Visual ecology of Indian carpenter bees I: Light intensities and flight activity

Abstract

Bees are mostly active during the daytime, but nocturnality has been reported in some bee families. We studied temporal flight activity in three species of carpenter bees (genus Xylocopa) in relation to light intensities. X. leucothorax is diurnal, X. tenuiscapa is largely diurnal being only occasionally crepuscular, while X. tranquebarica is truly nocturnal. Occasional forays into dim light by X. tenuiscapa are likely to be due to the availability of richly rewarding Heterophragma quadriloculare (Bignoniaceae) flowers, which open at night. X. tranquebarica can fly even during the moonless parts of nights when light intensities were lower than 10(-5) cd m(-2), which makes this species the only truly nocturnal bee known so far. Other known dim-light species fly during crepuscular or moonlit periods. We compare eye and body sizes with other known diurnal and dim-light bees. We conclude that while extremely large ocellar diameters, large eye size:body size ratio, large number of ommatidia and large ommatidial diameters are all adaptations to dim-light foraging, these alone do not sufficiently explain the flights of X. tranquebarica in extremely dim light. We hypothesise that additional adaptations must confer extreme nocturnality in X. tranquebarica.

Cockroach optomotor responses below single photon level

“…The mean light intensity in the VR setup we used is even lower, attributable to the 50% black and 50% white stimulus grating that was used. Visual behaviour may be possible at even lower average intensities, as shown in studies with nocturnal bees foraging in their natural habitats: Xylocopa tranquebarica at 10 −5 cd m −2 (Somanathan et al, 2008) (corresponding in our estimation to ~6.3×10 −5 lx) and Megalopta genalis at 10 −4 cd m −2 ) (corresponding to ~6.3×10 −4 lx); and foraging toads in the laboratory settings at 10 −5 lx (Aho et al, 1988). However, natural forest environments and the experimental setup used by Aho et al (Aho et al, 1988) probably contain higher local contrasts than the 0.33 that is attainable in the VR, possibly making movement detection more challenging in the latter (Heimonen et al, 2012;O'Carroll et al, 2012).…”

Light and dark adaptation mechanisms in the compound eyes of Myrmecia ants that occupy discrete temporal niches

“…Nilsson, 1989Nilsson, , 1990) -typically limits vision to bright daylight conditions because each photoreceptor receives light through one small facet lens only (Greiner, 2006;Schwarz et al, 2011;Warrant et al, 2004). However, several hymenopteran insects are active in dim light conditions (Greiner, 2006;Greiner et al, 2007;Kelber et al, 2006Kelber et al, , 2003Klotz and Reid, 1993;Narendra et al, 2010;Somanathan et al, 2008Somanathan et al, , 2009Wolda and Roubik, 1986) and have modified apposition compound eyes to increase photon capture: larger lenses, wider and longer rhabdoms and spatial and temporal pooling of photoreceptor signals across neighbouring ommatidia (Stöckl et al, 2016;Warrant and Dacke, 2011). Such highly sensitive eyes have then to be protected against bright light.…”

Resolution and sensitivity of the eyes of the Asian honeybees Apis florea, Apis cerana and Apis dorsata

“…Crepuscular or nocturnal foraging activity -requiring flight in rather dim light -has been reported from several genera in four families of the Apoidea (for a review, see Kelber et al, 2006), ranging from the minute Perdita bequaertiana to the large Xylocopa tranquebarica (Burgett and Sukumalanand, 2000;Somanathan et al, 2008). These bees, like all bees, possess apposition compound eyes.…”

“…These bees, like all bees, possess apposition compound eyes. The transition to a dim-light environment is an apparent disadvantage to animals with apposition eyes because these eyes tend to have a very low absolute sensitivity, due to the small diameter of their facet lenses (see Warrant et al, 2004;Kelber et al, 2006;Somanathan et al, 2008). However, several reasons may have made this transition to a dim-light environment favourable for at least some species (see Wcislo et al, 2004).…”

“…The only species of bee known to fly all night is the Indian carpenter bee X. tranquebarica, which seems to avoid competition (Somanathan and Borges, 2001;Somanathan et al, 2008). The latter facultatively nocturnal species, however, has also been found to collect pollen from a nocturnally flowering tree, Heterophragma quadriloculare, and is able to fly in dim light to do so.…”