated triploid seedless watermelon varieties using eristaline hoverflies, focusing on the characteristics of floral visits, pollen transport, and crop yield. We found that Eristalinus aeneus is an effective pollinator in watermelon at densities of 30 and 45 individuals per square meter. ABSTRACT: Watermelon (Citrullus lanatus) is an important crop worldwide. Pollination of this crop is carried out by insects, with honey bees (Apis spp.) and bumble bees (Bombus spp.) as the most used in greenhouse production. Nevertheless, due to the extreme conditions in closed enclosures, these hymenopterans suffer management and behavior problems leading to insufficient pollination. The effectiveness of three release densities (15, 30, and 45 individuals/m(2)) of Eristalinus aeneus was compared in diploid- and triploid-associated watermelon varieties under protected cultivation. Floral visits, pollen–pistil interaction after pollen transport, yield, and fruit quality were evaluated. The number of floral visits increased with release density in both pistillate and staminate flowers. No significant differences were observed, however, among release densities or between flower types in the duration of the visits. Floral preferences were not found in the behavior of E. aeneus in watermelon. High and medium release densities increased pollen deposition onto the stigma, and consequently the yield of the triploid variety compared to low release density, by 23.8 to 41.8% in 2020 and by 36.3 to 46.7% in 2021. The results of this trial demonstrate the potential of E. aeneus as a managed pollinator in protected cultivation of triploid watermelon.