Navigation and flight capabilities of migratory hoverflies

Abstract

Many insects undergo spectacular long-distance migrations to profit from ephemeral resources and escape punishing winters. This project aims to elucidate the mechanisms and adaptations that permit long-distance migration and introduces hoverflies as model organisms in the study of migratory behaviour. Episyrphus balteatus and Scaeva spp. hoverflies are partial migrants, where a subset of the population migrates, which varies with latitude. They are shown to use the sun to navigate during their southward autumn migration, compensating for its changing position in the sky, an ancestral mechanism that could be present in the brains of many insects. The level of compensation was found to be less than expected, although modelling the efficiency of the southward components of simulated vectors revealed that even partial compensation can be incredibly efficient. Hoverflies may thus partially compensate, allowing them to disperse over a wider area during their southward migration. Migrating hoverfly morphs were shown to fly longer and further, but not faster, than non-migrating morphs , which allows them to undertake long migrations efficiently. The distance travelled also varied by body condition, where hoverflies with fat abdomens flew further than those with medium or thin abdomens. This difference was less pronounced in autumn hoverflies suggesting that thin and medium autumn migrants are more motivated to fly than their summer non-migratory counterparts. Together, these studies cover the different traits that underpin migration. By directly sampling migrating and non-migrating hoverflies, the migratory adaptations have been outlined as clearly as possible. This thesis establishes the groundwork of a new study system that can be built upon with further research.