Enhanced flight performance in hoverfly migrants

Many animals undergo seasonal migrations in which they travel long distances aided by variations in morphology, physiology, and behavior. Here, we compare the flight characteristics, measured in a tethered flight mill, of autumn migratory and summer non-migratory morphs of the marmalade hoverfly Episyrphus balteatus (Diptera: Syrphidae), an ecologically and economically important pollinator, pest predator, and long-distance migrant. Our results show that migratory morphs flew twice as far as the non-migratory morphs. Body condition, reflecting the quantity of energy stores, had an even greater effect as hoverflies with fat abdomens flew almost five times the distance of those with thin abdomens, whereas speed varied only by size. These findings demonstrate enhanced flight capabilities in migratory morphs and underscore the importance of body condition for long-distance flight. Consequently, resource availability, feeding behavior, and the ability to accumulate and utilize fuel are likely to be key factors influencing the migration of hoverflies.