Dorsal Ocelli Research Articles

Fine structure of the dorsal ocellus of the worker honeybee.

AbstractThe three dorsal ocelli of worker honeybees have been studied by light and electron microscopy. Each ocellus has a single flattened spheroidal lens and about 800 elongated retinular cells. Retinular cells are paired and form a two‐part plate‐like rhabdom between their distal processes. Each rhabdomere comprises parallel microvilli projecting laterally from the apposed retinular cells. Primary receptor cell axons synapse within the ocellus with ocellar nerve fibers of two different calibers. Each ocellus has eight thick fibers ca 10 m̈m in diameter and several thinner ones less than 3 m̈m in diameter. Fine structural evidence suggests that retinular axons end presynaptically on both types of ocellar nerve fibers. Since all retinular cells apparently synapse repeatedly with the thick fibers this involves a convergence of about 100:1. Thick fibers always terminate postsynaptically within the ocellus while thin fibers terminate presynaptically on other thin fibers, thick fibers or retinular axons. Structural evidence for synaptic polarization indicates that retinular cells and thick fibers are afferent, thin fibers efferent. Thus complex processing of the ocellar visual input can occur before the secondary neurons of the three ocelli converge to form the single short ocellar nerve which runs to the posterior forebrain.

Bumblebee Ocelli and Navigation at Dusk

Western bumblebees fly straight while homing by polarized light, but zigzag when they use landmarks. That flight difference was used to determine the roles of the dorsal ocelli and parts of the compound eyes in homing. Polarized light and ocelli can prolong foraging at twilight, when landmarks are no longer visible.

External Ocelli in Lepidoptera Previously Considered to be Anocellate

DORSAL ocelli are simple photoreceptors found in nymphal and adult hemimetabolous insects and adult holometabolous insects1,2. They were thought to have a variable distribution, and to be absent in many representatives of several insect orders ; in Lepidoptera several families have been considered to be entirely or partially anocellate2–4. In sphingids it has been reported that their large superposition eyes have assumed the function of the ocelli4, but it is now known that the sphingids are not anocellate. Ocelli were described within the dorsal protocerebrum in the adult of Sphinx convoluvi by Berlese5 and recently internal ocelli have been reported in several adult sphingids, saturniids and citheroniids6. There have been no descriptions of external ocelli in sphingids, saturniids, citheroniids, or any Ropalocera7.

Phototaxis in Limulus Under Natural Conditions: Evidence For Reception of Near-Ultraviolet Light in the Median Dorsal Ocellus

ABSTRACT Phototactic behaviour in Limulus mediated by lateral eye and dorsal ocellus was studied under full-spectrum and restricted-spectrum (near-u.v. and visible light) sunlight on a beach. All eyes (lateral eyes, dorsal ocelli) were occluded excepting one, which mediated the response. It was found that either a lateral eye or a dorsal ocellus alone could mediate positive phototaxis in adult Limulus under full-spectrum sunlight. When the sunlight stimulating the dorsal ocellus was filtered into restricted wavelengths, the near-u.v., but not the visible light, elicited positive phototaxis.

Spectral sensitivity studies on the visual system of the praying mantis, Tenodera sinensis.

In these studies a constant ERG response was used as a measure of visual sensitivity to different wavelengths of light. The dark-adapted compound eye of Tenodera sinensis is dominated by a single class of photoreceptors. with a major peak of sensitivity at about 510-520 nm, and with a minor peak of sensitivity in the near-ultraviolet region at about 370 nm. The dark-adapted dorsal ocellus does not contain a homogeneous population of sensory receptors. The sensitivity function of the dark-adapted ocellus to longer wavelength light (yellow and red) is determined by a single receptor with a major peak of sensitivity in the green at 510-520 nm with some sensitivity in the near-ultraviolet. Sensitivity at shorter wavelengths (near-ultraviolet and blue), however, involves the stimulation of both this and a near-ultraviolet-sensitive receptor with a maximum sensitivity at about 370 nm. Anatomically, the sensory cells of the dorsal ocellus of Tenodera were determined histologically to be grouped into two distinct regions, each group making its own separate contribution to the ocellar nerve. This may represent the separation of two different photoreceptor types in the ocellus of the mantis.

The Fine Structure of the Dorsal Ocellus of the Fleshfly

The Fine Structure of the Dorsal Ocellus of the Fleshfly

Photoinhibitory Function of the Dorsal Ocelli in the Phototactic Reaction of the Migratory Locust Locusta migratoria L.

AT least two physiological functions have been ascribed to the dorsal ocelli of locusts and insects in general. First, in response to light intensity they regulate the speed of movement (photokinesis)1 and the threshold for the initiation of certain activities2; and second, coupled with the complex eyes, they are in some unknown way involved in angular orientation, both in the phototactic1,3,4 and in the dorsal light reaction5,6.

The phototactic push-pull-coupling between dorsal ocelli and compound eyes in the phototropotaxis of locusts and crickets (Saltatoptera: Locusta migratoria and Gryllus bimaculatus)

1. Bei einem Typ der Phototropotaxis, der umgekehrt proportionalen Prophototaxis (Jander, 1963), kontrollieren die Stirnocellen von Locusta migratoria und Gryllus bimaculatus photoinhibitorisch die Starke der phototaktischen Dreherregung. 2. Die Afferenzen der Stirnocellen und der Komplexaugen von Springheuschrecken (Saltatoptera) sind bei der positiven und negativen Phototropotaxis nach dem Prinzip der phototaktischen Gegenkopplung miteinander verknupft: Bei schwacher Beleuchtung greifen die Stirnocellen als Synergisten der Komplexaugen und bei starker als Antagonisten der Komplexaugen in den Regelkreis der Tropotaxis ein. 3. Die Grille Gryllus bimaculatus percipiert mit ihren beiden lateralen Stirnocellen ahnlich wie mit den beiden Komplexaugen nach dem Prinzip der Tropotaxis die vorherrschende Lichtrichtung. Diese tropotaktischen Richtungsmeldungen der Lateralocellen und der Komplexaugen werden bei Verdunkeln des Medianocellus synergistisch und bei seiner Belichtung antagonistisch zusammengeschaltet. 4. Durch das Prinzip der phototaktischen Gegenkopplung wird die Phototropotaxis gegenuber Storungen durch Helligkeitsschwankungen stabilisiert.

Dorsal Light Receptors

THE dorsal ocelli of adult insects are present in some representatives of almost all orders except Collembola and Ephemeroptera1. Despite their wide occurrence among orders of insects, most hypotheses of their function have usually been ad hoc (for summaries of theories, see refs. 2–4). The physiological nature of the organs, their diversity throughout thousands of species, and their complex role in the integration of behaviour have not yet been thoroughly explored. Knowledge about these organs has begun to accumulate, and recent behavioural works on bees5,6 and on wasps7 give rise to the possibility that the ocelli may be associated more closely with visual perception than was previously thought. This communication is a preliminary report of the possibility that the ocelli act as visual sensitivity adjusters.

The Components of the Visual System of a Dragonfly

In this study of the electroretinograms of dragonflies (adults and nymphs) the objectives were to determine the number of classes of photoreceptors present in the visual system and to allocate these to particular morphological regions. There are probably five classes of photoreceptors present with peak sensitivities near 550, 530, 518, 420, and < 380 mmicro. The dorsal ocelli contain two classes (518 mmicro and < 380 mmicro). The ventral (anterior) ommatidia of the adult compound eye contain at least two classes (near 518 mmicro and < 380 mmicro) and probably a third class (near 550 mmicro). The dorsal ommatidia of the adult compound eye contain one class (420 mmicro) and possibly another class (< 380 mmicro). The compound eye of the nymph contains one class (530 mmicro) and possibly another class (420 mmicro).

The structure of the insect dorsal ocellus. I. General organization of the ocellus in dragonflies

The structure of the insect dorsal ocellus. I. General organization of the ocellus in dragonflies

The fine structure of a nauplius eye

The nauplius eye of the cyclopoid copepod Macrocyclops albidus has been studied by means of the electron microscope. It is composed of 1 ventral and 2 dorsal ocelli. Each dorsal ocellus consists of a large, pigmented cell, 2 tapetal cells which form a hemispherical cup and are tightly packed with crystals, 9 retinula cells and 5 conjunctival cells. The retinula cells have large masses of endoplasmic reticulum, which can be found in two distinct distributional states, also numerous bodies composed of variously coiled membranes, large amounts of glycogen, mitochondria and scattered neurotubules. The light-sensitive brush borders of these cells are closely coapted and form the irregularly shaped rhabdome. Each of the 9 retinula cells sends an axon by one of three routes to the protocerebrum. In addition, a dendrite emerges from the protocerebrum, enters the ocellus and ends blindly in immediate vicinity to the rhabdome. The observations concerning the structure of the eye made in the present study have been compared to those of light microscopical investigations. Comparison of structure and probable function of the nauplius eye and other arthropod eyes has led to consideration of the probable mode of synaptic transmission between primary and secondary sensory neurons in the ocellus, i.e. between retinula cells and eccentric cell dendrite, and various morphological features that might be of importance in this connection.

Electrophysiology of the insect dorsal ocellus. I. Origin of the components of the electroretinogram.

Dorsal ocelli are small cup-like organs containing a layer of photoreceptor cells, the short axons of which synapse at the base of the cup with dendritic terminals of ocellar nerve fibers. The ocellar ERG of dragonflies, recorded from the surface of the receptor cell layer and from the long lateral ocellar nerve, contains four components. Component 1 is a depolarizing sensory generator potential which originates in the distal ends of the receptor cells and evokes component 2. Component 2 is believed to be a depolarizing response of the receptor axons. It evokes a hyperpolarizing postsynaptic potential, component 3, which originates in the dendritic terminals of the ocellar nerve fibers. Ocellar nerve fibers in dragonflies are spontaneously active, discharging afferent nerve impulses (component 4) in the dark-adapted state. Component 3 inhibits this discharge. The ERG of the cockroach ocellus is similar. The main differences are that component 3 is not as conspicuous as in the dragonflies and that in most cases ocellar nerve impulses appear only as a brief burst at "off." In one preparation a spontaneous discharge of nerve impulses was observed. As in the dragonflies, this was inhibited by illumination.

A comparison of the electrical responses of compound eyes and dorsal ocelli in four insect species

Electroretinograms (e.r.g.s) of compound eyes and dorsal ocelli in three diurnal insects— Apis mellifera, Pachydiplax longipennis, and Phormia regina—have high flicker fusion frequencies in the range 190/sec to 350/sec. The e.r.g.s of compound eye and ocellus in one nocturnal insect, Periplaneta americana, have flicker fusion frequencies in the range 45/sec to 60/sec. Flicker data for the compound eyes confirm to the earlier observations of Autrum (1950). Autrum's suggestion that fast eyes (those with high f.f.f.) may be further characterized by a typical e.r.g. wave form, low photic sensitivity and extremely rapid rate of dark adaptation lacks generality. The honeybee compound eye (f.f.f.=265/sec) has an e.r.g. quite similar in wave form to that of the cockroach compound eye (f.f.f.=60/sec). None of the eyes studied has higher sensitivity than the dragonfly ocellus, an eye which has a flicker fusion frequency of about 200/sec. This same ocellus dark-adapts no more rapidly than the cockroach compound eye. Wave form of the e.r.g., photic sensitivity, and rate of dark adaptation are independent visual functions, not necessarily related to each other or to flicker fusion frequency. The data suggest that the ability to resolve high rates of flicker depends on properties of the retinula cells themselves and not on properties of postsynaptic electrical events as suggested by Autrum (1952).

The spectral sensitivities of the dorsal ocelli of cockroaches and honeybees; an electrophysiological study.

The spectral sensitivities of the dorsal ocelli of cockroaches (Periplaneta americana, Blaberus craniifer) and worker honeybees (Apis mellifera) have been measured by electrophysiological methods. The relative numbers of quanta necessary to produce a constant size electrical response in the ocellus were measured at various wave lengths between 302 and 623 mmicro. The wave form of the electrical response (ERG) of the dark-adapted roach ocellus depends on the intensity but not the wave length of the stimulating light. The roach ocellus appears to possess a single photoreceptor type, maximally sensitive about 500 mmicro. The ERG's of bee ocelli are qualitatively different in the ultraviolet and visible regions of the spectrum. The bee ocellus has two types of photoreceptor, maximally sensitive at 490 mmicro and at about 335 to 340 mmicro. The spectral absorption of the ocellar cornea of Blaberus craniifer was measured. There is no significant absorption between 350 and 700 mmicro.

The electrical responses of dorsal ocelli in cockroaches and grasshoppers

The electroretinograms of dorsal ocelli in cockroaches and grasshoppers were recorded using extra-cellular electrodes. Different components of the electroretinograms were allocated to their sites of origin. Two slow potentials with opposite electrical sign, which sum algebraically and which may interact in an oscillatory manner, originate in the layer of photoreceptor cell bodies. Efferent nerve impulses, originating in the largest of the ocellar nerve fibres, appear on darkening the ocellus.

Electrical responses of insect dorsal ocelli.

Electrical responses of insect dorsal ocelli.

The Functions of the Eyes and Antennae in the Orientation of Adults of Neodiprion lecontei (Fitch)

A recent paper (2) described the light reactions of Sarcophaga aldrichi Parker when the eyes of the fly were treated in different ways. The present paper describes a similar series of observations on adults of the sawfly, Neodiprion lecontei (Fitch), and analyses the functions of their compound eyes, dorsal ocelli, and antennae.