The last meal of an Eocene pollen-feeding fly

Abstract

One of the most important trophic interactions today is that between insects and their floral hosts. This biotic association is believed to have been critical to the radiation of flowering plants and many pollinating insect lineages over the last 120 million years (Ma). Trophic interactions among fossil organisms are challenging to study, and most inferences are based on indirect evidence. Fossil records providing direct evidence for pollen feeding, i.e., fossil stomach and gut contents, are exceptionally rare.1,2 Such records have the potential to provide information on aspects of animal behavior and ecology as well as plant-animal interactions that are sometimes not yet recognized for their extant relatives. The dietary preferences of short-proboscid nemestrinids are unknown, and pollinivory has not been recorded for extant Nemestrinidae.3 We analyzed the contents of the conspicuously swollen abdomen of an ca. 47.5 Ma old nemestrinid fly of the genus Hirmoneura from Messel, Germany, with photogrammetry and state-of-the-art palynological methods. The fly fed on pollen from at least four plant families-Lythraceae, Vitaceae, Sapotaceae, and Oleaceae-and presumably pollinated flowers of two extant genera, Decodon and Parthenocissus. We interpret the feeding and foraging behavior of the fly, reconstruct its preferred habitat, and conclude about its pollination role and importance in paratropical environments. This represents the first evidence that short-proboscid nemestrinid flies fed, and possibly feed to this day, on pollen, demonstrating how fossils can provide vital information on the behavior of insects and their ecological relationships with plants.