The Sun is the most reliable celestial cue for orientation available to daytime migratory insects. New research led by the University of Exeter shows that small wasp look-alikes called hoverflies use a combination of the Sun and their body clock to navigate when they fly south for the winter; they keep the Sun on their left in the morning, then gradually adjust to maintain a southward route as the day goes on. The findings appear in the Proceedings of the Royal Society B.
The pied hoverfly (Scaeva pyrastri). Image credit: Will Hawkes.
“Simply flying towards the sun would lead them south, but this would create a winding, inefficient route,” said first author Dr. Richard Massy, a researcher in the Centre for Ecology and Conservation at the University of Exeter.
“Our study shows that hoverflies account for the Sun’s movement using their circadian rhythm.”
“Other animals, including certain birds and butterflies, are known to have this ability. Our work suggests that it has independently evolved across multiple insects.”
To investigate whether hoverflies use a time-compensated sun compass to orientate, the researchers undertook a series of tethered flight experiments on actively migrating pied hoverflies (Scaeva pyrastri) and yellow-clubbed hoverflies (Scaeva selenitica), caught at ground level during their southward journey over the Pyrenees.
The insects were placed in a ‘flight simulator,’ which held them in place but allowed them to swivel freely.
The hoverflies could see the Sun but not the ground (meaning they could not navigate using landmarks) and the results showed they headed south by adjusting their course based on the Sun’s position and the time of day.
This was further tested by placing some hoverflies in an artificial lighting environment for several days to shift their body clocks, then testing their navigation.
With their circadian rhythm disrupted, their direction of flight shifted westward — supporting the conclusion that they navigate using a time-compensated sun compass.
“Understanding how these insects navigate can help us predict their movements,” said senior author Dr. Karl Wotton, also from the Centre for Ecology and Conservation at the University of Exeter.
“This could be useful for conservation measures, such as limiting the use of pesticides at key migration times.”
“Hoverflies are also important predators of crop pests such as aphids, so understanding their migrations could help us use them as natural pest controllers.”
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Massy Richard et al. 2021. Hoverflies use a time-compensated sun compass to orientate during autumn migration. Proc. R. Soc. B 288 (1959): 20211805; doi: 10.1098/rspb.2021.1805
