A behavioural investigation into Eristalis tenax : Pursuit, approach estimation, locomotor activity and rearing

Abstract: Hoverflies are suggested to be the 2nd most important pollinator group after bees and bumblebees, and with the changing climate and dwindling numbers of pollinators it might never have been more important understanding our pollinators. Given the hoverflies’ small brains, beautiful aerial acrobatics, good temporal resolution, but limited spatial resolution, these flies make interesting study animals for flight behaviour and vision research. Eristalis tenax hoverflies are globally spread generalist pollinators, thus well suited for studies internationally. However, due to weather and behavioural seasonality, the hoverflies can be hard to access all year round. Furthermore, only observational studies have been performed to investigate their activity rhythm, and neither pursuit behaviour nor interactions with other insects are well studied. We therefore developed a new protocol for rearing E. tenax, and by adding artificial hibernation we managed to get the hoverflies to survive up to a year – making the hoverflies accessible all year round. Using LAMS, we confirmed earlier suggestions that E. tenax are diurnal, and also showed that they are active during the entire light phase of an LD cycle. We also found that the hoverflies locomotor activity is remarkably robust – it was not affected by age, diet or starvation. However, an accompanying conspecific did affect the locomotor activity. Using high speed videography in the field we found that female Eristalis are affected by the presence of other insects outdoors as well. The females escaped their food flowers 94 % of the times they were approached, even though only 16 % of the incomers were potentially dangerous wasps. Interestingly, the females seemed to be able to distinguish between wasps and other incomers, leaving the flowers earlier and at a higher speed when approached by wasps. Bringing our high-speed cameras indoors we developed a flight arena, allowing for studies of eristaline flight behaviour all year round. Using this setup, we found that male E. tenax pursue beads 6 - 38.5 mm in diameter traveling at 0 - 1.8 ms-1. Fascinatingly, we found that the flies pursued the beads from both below and above, often keeping the target outside their bright zone.