Electrophysiology and histology of the eye of the bumblebeeBombus hortorum(L.) (Hymenoptera: Apidae)

Abstract

Ultrastructural investigations showed that amongst all the hymenopteran eyes examined to date, those of the bumblebee and honeybee exhibit the greatest similarity. Ommatidia in both species are of the apposition type. Minor, but nonetheless noteworthy differences, include the lack of interfacetal hairs in the bumblebee, the rather smooth and flat outer corneal surface, the relatively thick cornea and the larger rhabdoms and retinula cells in the bumblebee eye. Twisting of the rhabdoms or rhabdomeres was not seen. Intracellular electrophysiological responses provided the basis for study of flicker fusion frequency and absolute, polarization, spectral and angular sensitivites. The bumblebee compound eye has a flicker fusion frequency of approximately 130 Hz. Twin flashes resulted only in two distinct responses when the light levels were low. Bright light tended to lead to a suppression of the second depolarization in a twin flash response. Beyond a certain critical brightness, visual cells can no longer simply respond with a potential increase to an increase in light intensity; instead, they react with an increase in response area and a prolonged depolarization afterpotential. Since the latter disappears when the frequency of stimulation is raised, neither the Bunsen-Roscoe law nor the Weber-Fechner response/stimulus intensity relationship can be used to fully describe this phenomenon. Three basic types of retinula cells were found electrophysiologically: II cells possessed a singular sensitivity peak in the ultraviolet (353 nm), 10 cells had a clear peak in the blue (430 nm) and a secondary one in the ultraviolet, and 54 cells exhibited greatest sensitivity in the green to light of 548 nm wavelength. Green-sensitive cells had a secondary peak in the ultraviolet. Polarization sensitive cells were found only amongst ultraviolet and blue cells, but both spectral groups also contained the same number of polarization insensitive cells. It is believed that ultraviolet, blue and green cells can all occur in the same ommatidial unit but that it is unlikely that different visual pigments are housed in the same visual cell. Electroretinogramme recordings were used to measure angular and spectral response curves of the dorsal ocellus. The eye of the bumblebee appears adapted to carry out quick angular flight manoeuvres in bright sunlight. The larger rhabdom and acceptance angle, on the other hand, must give the bumblebee an advantage over the honeybee to forage in somewhat dimmer ambient light conditions. It is concluded that bumblebees, like honeybees, make use of shapes and colours of flowers, use in navigation the polarization pattern of the sky, and that their temporal and spatial resolution allows them to retain relatively fine details of their environment.

Molecular characterization and expression of the UV opsin in bumblebees:three ommatidial subtypes in the retina and a new photoreceptor organ in the lamina

“…Physiological investigations indicated that honeybee and bumblebee ocelli have a peak sensitivity in the blue-green as well as in the UV part of the light (MeyerRochow, 1981;Ruck and Goldsmith, 1958). Meyer-Rochow (1981) estimated the UV peak sensitivity of the bumblebee median ocellus to be 353·nm, which is indistinguishable from the peak sensitivity of the UV visual pigment of the compound eye (Bernard and Stavenga, 1978). It is therefore not entirely surprising that we found UV opsin-ir rhabdomeres in all three ocelli.…”

“…[Intracellular recordings from photoreceptor cells in the Bombus hortorum compound eye confirm the presence of three types of photoreceptor with a peak sensitivity in the UV (353·nm), the blue (430·nm) and the green (548·nm); Meyer-Rochow, 1981.] However, reliable morphological characterization of the different bee receptor types is difficult due to the twist of the ommatidium around its long axis and possible (but, in most cases, neglected) morphological receptor variation in different parts of the eye (see discussion in Menzel and Blakers, 1976).…”

Effect of light intensity on flight control and temporal properties of photoreceptors in bumblebees

“…This is justified in the sense that the size of the elements in the random chequerboard pattern (2×2 cm) is seen by the photoreceptors at an angle of ∼7.5 deg, when the bees are flying near the centre of the tunnel. This angle is much larger than the receptive field of the photoreceptors (Meyer-Rochow, 1981).…”

“…Moreover, we included the effect of shot noise by estimating the number of photons (N ) arriving at a single photoreceptor within one photoreceptor integration time (Δt) with the equation: , D is the diameter of a compound eye facet and Δρ is the acceptance angle (Land, 1997). For B. terrestris, D=28 µm and Δρ=3.8 deg (Meyer-Rochow, 1981). Shot noise (√N) was calculated for the light stimulation supplied to the eye by both the white (ON) and black (OFF) squares of the tunnel at each light level.…”

The compound eye of Orgyia antiqua (Lepidoptera: Lymantriidae): Sexual dimorphism and light/dark adaptational changes

“…Day-active, flying insects generally appear to have a compound eye with high resolution like dragonflies (Laughlin & McGinness, 1978), houseflies (Laughlin & Weckström, 1993), butterflies (Rutowski & Warrant, 2002), honey-and bumblebees (Laughlin & Horridge, 1971;Meyer-Rochow, 1981) and some diurnally-active moths (Horridge et al, 1977), especially when there is a need for the insect to evade predators, visually procure food, or search for a mate by sight. As O. antiqua is a capital breeder, i.e.…”