Understanding the winter biology of beneficial insects such as hover flies (family Syrphidae) is an understudied, yet vastly important area of research. Insects including butterflies, dragonflies, and moths migrate hundreds of miles south in response to encroaching winter conditions, but little research has investigated this behavior outside of these taxa. Indeed, radar studies reveal massive seasonal bioflows of insects at a continental scale. In Europe, it is known that hover flies are among the taxa that move these extraordinary distances, but no studies to date have investigated this behavior in North American species. The purpose of this project, therefore, was to reveal the presence or absence of a fall migratory strategy in Midwestern hover fly species by examining stable deuterium isotopes found within fixed tissues. Stable deuterium isotopes (δ2H) fluctuate predictably on a north-south gradient throughout North America and can be used as natural markers to determine natal origins of insects. Therefore, by sampling common hover fly species from July-October in Urbana, IL, we sought to determine whether any individuals exhibited non-local isotopic signatures indicative of a migratory event.
Results/Conclusions
Our isotope results suggest that two common aphidophagous Midwestern hover fly species migrate south during autumn. Based on established isotope maps, we infer that the more negative the δ2H values, the further north an insect developed. We determined that local central Illinois δ2H values within hover fly wing and leg chitin reliably range between -90 and -130 δ2H and that certain individuals of both Eupeodes americanus and Syrphus ribesii collected during autumn exhibit substantially negative δ2H values outside of this range. Eupeodes americanus displayed the most dramatic pattern, with most individuals during late August and early/middle September exhibiting δ2H values between -140 δ2H and -181 δ2H, while those collected during July and late September/early October exhibited local signatures. The third species, Allograpta obliqua exhibited local signatures throughout the season with little to no pattern suggestive of a migration. The adult stages of most hover fly species are important pollinators of a variety of crops, while the larvae occupy a wide array of niches from detritivores to aphidophagous predators. Therefore, these data have major implications for several fields including pollination ecology, integrated pest management, and conservation biology.