Light wavelength and intensity modulate phototaxis in the nocturnal bee Megalopta aegis

Positive phototaxis in diurnal bees is modulated by wavelength and intensity of light. Unlike diurnal bees, nocturnal bees like Megalopta aegis forage exclusively during twilight, when light intensity drops rapidly and irradiance peaks in the blue spectrum. How light parameters influence phototaxis in these nocturnal bees remains unclear. We evaluated the phototactic responses of M. aegis in a dark circular arena using UV, blue, and green monochromatic lights presented at six absolute intensities. Contrary to diurnal bees, M. aegis was not always attracted to light. When attracted, they showed stronger attraction to UV than to blue or green. Paths toward UV were shorter, faster, and straighter, suggesting a greater involvement of UV-photoreceptors in this phototactic behaviour. Compared to honeybees tested in similar experimental setups, M. aegis exhibited slower but more directed paths. These results align with their highly light-sensitive eyes, which trade-off temporal resolution for improved reliability in dim light.