Insights into natal origins of migratory Nearctic hover flies (Diptera: Syrphidae): New evidence from stable isotope (δ2H) assignment analyses

<p>Hover flies (Diptera: Syrphidae) are an important group of insects that provide a multitude of key ecosystem services including pollination and biological control, yet many of their major life history traits are not understood. Some Palearctic hover fly species are known to migrate in response to changing seasonal conditions, yet this behavior is almost entirely unrecognized in Nearctic species. At least one species, <em>Eupeodes</em> <em>americanus</em> (Wiedemann 1830), is partially migratory during autumn while <em>Allograpta</em> <em>obliqua</em> may be non-migratory, but it is unknown where these insects originate and how far they may travel. We examined natal origins of two Nearctic hover fly species, <em>Allograpta</em> <em>obliqua</em> and <em>Eupeodes</em> <em>americanus</em>, using stable hydrogen isotope (δ²H) measurements of metabolically inactive tissues (wings and legs) to derive a hover fly δ²H isoscape. While <em>Allograpta</em> <em>obliqua</em> was mostly of local origin, several <em>Eupeodes</em> <em>americanus</em> were sourced from northern latitudes in the Midwestern United States and Canada, representing travel distances of up to 3,000 km likely using seasonally favorable air currents. This phenomenon is expected to have major ecological and economic ramifications, especially in the realm of plant pollination ecology and biological control.</p>