Sensilla on the maxillary palps of Helicoverpa armigera caterpillars: in search of the CO(2)-receptor

The ultrastructure of sensilla on the maxillary palps of helicoverpa armigera caterpillars has been investigated in order ot find candidates for CO(2)-receptors. The following sensilla are found on the palps: a) 8 chemosensory pegs at the tip; b), a large distal pore plate; c), a smaller proximal pore plate; d), a digitiform organ; e), a campaniform sensillum; and f), 3 scolopidia. Each chemosensory peg at the tip is innervated by 4-5 sensory neurons. Five of these pegs are most probably contact chemoreceptors, because each has a dendrite with a tubular body. The distal pore plate has a porous cuticle and is innervated by 3 sensory neurons, each of which sends a highly branched dendrite into a large cuticular cavity. The proximal pore plate is made up from two fused organs, has also a porous cuticle, and is innervated by two sensory neurons which send their dendrites into a narrow cuticular channel. The digitiform organ is innervated by one sensory cell which sends a highly lamellated dendrite into a narrow channel within a chip-shaped protrusion of the porous cuticle. For several reasons, the digitiform organ is the most probable candidate for the CO(2)-receptor. Another possible candidate is the distal pore plate.     

The Influences of Epicuticular Wax Disruption and Cutinase Resistance on Penetration of Tomatoes by Colletotrichum gloeosporioides

Conidia of Colletotrichum gloeosporioides germinated on green and ripe tomato fruit with intact epicuticular wax, and formed penetration pegs below melanized appressoria. If the delicate layer of epicuticular wax was distupted by abrasion or removed by solvents before inoculation, apparent increased diffusion of fruit substances into the inoculum stimulated fungal growth, hyphal anastomosis and the production of penetration pegs from hyaline appressoria. This was followed by cutlcle erosion centred on the penetration pegs in green fruit allowing sec-ondary growth of infection hyphae. Due to the development of cutinase resistance when the cuticle became yellow at ripening, no cuticle erosion occurred at penetrations on ripe fruit Since cuticle erosion followed penetration of the cutinase-susceptible cuticle and since penetration peg formation was not hindered by the cutinase cuticle, the process of primary penetration is regarded as mechanical.     

A hundred-year-old question: is the moss calyptra covered by a cuticle? A case study of Funaria hygrometrica

Background and Aims

The maternal gametophytic calyptra is critical for moss sporophyte development and ultimately sporogenesis. The calyptra has been predicted to protect the sporophyte apex, including the undifferentiated sporogenous region and seta meristem, from desiccation. We investigate the hypothesis that this waterproofing ability is due to a waxy cuticle. The idea that moss calyptrae are covered by a cuticle has been present in the literature for over a century, but, until now, neither the presence nor the absence of a cuticle has been documented for any calyptra.

Methods

The epidermis of the calyptra, leafy gametophyte and sporophyte sporangia of the moss Funaria hygrometrica were examined using scanning and transmission electron microscopy. Thicknesses of individual cuticle layers were quantified and compared statistically. The immunochemistry antibody (LM19) specific for pectins was used to locate cell wall material within the cuticle.

Key Results

A multi-layered cuticle is present on the calyptra of F. hygrometrica, including layers analogous to the cuticular layer, cell wall projections, electron-lucent and electron-dense cuticle proper observed in vascular plants. The calyptra rostrum has a cuticle that is significantly thicker than the other tissues examined and differs by specialized thickenings of the cuticular layer (cuticular pegs) at the regions of the anticlinal cell walls. This is the first documentation of cuticular pegs in a moss.

Conclusions

The calyptra and its associated cuticle represent a unique form of maternal care in embryophytes. This organ has the potential to play a critical role in preventing desiccation of immature sporophytes and thereby may have been essential for the evolution of the moss sporophyte.     

The structure of the antennae of the Florida Queen butterfly, Danaus gilippus berenice (Cramer)

Interest in the structure of the antennae of the Florida Queen butterfly arises from the finding that a pheromone is active in their courtship. Light and electron microscopic techniques were used to study the sensilla on the antennae and three types of sensilla with perforated walls were identified. The most common of these are short, thin-walled pegs which are distributed over most of the antennal surface. Long, curved, thin-walled pegs occur in patches on the inner medial antennal surface. Multiple coeloconic sensilla are present having up to 50 pegs in one sensillum. On the outer 28 flagellar subsegments there are two such sensilla per subsegment. In addition there are on the antennae long, thick-walled hairs which are mechanoreceptors and probably also contact chemoreceptors. Sunken pegs, the function of which is not known, occur on the antennae. Grooved sensilla were found with the electron microscope but could not be identified with the light microscope. There was no indication of sexual dimorphism in sensilla types or numbers on the antennae.     

Structure of the cuticle of the alpine weta,Hemideina maori (Saussure) (Orthoptera: Stenopelmatidae)

Sclerotized cuticle segments from the thorax, dorsal abdomen, and ventral abdomen of the alpine, weta Hemideina maori (Saussure) (Orthoptera: Stenopelmatidae) were examined by light microscopy and by scanning and transmission electron microscopy. An epicuticle, exocuticle (outer and inner), mesocuticle, endocuticle, and deposition layer are present in transverse sections. The epicuticle is further composed of a cuticulin layer and inner epicuticle, the latter being finely laminated and containing narrow wax canals that terminate below the cuticle surface. Openings to dermal gland ducts are visible on the surface as are large setae and smaller sensory pegs. Frozen fractured cuticle reveals the presence of horizontal ducts or channels that run laterally within the cuticle. The structure of weta cuticle is compared with that of the common house cricket and arthropods in general.     

Labellar taste organs of Drosophila melanogaster

There are 36 to 42 taste bristles on each half of the labellum of Drosophila melanogaster; most of them are two-pronged with a pouch between them. Some end bluntly with a pore at the tip. Each taste-bristle has two lumina: one is circular, the other crescent-like in cross section. In most bristles four dendrites of chemoreceptor neurons run along the circular lumen. In five to seven taste-bristles only two chemoreceptor neurons are found. A mechanoreceptor neuron sends a dendrite to the base of each taste-bristle. The dendrites are surrounded by four concentrically-arranged sheath cells. The inner cell secretes the cuticular sheath; cells II and III are presumably two trichogens, one secreting the bristle material around the circular lumen, the other around the crescent-like lumen. Cell IV, especially rich in bundles of microtubules, secretes the cuticle of the socket, and corresponds to the tormogen. The neurons have the typical structure found in insect sensilla. In many sensilla one neuron is less electron-dense than the others and may be the water-sensor. On the medial side of the labellum between the pseudotracheae are rows of taste pegs covered by folds. In each peg one chemoreceptor and one mechanoreceptor are found. The number of axons in each labial nerve agrees with the total number of dendrites in all taste organs of each lobe.     

Reappraisal of the pore channel system in the grooved pegs of Aedes aegypti

Pore channels occur along the grooves of lactic acid-receptive grooved pegs on the antennae of female Aedes aegypti. There are about 38 pore openings per groove or about 456 per peg. This finding is in conflict with the previous report that pore channels were extremely rare. The pore channels are of a similar electron density to the cuticle of the peg, making them difficult to see. For this reason many of the pore channels were probably overlooked in the previous study. We could not find a terminal pore in the grooved peg as has been reported. Scanning electron microscopy and negative staining of the pegs revealed a tip of variable shape, usually without a pore. It is possible that 'edge effect' (more secondary electrons escape from edges of objects, making them appear brighter than central regions) leads to an apparent terminal pore. Occasionally pegs have a number of small (20-40 nm) pores in the tip region and these might also have been misinterpreted as a terminal pore. Pore channels appear to be the primary means of entry for air-borne stimuli in these grooved pegs.     

Antennal chemoreceptors of the desert burrowing cockroach, Arenivaga sp

The antennae of Arenivaga have six types of chemoreceptor sensilla. Some of these have unusual morphological features which may be adaptations for survival in a dry habitat. The sensory dendrites are well protected by cuticular structures, and in some receptors stimulatory molecules must pass through long channels or through pores filled with strands to reach the sensory cells. Large grooved pegs (possibly pheromone receptors) are numerous on antennae of adult males, and grooved sensilla are described here in detail for the first time. Thin-walled pegs, present in males and females, do not have pore tubules or hollow filaments as observed in many other insects. Rather, they contain structures designated here as pore strands, since they have a dense core rather than a light center as previously described for pore tubules and filaments. These strands do not appear to be evaginations of the dendritec membrane, but are probably formed in association with the cuticular structures of the sensilla.     

Sense organs on the antennal flagellum of two species of embioptera (Insecta)

Five different kinds of sense organs have been identified on the antennal flagellum of males of Ptilocerembia sp: (1) tactile hairs, (2) thick-walled chemoreceptors, (3) chemoreceptors with thick walls and many pores, (4) thin-walled chemoreceptors and (5) campaniform sense organs. The third type has not been reported previously for other species of insects and combines the characteristics of typical thick-walled and thin-walled chemoreceptors. The campaniform sense organs are situated in sets of three, 120° apart, on the periphery of the distal end of nearly every subsegment. They lie at the transition zone where the thicker cuticle of the subsegment changes to the thin membrane between subsegments.     

Sense organs on the antennal flagellum of the mimosa webworm,Homadaula anisocentra (Lepidoptera,Glyphipterygidae)

Five different types of sense organs were found on the antennal flagellum of Homadaula anisocentra. These were (1) tactile hairs; (2) thick-walled chemoreceptors; (3) thin-walled chemoreceptors of several kinds; (4) styloconic chemoreceptors and (5) small chemoreceptor pegs in shallow depressions. No coeloconic sense organs were seen.     

Fine structure of the aesthetasc hairs ofPagurus hirsutiusculus dana

Summary The thin-walled aesthetasc pegs on the antennules of a small hermit crab,Pagurus hirsutiusculus, were studied by light and electron microscopy. The lumen of each aesthetasc was found to be filled with the dendrites of 300–500 bipolar neurons whose cell bodies lie beneath the base of the aesthetasc. These dendrites are ciliary in nature, having well developed basal bodies and rootlets.Each basal body gives rise to a cilium which divides to form a cluster of slender branches, each of which contains a microtubule running lengthwise. These structures occupy most of the length of the hair.The cuticle of the aesthetasc wall is thin and tenuous. Except for the pore canals in the basal region, we have found no pores at either light or electron microscope level, but as the hair is extremely permeable, we conclude that the cuticle itself may permit the passage of solutions. This permeability of the cuticle and the large numbers of dendrites within support the hypothesis that the aesthetascs are chemoreceptors.     

The structure and function of the gill tufts in larval Amphipterygidae (Odonata:zygoptera)

Larvae of the subfamily Amphipteryginae (Odonata) bear a tuft of tracheal gills on either side of the anus. The two tufts are derived from the laminae sub-anales, and are protected by the non-respiratory epiproct and paraprocts, and by plates derived from the cerci, lamina supra-analis or the lamina sub-analis itself. Each is approximately 1 mm long in mature larvae and comprises a series of repeatedly branching filaments, the terminal twigs of which are 5 to 10 μ in diameter. The total surface area of the tufts is approximately 5.0 mm² in mature larvae of Devadatta, and more in the larvae of Pentaphlebia and Rimanella. Each tuft is connected by a large trachea to the longitudinal tracheal trunk. This large trachea divides many times, eventually forming a dense palisade of tracheoles in the epidermis of the filaments, immediately beneath the thin investing cuticle.     

Fine structure of the aesthetasc hairs of Coenobita compressus Edwards

The aesthetascs, short thin-walled pegs on the antennule flagella of Coenobita clypeatus, a terrestrial hermit crab, are similar to those of other decapod crustacea in containing the dendrites of many bipolar neurons whose cell bodies are grouped in spindle-shaped masses beneath the bases of each hair. The dendrites contain rootlets, basal bodies, and cilia, which divide dichotomously before entering the aesthetasc, so that within the hair, each cilium becomes represented by a group of slender branches. The aesthetascs themselves are short, blunt, and partially recumbent so that each has an exposed and an unexposed side. The cuticle on the exposed side is thinner and more tenuous than that on the protected side, and the dendrite branches are concentrated just underneath. The protected side, on the other hand, is lined with nondendritic supporting cells, and the cuticle is thicker, more lamellar, and probably less permeable. All dendritic elements proximal to the dendrite branches are enclosed within the main body of the antennular flagellum, and the initial segments of the cilia lie within a vacuole. In these respects, the aesthetascs of Coenobita resemble the thin-walled pegs on insect antennae more than they do those of the marine decapods thus far examined. This convergence in the terrestrial forms may be in response to the need to conserve water.     

Fine structure of the cephalic sensory organ in the larva of the nudibranch Rostanga pulchra (Mollusca,Opisthobranchia, Nudibranchia)

Summary The cephalic sensory organ in the veliger larva of Rostanga pulchra is situated dorsally between the rhinophores, emerging as a tuft of cilia. This organ is made up of three types of sensory cells, and based on their morphology have been termed ampullary, parampullary and ciliary tuft cells. The cell bodies of the organ originate in the cerebral commissure, and their dendrites pass to the epidermis as three tracts. Dendrites terminate in the epidermis to form a sectorial field. Axons of these cells run into the mass of neurites in the cerebral commissure but no synapses were observed in this area. Morphological evidence suggests that the cephalic sensory organ may function in chemoreception and mechanoreception related to substrate selection at settlement, feeding, or other behaviors.     

Light microscopic studies on the pineal organ in teleost fishes with special regard to its function

The antennal flagellum of the male sorghum midge is about a millimeter long and may bear over 500 sense organs. These consist of (1) tactile hairs, (2) thin-walled pegs, (3) circumfila and (4) very small pegs of unknown function. Each of the 12 subsegments of the flagellum is divided into two globular nodes and each of these is encircled by a circumfilum of from 6 to 14 loops. The circumfila are attached to the antennal surface by short stalks. The loops of the circumfila have the basic structure of thin-walled chemoreceptors: (1) very small pores in their delicate wall and (2) a lumen filled with branches of dendrites from sensory neurons. The outer surface of the circumfilum is covered with a labyrinth of fine ridges between which the pores are located. Some evidence was obtained that the circumfila are produced in the pupa by bifurcate trichogen cells. The flagellum of the female is shorter than that of the male and composed of 12 cylindrical subsegments. The circumfila of the female lie close to the surface to which they are attached by short stalks. Each is composed of two parts that encircle the subsegment and of two others that run lengthwise between the circles. The surface is nearly smooth, perforated by fine openings and lacks the complex pattern of ridges seen in the male. It also has more dendrite branches but, otherwise, has the same basic structure.     

On the cavity receptor organ (X-organ or organ of Bellonci) of Artemia salina (Crustacea: Anostraca)

Summary The cavity receptor organ (previously X-organ or organ of Bellonci) of Artemia salina consists of ciliated neurons whose cilia protrude into a cavity beneath the cuticle. The neuronal dendrites penetrate a giant accompanying cell and epidermal cells before entering the cavity. The cavity beneath the cuticle, the ciliated neurons and the connexion with the medulla terminalis justifies a homologization with the frontal filament organ of cirripeds and the third unit of copepods. The term cavity receptor is suggested for this organ. It is hardly homologous with the second unit of copepods and the organs described for many malacostracans under the names of sensory pore X-organ or organ of Bellonci. The latter organs are very similar to the cavity receptor but have an internal cavity formed by glial cells.The cavity receptor organ was previously considered neurosecretory but in the light of the present knowledge it is rather sensory although a double function cannot be denied.This investigation was supported by grants (to R. E.) 2760-3 and 2760-4 from the Swedish Natural Science Research Council. One of us (P. S. L.) was on sabbatical leave from the University of Tasmania.     

Sensory cell degeneration in the ontogeny of the chemosensitive sensilla in the labial palp-pit organ of the butterfly,Pieris rapae L. (Insecta,Lepidoptera)

Summary The ontogeny of the chemoreceptive sensilla in the labial palp-pit organ was studied in Pieris rapae by examining twelve successive stages between pupation and emergence of the imago, which takes a period of 160 h under the experimental conditions. Mitoses occur until 20 h after pupation. They lead to anlagen of sensilla, 91% of which are comprised of three sensory cells. However, two sensory cells degenerate in each sensillum during a period of 28 h. The same process occurs in anlagen with four sensory cells resulting in bicellular sensilla. Axons grow out only after the number of sensory cells has been reduced. Further consecutive steps in sensory cell differentiation are: (a) outgrowth of dendritic outer segment and dendrite sheath; (b) outgrowth of trichogen process and change in structure of elongating dendrite sheath; (c) deposition of cuticle and pore tubules in the pegs; (d) retraction of trichogen process; (e) increase in diameter of dendritic outer segment accompanied by increase of microtubule number and appearance of regularly spaced electron-dense bodies at tubular doublets; (f) branching of dendritic outer segment; and (g) transformation of the dendritic branches into curled lamellae and partial destruction of the dendrite sheath. The unique process of sensory cell degeneration is interpreted as an event that revokes a step towards a possible functional improvement of the labial palp-pit organ during further evolutionSupported by the Deutsche Forschungsgemeinschaft (SFB 4/G1)     

The mechanoreceptors on the endophytic ovipositor of the dragonfly Aeshna cyanea (Odonata,Aeshnidae)

This study investigates the mechanoreceptors located on the cutting valvulae of the ovipositor of the dragonfly Aeshna cyanea (Aeshnidae), using both SEM and TEM, with the aim of providing an overview of the sensory equipment of an odonatan endophytic ovipositor. Four kinds of sensilla have been described. Notwithstanding their different external and internal morphology, they show features typical of mechanoreceptors. Three of them are evident along the external surface of the two cutting valvulae in the form of sub-spherical pegs, pit organs type 1 (holes) and pit organs type 2 (depressions), these last are similar to amphinematic scolopidia, while the fourth type is represented by subintegumental mononematic scolopidia having no direct relationship with the cuticle. In spite of their structural differences, the morphology of the described mechanoreceptors is consistent with performing a main role in allowing the perception of compression/stretching of the thick cuticle of the valvulae and their bending due to the pressure acting on the distal end of the ovipositor during substrate penetration. Such an organization is coherent with the need of endophytic Odonata to be able to evaluate the stiffness of the plant where to lay eggs.     

Structure of the stomach cuticle in adult and larvae of the spider crab Maja brachydactyla (Brachyura,Decapoda)

The stomach of decapods is a complex organ with specialized structures that are delimited by a cuticle. The morphology and ontogeny of the stomach are largely described, but few studies have focused on the morphology of its cuticle. This study examined the morphology of the stomach cuticle of cardiac sacs, gastric mill ossicles, cardio-pyloric valve and pyloric filters, and during various stages (zoea I and II, megalopa, first juvenile, and adult) of the common spider crab Maja brachydactyla using dissection, histology and transmission electron microscopy. The results show that cuticle morphology varies among structures (e.g., cardiac sacs, urocardiac ossicle, cardio-pyloric valve, pyloric filters), within a single structure (e.g., different sides of the urocardiac ossicle) and among different life stages. The cuticle during the larval stages is very thin and the different layers (epicuticle, exocuticle, and endocuticle) are infrequently distinguishable by histology. Major changes during larval development regarding cuticle morphology are observed after the molt to megalopa, including the increment in thickness in the gastric mill ossicles and cardio-pyloric valve, and the disappearance of the long thickened setae of the cardio-pyloric valve. The cuticle of all the stomach structures in the adults is thicker than in larval and juvenile stages. The cuticle varies in thickness, differential staining affinity and morphology of the cuticle layers. The structure–function relationship of the cuticle morphology is discussed.