Abstract
To make a smooth touchdown when landing, an insect must be able to reliably control its approach speed as well as its body and leg position—behaviors that are thought to be regulated primarily by visual information. Bumblebees forage and land under a broad range of light intensities and while their behavior during the final moments of landing has been described in detail in bright light, little is known about how this is affected by decreasing light intensity. Here, we investigate this by characterizing the performance of bumblebees, B. terrestris, landing on a flat platform at two different orientations (horizontal and vertical) and at four different light intensities (ranging from 600 lx down to 19 lx). As light intensity decreased, the bees modified their body position and the distance at which they extended their legs, suggesting that the control of landing in these insects is visually mediated. Nevertheless, the effect of light intensity was small and the landings were still well controlled, even in the dimmest light. We suggest that the changes in landing behavior that occurred in dim light might represent adaptations that allow the bees to perform smooth landings across the broad range of light intensities at which they are active.
Highlights
To ensure a safe and smooth landing, a flying insect has to regulate its speed, modify its body posture and extend its legs in good time before making contact with the surface
To investigate the ability of the landing bees to assess the distance to the platform in dim light, we examined the distance between the bee and the platform during the hover phase at two different platform orientations (0◦ and 90◦) and at four different light levels (19, 60, 190 and 600 lx)
We have shown that light intensity has an effect on the timing of leg extension and the body posture of bumblebees landing on a flat platform at two different orientations (0◦ and 90◦ relative to the horizontal plane) and at four different light intensities
Summary
To ensure a safe and smooth landing, a flying insect has to regulate its speed, modify its body posture and extend its legs in good time before making contact with the surface. This task becomes more challenging because contrast discrimination becomes increasingly difficult. This is, in part, due to the low number of photons that are available and the fact that they arrive at the retina in a random and unpredictable way (Warrant and McIntyre, 1993). This random arrival of photons causes visual ‘‘noise’’ that degrades the reliability of vision (Rose, 1942; De Vries, 1943). Transducer noise (Lillywhite, 1977, 1981; Lillywhite and Laughlin, 1979; Laughlin and Lillywhite, 1982) and dark noise (Barlow, 1956) further add to the unreliability of vision at low light levels
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