Nocturnal Vision and Landmark Orientation in a Tropical Halictid Bee

Abstract

Despite the scarcity of photons, Megalopta is able to visually orient to landmarks at night in a dark forest understory, an ability permitted by unusually sensitive apposition eyes and neural photon summation.

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

“…However, since the x p of the DRA is not different from x = 41 ± 8 ms (n = 6 cells) measured in the frontal eye region (Fig. 4b in Warrant et al 2004) a functional significance of the higher temporal resolution in the dorsal eye region bordering the DRA is unlikely.…”

“…clouds, canopy) (Labhart 1999). This signal-to-noise ratio might be further enhanced by the significantly lower temporal resolution of Megalopta's photoreceptors compared to those of the worker honeybee (x = 27 ± 2 ms, n = 5 cells; Warrant et al 2004). The rhabdoms of the approximately 120 specialised ommatidia contain nine long rhabdomeres each, packed with parallel microvilli throughout the length of the rhabdom.…”

Ocellar optics in nocturnal and diurnal bees and wasps

“…Long before the first experimental studies of ocellar function were undertaken, these enlarged ocelli were assumed to be the main organs of vision in nocturnal Hymenoptera, with the compound eyes being merely used for daylight vision (Rau, 1933). Whilst we now know that the compound eyes are certainly used for nocturnal orientation in bees (Warrant et al, 2004), and probably also in wasps (Greiner, 2006), the enlarged ocelli of nocturnal hymenopterans still suggest they play an important role in vision at night. Exactly what role (or roles) is still a matter of conjecture, but the results presented here offer several hypotheses for future investigation.…”

“…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).…”

“…The apposition eyes of the nocturnal sweat bee Megalopta genalis, an insect capable of learning visual landmarks at starlight intensities, have thus generated considerable interest. However, despite being 30 times more sensitive to light than those of diurnal bees (Greiner et al, 2004a;Warrant et al, 2004), Megaloptds apposition eyes are still insufficiently sensitive on their own to explain the bee's impressive nocturnal visual abilities. Recent work has shown that nocturnal vision in Megalopta can be explained if neural summation of visual signals in space and time occurs at a higher level in the visual system, a hypothesis that is supported by anatomical and theoretical evidence (Greiner et al, 2004b(Greiner et al, , 2005Theobald et al, 2006).…”