Flight control and landing precision in the nocturnal bee Megalopta is robust to large changes in light intensity

Abstract

Like their diurnal relatives, Megalopta genalis use visual information to control flight. Unlike their diurnal relatives, however, they do this at extremely low light intensities. Although Megalopta has developed optical specializations to increase visual sensitivity, theoretical studies suggest that this enhanced sensitivity does not enable them to capture enough light to use visual information to reliably control flight in the rainforest at night. It has been proposed that Megalopta gain extra sensitivity by summing visual information over time. While enhancing the reliability of vision, this strategy would decrease the accuracy with which they can detect image motion—a crucial cue for flight control. Here, we test this temporal summation hypothesis by investigating how Megalopta's flight control and landing precision is affected by light intensity and compare our findings with the results of similar experiments performed on the diurnal bumblebee Bombus terrestris, to explore the extent to which Megalopta's adaptations to dim light affect their precision. We find that, unlike Bombus, light intensity does not affect flight and landing precision in Megalopta. Overall, we find little evidence that Megalopta uses a temporal summation strategy in dim light, while we find strong support for the use of this strategy in Bombus.

The remarkable visual capacities of nocturnal insects: vision at the limits with small eyes and tiny brains

“…Despite having tiny eyes and small brains, nocturnal insects have remarkable visual abilities in dim light, performing sophisticated visual behaviours when the photoreceptors each absorb only a weak trickle of photons. Nocturnal insects can see colour [33,39], control flight and land [59,60], react to faint movements in their environment [4], navigate using dim celestial cues [40,41,[61][62][63] and find their way home after a long and tortuous foraging trip using learned visual landmarks [3,32,35,36,89]. Part of this ability lies in the optical designs of their sensitive compound eyes which maximize light capture.…”

“…At night, through a perishingly dark and tangled rainforest, the nocturnal bee Megalopta is able to recall learned visual landmarks to find its way home to its small and inconspicuous nest when fewer than five photons are being absorbed by each of its photoreceptors per second [3]. At the same light levels, this bee also uses optic flow cues to control its flight [59] and to land on its nest with an ease and precision no different to that of a diurnal bee in bright light [60]. Even though their photon absorption rates have yet to be measured, the conclusion is likely to be the same for many other nocturnal insects.…”

The impact of artificial light at night on nocturnal insects: A review and synthesis

“…Moths and some nocturnal beetles have evolved superposition eyes with rhabdoms that collect light from multiple facets, sacrificing resolution to gain up to 1,000× more sensitivity than apposition eyes of similar dimension (Cronin et al, ; Horridge, ). Some crepuscular bees, ants, and dung beetles have more recently transitioned to a nocturnal niche, and possess apposition eyes with larger lenses and wider rhabdoms that sum photons over time and/or space to increase sensitivity (Baird, Fernandez, Wcislo, & Warrant, ; Warrant & Dacke, ). Among dung beetles, larger eye size, smoother facets, and absence of screening pigment correlate to nocturnal activity (McIntyre & Caveney, ).…”

Comparative system identification of flower tracking performance in three hawkmoth species reveals adaptations for dim light vision

“…Bumblebees as well as hornets reduce their flight speed with decreased light intensity, which has been suggested as a mechanism to cope with the reduced temporal acuity of the visual system caused by temporal summation [22,24]. In contrast, nocturnal sweat bees do not change their flight speed during landing [23] or tunnel flight [25], and spatial summation has been suggested to underlay their high sensitivity at night. While qualitative similarities and species-specific differences are emerging, we do not yet understand from a quantitative, much less a mechanistic, standpoint how the physiological adaptations for low-light vision translate to behaviour differences across species.…”