Light intensity limits foraging activity in nocturnal and crepuscular bees

Anatomical and physiological evidence for polarisation vision in the nocturnal bee Megalopta genalis

“…Thus, with the high polarisation sensitivity present in the DRA of the nocturnal bee M. genalis, the polarisation pattern during this twilight period represents a simple and reliable orientation cue. Indeed, the onset and offset of Megalopta's activity periods correlate well with the beginning and end of astronomical twilight (Kelber et al 2006). However, since the orientations of the ommatidia of the DRA and their visual overlaps with neighbouring ommatidia could not be measured, we do not yet know how this array of analysers exploits the simple e-vector pattern of twilight.…”

“…On the other hand, its light intensity is low, and orienting at such times requires a highly sensitive polarised light detector. The halictid bee M. genalis forages exclusively during twilight, where one foraging trip is typically made in the evening, and between one and four trips in the morning (Kelber et al 2006). Interestingly, the onset of morning foraging correlates well with (and never occurs before) the beginning of astronomical twilight in the morning, while evening foraging finishes at least 25 min before the end of astronomical twilight (Kelber et al 2006).…”

“…The halictid bee M. genalis forages exclusively during twilight, where one foraging trip is typically made in the evening, and between one and four trips in the morning (Kelber et al 2006). Interestingly, the onset of morning foraging correlates well with (and never occurs before) the beginning of astronomical twilight in the morning, while evening foraging finishes at least 25 min before the end of astronomical twilight (Kelber et al 2006). Because of this correlation, we hypothesise that just as in their diurnal relatives, polarisation vision may play an important role in the long-distance homing flights of the nocturnal M. genalis.…”

Ocellar optics in nocturnal and diurnal bees and wasps

“…Overwhelming evidence from bees (Kerfoot, 1967;Kelber et al, 2006) and ants (Moser et al, 2004) shows a strong correlation between ocellar size and the light intensity at peak activity: species active in dimmer light have larger ocelli. The ocellar sizes of the nocturnal and diurnal bees and wasps presented in this paper are in accordance with this correlation (Fig.…”

“…The initiation and cessation of daily activity frequently occurs at a particular threshold light intensity (Schricker, 1965;Dreisig, 1980;Warrant et al, 2004;Kelber et al, 2006), and both bees (Schricker, 1965;Gould, 1975) and moths (Eaton et al, 1983;Sprint and Eaton, 1987) use their ocelli to measure this intensity. If the ocelli are occluded, the timing of activity is significantly altered (Eaton et al, 1983;Sprint and Eaton, 1987;Wunderer and de Kramer, 1989).…”