Syrphids feed on multiple patches in heterogeneous agricultural landscapes during the autumn season, a period of food scarcity

Many syrphid larvae are predators and have an important role as biological control agents of pests in agroecosystems. However, adults feed on non-prey resources such as pollen from flowers. Heterogeneous landscapes can provide syrphids with a great biodiversity of plants and ensure the existence of food resources. This is particularly important during periods of food scarcity, such as autumn, for syrphid species that spend those periods as adults. Nevertheless, the feeding habits of syrphid adults in resource-scarce agroecosystems are poorly known. In this study, the pollen consumption and preferences of Eupeodes corollae (Fabricius) and Episyrphus balteatus (De Geer) were analyzed in olive groves and surrounding herbaceous and woody patches in the autumns of 2012 and 2013 in northeastern Portugal. The guts were dissected, and the pollen types were identified and compared with the ground cover plants in the studied patches. Both species consumed and selected pollen types from herbaceous and woody vegetation that occurred in different patches, indicating that they flew between patches. These results highlight the importance of conserving heterogeneous agricultural landscapes to guarantee the existence of food resources for beneficial insects during periods of scarcity.