Visual approach computation in feeding hoverflies.

Malin Thyselius,Trevor Wardill,Karin Nordström,Paloma Gonzalez-Bellido

doi:10.1242/jeb.177162

Malin Thyselius, Trevor Wardill + Show 2 more

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https://doi.org/10.1242/jeb.177162

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Abstract

ABSTRACTOn warm sunny days, female hoverflies are often observed feeding from a wide range of wild and cultivated flowers. In doing so, hoverflies serve a vital role as alternative pollinators, and are suggested to be the most important pollinators after bees and bumblebees. Unless the flower hoverflies are feeding from is large, they do not readily share the space with other insects, but instead opt to leave if another insect approaches. We used high-speed videography followed by 3D reconstruction of flight trajectories to quantify how female Eristalis hoverflies respond to approaching bees, wasps and two different hoverfly species. We found that, in 94% of the interactions, the occupant female left the flower when approached by another insect. We found that compared with spontaneous take-offs, the occupant hoverfly's escape response was performed at ∼3 times higher speed (spontaneous take-off at 0.2±0.05 m s−1 compared with 0.55±0.08 m s−1 when approached by another Eristalis). The hoverflies tended to take off upward and forward, while taking the incomer's approach angle into account. Intriguingly, we found that, when approached by wasps, the occupant Eristalis took off at a higher speed and when the wasp was further away. This suggests that feeding hoverflies may be able to distinguish these predators, demanding impressive visual capabilities. Our results, including quantification of the visual information available before occupant take-off, provide important insight into how freely behaving hoverflies perform escape responses from competitors and predators (e.g. wasps) in the wild.

Highlights

Many insects visit flowering plants, serving an important ecological role as pollinators while feeding on pollen and nectar (Gilbert, 1985; Gladis, 1997; Jauker et al, 2012; Kikuchi, 1965; Ssymank et al, 2008)
None of the flower species (Table 1) from which the female Eristalis were feeding had large corollas, and we hypothesized that when approached by other insects, the occupant hoverfly would perform an evasive maneuver (Kikuchi, 1962b, 1963)
The occupant hoverfly performs a directed take-off We investigated how female Eristalis left the flower when approached by an incoming insect, and compared this with spontaneous take-offs, i.e. those that were not induced by an incomer

Summary

Introduction

Many insects visit flowering plants, serving an important ecological role as pollinators while feeding on pollen and nectar (Gilbert, 1985; Gladis, 1997; Jauker et al, 2012; Kikuchi, 1965; Ssymank et al, 2008). The hoverfly genus Eristalis, for example, feeds from flowers during the daylight hours of spring and summer (Howarth and Edmunds, 2000; Ottenheim, 2000). Female Eristalis hoverflies are often found close to the flowers from which they feed (Gilbert, 1981, 1985), often in the presence of other insects (Golding and Edmunds, 2000; Rashed and Sherratt, 2007). Whereas some insects approaching the flower may compete for food, others, such as wasps, pose a survival risk (Akre, 1982). There is a trade-off between staying, which poses a risk of getting eaten or injured, and leaving the flower, which leads to lost feeding time and energy intake (Cooper and Frederick, 2007)

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