Hornets Can Fly at Night without Obvious Adaptations of Eyes and Ocelli

Abstract

Hornets, the largest social wasps, have a reputation of being facultatively nocturnal. Here we confirm flight activity of hornet workers in dim twilight. We studied the eyes and ocelli of European hornets (Vespa crabro) and common wasps (Vespula vulgaris) with the goal to find the optical and anatomical adaptations that enable them to fly in dim light. Adaptations described for obligately nocturnal hymenoptera such as the bees Xylocopa tranquebarica and Megalopta genalis and the wasp Apoica pallens include large ocelli and compound eyes with wide rhabdoms and large facet lenses. Interestingly, we did not find any such adaptations in hornet eyes or ocelli. On the contrary, their eyes are even less sensitive than those of the obligately diurnal common wasps. Therefore we conclude that hornets, like several facultatively nocturnal bee species such as Apis mellifera adansonii, A. dorsata and X. tenuiscapa are capable of seeing in dim light simply due to the large body and thus eye size. We propose that neural pooling strategies and behavioural adaptations precede anatomical adaptations in the eyes and ocelli when insects with apposition compound eyes turn to dim light activity.

Activity rhythm and action range of workers of the invasive hornet predator of honeybees Vespa velutina, measured by radio frequency identification tags

“…First, most of the activity is realized between 07:00 a.m. and 08:00 p.m., confirming that V. velutina is diurnal; some individuals still have a nocturnal activity (only 2% of the activity). V. crabro is also active with low light intensity but in a higher propensity (Kelber et al., 2011). Second, the worker activity is driven by weather conditions that is quite classical in Vespidae (Canevazzi & Noll, 2011; de Castro, Guimaraes, & Prezoto, 2011; Cruz, Giannotti, Santos, Bichara Filho, & Resende, 2006; Kasper, Reeson, Mackay, & Austin, 2008; da Rocha & Giannotti, 2007).…”

Visual Adaptations for Mate Detection in the Male Carpenter Bee Xylocopa tenuiscapa

“…Briefly described here are the standard procedures that were followed to map interommatidial angles in the frontal part of the visual field [21, 46, 47]. An immobilised bee was mounted at the centre of curvature of a Leitz goniometer with the flat posterior eye edge parallel to the plane of the goniometer stage, and placed beneath an optical apparatus consisting of a Canon MD150 digital video camcorder and an inverted Hasselblad Distagon 1:3.5 60 mm camera objective (with 80 mm back focal distance).…”

Brain Size and Visual Environment Predict Species Differences in Paper Wasp Sensory Processing Brain Regions (Hymenoptera: Vespidae, Polistinae)

“…The evolution of nocturnality in flying Hymenoptera (bees and wasps) is associated with changes in compound eye structure: eye size (number of facets), light-gathering lens size, and/or the size of light receptive surfaces increase compared to diurnal relatives [Warrant et al, 2004;Greiner, 2006;Warrant, 2008]. However, these changes are not sufficient to maintain visual acuity under the eight-order-of-magnitude-lower light levels experienced during night flight, and neural processing such as summation of light inputs across eye facets may be necessary to permit nocturnal foraging [Greiner, 2006;Warrant, 2008;Kelber et al, 2011]. Our data suggest that, as in nocturnal vertebrates, the relative reliance on olfaction increases even when anatomical adaptations for low-light visual acuity arise.…”