Diversity of hoverflies and their floral visitation patterns in cultivated cucurbit crops in Morogoro, Tanzania

Hoverflies (Diptera: Syrphidae) provide valuable ecosystem services, such as pollination, to a large variety of wild and cultivated sexually reproducing plant species. In this study, we examined the diversity, number of visits, visitation rate and foraging time of hoverfly species in three main cucurbit crops (cucumbers (Cucumis sativus L.), watermelons (Citrullus lanatus (Thunb.) Matsum & Nakai) and squash (Cucurbita moschata D.)) in two agroecological zones (mountainous and plateau) of the Morogoro region in Tanzania, between March and July 2020. We recorded 801 hoverflies of 12 species, of which the most common were Toxomerus floralis (Fabricius, 1798) (37.7% of total records), Eristalinus megacephalus (Rossi, 1794) (25.3%) and Mesembrius caffer (Loew, 1858) (16.4%). Hoverfly diversity was significantly higher in watermelon and squash crops within the mountainous zone as compared to the plateau zone. Toxomerus floralis was the most frequent visitor across all crops and agroecological zones. Eristalinus megacephalus showed a higher visitation frequency than M. caffer in cucumber and watermelon in the mountainous zone. Visitation rates for E. megacephalus, T. floralis and M. caffer were markedly higher in the mountainous zone than in the plateau zone. Of all hoverfly species, T. floralis displayed the longest foraging times in the mountainous zone. Seasonality appeared to have no significant impact on foraging duration and number of flower visits. These findings provide a valuable baseline for understanding hoverfly diversity and foraging behaviour on cucurbit crops and serve as a crucial stepping stone towards a deeper understanding of hoverfly feeding behaviour and its implications for agriculture. Additional studies are required to describe the actual role in pollination of the hoverflies and the factors that may enhance their potential as pollinators of cucurbit crops.