Structure of galeal sensory complex in adults of the red turnip beetle,Entomoscelis americana brown (Coleoptera,Chrysomelidae)

Summary The internal and external structure of the galeae of the adult red turnip beetle, Entomoscelis americana, was studied using SEM and TEM. The galea broadens from base to truncated tip and its sides are of thick, sculpted cuticle invested with pores and coarse spines. The tip is of thinner, flexible cuticle covered with 8–12 uniporous, blunt-tipped apical pegs and a single, aporous, sharply-pointed apical hair.The coarse spines are singly innervated probable mechanosensilla owing to the tubular body at the distal end of the dendrite. These sensilla likely act as tactile hairs monitoring galeal-effected movements of food particles into the functional mouth. The pores are associated with glands within the galea. The function of the presumed secretion is not known but may be to keep objects and dried saliva from sticking to the mouthparts.The apical pegs are innervated by five neurons, each producing a single dendrite. Four dendrites enter the single peg lumen and communicate with the terminal pore. The fifth differentiates into a tubular body that inserts into the peg base. These are typical insect contact chemosensilla that, because of their location, would taste incoming food.The apical hair has no pores but is innervated by two neurons, each extending a dendrite into the hair lumen in chemosensillar fashion. The sensory mode of this sensillum is unknown but is probably not mechanoor chemoreception. Many of its features, reminiscent of taste hairs, lead us to hypothesize that it represents a one-time chemosensillum recently modified to a new form and sensory mode.Because larval and adult E. americana share similar food plant requirements, we hypothesize that similarities will be seen in their mouthpart sensilla. Comparisons of the adults and larvae show the common features between their respective galeal taste hairs are only those of insect contact chemosensilla in general. However, the adult apical hair and the larval medial sensillum show striking specific structural similarities. We propose that these are true structural and functional homologues.     

Fine structural analysis of palpal receptors in the tick Amblyomma americanum (L.)

Summary Palps of the tick Amblyomma americanum (L.) (Acarina: Ixodidae; nymphal stage) were studied by scanning and transmission electron microscopy. The terminal palp segment (IV) bears the so-called palpal organ, a cluster of 10 short, blunt-tipped sensilla. All sensilla (except for the center sensillum) receive a dual innervation: 2 mechanoreceptive dendrites which terminate in the socket membrane plus several chemoreceptive dendrites (4–12) which enter the lumen. The thick-walled cuticular shaft possesses 2–3 small pore openings (100 Å) below the tip, thus establishing communication between dendrites and environment. Two structurally different types of palpal sensilla exist: The A-type has a characteristic doublelumen and always contains 4 dendrites, the B-type features a single lumen and a specially layered cuticular shaft with 6–12 dendrites. The fine structure of the tick palpal receptors corresponds closely to that of known contact chemoreceptors in insects.This research was supported in part by a contract with the Office of Naval Research (R. C. Axtell, principal investigator), and by NIH Training grant ES 00069. Paper no. 3700 of the Journal Series of the North Carolina State University Agricultural Experiment Station, Raleigh.     

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.     

Electrical impedance of the labellar taste hair of the blowfly,Calliphora erythrocephala MG.

Summary The impedance characteristics (resistance and phase angle) were measured of the labellar taste hair of Calliphora erythrocephala by recording the values between the base and tip of intact and tip-amputated hairs of young and old flies.Measurements made at 30 Hz to 20 kHz indicated frequency independent values with changes in phase angle up to about 1 kHz and complete bypassing of the insulating cuticle at 15 to 20 kHz.Measurements made at 0.9 kHz with intact and amputated hairs showed a low change in phase angle and thus a negligible reactive component. Subsequently these values were treated as the resistive component of the impedance. Amputation of the tip always caused a drop in impedance of about 30 MOhm.Calculations based on known morphologic data allowed the conclusion that the measurements of intact hairs at slight dipping of the tip have been made through both channels and not the dendrite-containing channel alone; consequently the pore distad of the dendritic endings must have an electrolytic connection to both channels of the taste hair. Slightly deeper dipping of the hair tip (5 or less) resulted in 4 to 7 MOhm reduced impedance which indicates a second pore or opening in the greater tip region.This work was partially supported by National Science Foundation Grant GB-13500.     

Contacts of pore tubules and sensory dendrites in antennal chemosensilla of a silkmoth: Demonstration of a possible pathway for olfactory molecules

Antennal olfactory hairs of Antheraea polyphemus were investigated by means of transmission electron microscopy. Adequate preservation of dendrites and extracellular pore tubules is obtained by mechanical opening of the hair lumen and subsequent chemical fixation. The dendritic membrane has a cell coat. The dendrites contain microfilamentous structures in addition to their cytoplasmatic microtubules. The extracellular pore tubules traverse the hair cuticle and reach into the hair lumen for maximally 350 nm. Their diameter varies between 20 and 40 nm, depending on the preparation method. They consist of an electron-dense wall and an electron-lucent core. The wall has a helical substructure and is covered with a fuzzy coat. Contacts of pore tubules and dendritic membranes occur wherever dendrites are near the inner surface of the hair cuticle. Some of the pore tubules terminate approximately at right angles on the dendritic membrane, others lie against the membrane. The contact seems to be made via the surface coats of the tubules and the membrane. The structure of pore tubules which had been negatively stained with uranyl acetate is similar to the conventionally thin-sectioned material. The observations provide support for earlier assumptions that pore tubules are the pathways by which odor molecules reach the dendritic membrane.     

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 hair-peg organs of the shore crab,Carcinus maenas (Crustacea,Decapoda): Ultrastructure and functional properties of sensilla sensitive to changes in seawater concentration

Summary The hair-peg organs of the shore crab, Carcinus maenas, are modified hair-sensilla. A small hair shaft (peg) is surrounded by a tuft of solid cuticular bristles (hairs). Each hair-peg organ is innervated by 6 sensory neurons, 2 of which have scolopidial (type-I) dendrites. The outer segments of all dendrites pass through a cuticular canal extending to the articulated hair base in which the 2 type-I dendrites terminate. The other 4 (type-II) dendrites reach the clavate tip of the hair shaft and have access to a terminal pore and a large sickle-shaped aperture. Three inner and 8–12 outer enveloping cells belong to a hair-peg organ. The innermost enveloping cell contains a scolopale, which has desmosomal connections to the ciliary rootlets of the type-I dendrites. An inner and an outer sensillum lymph space are present. The ultrastructural features of the dendrites and the cuticular apparatus indicate that the hair-peg organs are bimodal sensilla, comprising 2 mechano- and 4 chemosensitive sensory neurons. Extracellular recordings from the leg nerve indicate that the chemosensitive neurons of the hair-peg organs respond to changes in seawater concentration in the physiological range of Carcinus maenas.Supported by the Deutsche Forschungsgemeinschaft (SFB 45/A1; W. Gnatzy)     

The cercal receptor system of the praying mantid,Archimantis brunneriana Sauss.

Summary The cerci of the praying mantid, Archimantis brunneriana Sauss., are paired segmented sensory organs located at the tip of the abdomen. Basally the cercal segments are slightly flattened dorso-ventrally and are fused to such a degree that it is difficult to distinguish them. Distally the segments become progressively more flattened laterally and their boundaries become more obvious.Two types of sensilla are present on the cerci, trichoid sensilla and filiform sensilla. Trichoid hairs are longest on the medial side of the cerci and toward the cercal base. On the proximal cercal segments they are grouped toward the middle of each segment while they are more uniformly distributed on the distal segments. Filiform sensilla are found at the distal end of each segment except the last and are most abundant on the middle segments of the cercus. Both the number of cercal segments and the number of sensilla are variable. Trichoid hairs are highly variable in appearance from short and stout to long and thin. They arise from a raised base, have a fluted shaft, and some have a pore at the tip. They are innervated by from one to five dendrites, one of which is always considerably larger than the others. Some of the dendrites continue out into the shaft of the hair.Filiform hairs have fluted shafts and are mounted in a flexible membrane within a cuticular ring in a depression. They are innervated by a single large sensory neuron, the dendrite of which passes across a flattened area on the inner wall of the lumen of the hair. The dendritic sheath forms the lining of the ecdysial canal and is therefore firmly attached to the hair. The dendrite is attached to the sheath by desmosomes distally and is penetrated by projections of the sheath more proximally. A fibrous cap surrounds the dendrite and may hold it in place relative to the hair.The cercal receptor system of Archimantis is compared to those of cockroaches and crickets.     

The structure of the postantennal organ in Onychiurus sp. (Insecta: Collembola) and its connection to the central nervous system

Summary The postantennal organ in Onychiurus (group armatus) is a sensory organ comprising one sensory cell, several enveloping cells and cuticular structures.The perikaryon of the sensory cell is located in the central nervous system and distally gives off a dendrite in which one inner and two outer segments are distinguishable. Two ciliary structures connect the outer dendritic segments with the inner segment. The outer segments divide repeatedly, basal to the cuticular structures, into small branches which end distally beneath the cuticular wall. The wall of the cuticular structures is very thin and is pierced by numerous funnel-shaped pores. The pores are filled with electron-dense material which forms a continuous sheath underneath the cuticle. This material encases the small dendritic branches and the processes of the enveloping cells which occupy the lumen of the cuticular structures. There are three types of enveloping cells: one inner, several outer and one basal. Their processes differ in the manner in which they envelop the various regions of the dendrite.At the beginning of moulting outer dendritic branches are not found within the cuticular structures of the organ. They may be assumed to retract inwardly. However, in the later stages, when the cuticle is fully formed, the outer dendritic segments appear to divide. It is assumed that the small dendritic branches reach their targets before ecdysis. The electrondense material which clogs the intermoult cuticular pores is absent until the final stages of the moulting cycle.Supported by a grant from the Deutscher Akademischer Austauschdienst.     

Reconstruction and morphometry of silkmoth olfactory hairs: A comparative study of sensilla trichodea on the antennae of male Antheraea polyphemus and Antheraea pernyi (Insecta,Lepidoptera)

Summary Olfactory trichoid hairs on the antennae of male Antheraea silkmoths were reconstructed with respect to the following parameters: number, shape, course, and dimensions of outer dendritic segments as well as the numbers of their microtubules; inner and outer dimensions of the cuticular hair shafts; and number and distribution of pores and pore tubules in the hair walls. The smallest distances between dendritic membranes and inner hair surfaces were determined with respect to the possibility of pore tubule contacts. It was shown that most hairs contain one thick and one, or frequently two, thin dendrites. The number of microtubules in the dendrites is correlated with dendrite diameter, which decreases towards the hair tip. The dendrites form numerous swellings and constrictions: this beading occurs especially along the thin dendrites. The dendrites do not run straight, but rather follow a sinuous course in the hairs. The density of wall pores is lowest in the basal region of the hairs. Only in relatively few places do the dendritic membranes get near enough the hair walls to come into the probable range of the pore tubules. In the sensilla trichodea of A. polyphemus, the hairs as well as the dendrites have markedly smaller diameters than in A. pernyi.     

Ultrastructure of aesthetasc innervation and external morphology of the lateral antennule setae of the spiny lobster Panulirus interruptus (Randall)

Summary Six types of setae and one type of cuticular depression were examined on the lateral antennule of the spiny lobster Panulirus interruptus using scanning electron microscopy. The organization and ultrastructure of the innervation of the most numerous setal type, the aesthetasc, were investigated using light-and transmission electron microscopy.Each aesthetasc is innervated by approximately 300 bipolar neurons whose sensory dendrites penetrate the hair and extend toward the tip, and whose axons project towards the central nervous system. The neuronal somata and two types of glia form a cluster within the antennular lumen. The inner sheath-cell somata encircle the dendritic tract distal to the sensory somata. These cells appear to extend distal processes which wrap the dendritic tract to the base of the aesthetasc. Elongate outer sheath cells are interposed between the glia-wrapped dendritic tract and the hypodermis which underlies the antennule cuticle. A continuous investment of neural lamella separates the hypodermis, the entire cluster of somata, and sensillar nerve from the antennule lumen. The organization of the neuronal somata and their association with outer and inner sheath cells in this marine species appear similar to those of crustaceans from freshwater and terrestrial habitats.     

Development of antennal sensilla during moulting inNeomysis integer (Leach) (Crustacea,Mysidacea)

Summary The sensilla are associated with 6 enveloping cells. The innermost enveloping cell (e 1) secretes the dendritic sheath (=thecogen cell). All other enveloping cells are involved in the formation of the outer cuticular apparatus in secreting the cuticle of a definite region of the new hair shaft.The development of the new sensilla begins when an exuvial space expands between old cuticle and epithelium. The newly forming hair shafts lie folded back in an invagination of the epidermal tissue. Only a distal shaft part projects into the free exuvial space. The cuticle of the distal and middle shaft region is secreted by the three middle enveloping cells (e 2–e 4) (=trichogen cells), which are arranged around the dendritic sheath.The wall of the cylinder, in which the distal shaft is situated, is formed by the cuticle of the future proximal shaft region. It is secreted by the outer enveloping cells (e 5 and e 6). Furthermore, both enveloping cells form the hair socket (=trichogen-tormogen cells).The outer dendritic segments encased within a dendritic sheath run up through the newly formed hair shaft and continue to the old cuticular apparatus. The connection between sensory cells and old hair shaft is maintained until ecdysis. On ecdysis the old cuticle is shed and the newly formed shaft of the sensillum is everted like the invaginated finger of a glove. The dendritic sheath and the outer dendritic segments break off at the tip of the new hair shaft. Morphologically this moulting process ensures that the sensitivity of the receptors is maintained until ecdysis.The internal organization of the sensory cells shows no striking changes during the moulting cycle. An increased number of vesicles is accumulated distally within the inner dendritic segments and distributed throughout the outer segments of the dendrites. The cytoplasmic feature of the enveloping cells indicates that synthesis and release of substances for the cuticular apparatus of the new sensillum take place.     

Simultaneous chemical and electrical stimulation of labellar taste hairs of the blowfly Calliphora vicina

When recording from the tip of insect taste hairs, responses to chemical stimulation may be influenced by electrical currents, such as the preamplifier's input bias current. The effect of electrical currents on firing frequency of the salt receptor cell to KCl and NaCl stimulation was determined in labellar ‘aboral’ and ‘adoral’ taste hairs of the blowfly Calliphora vicina. Negative currents always decreased spike frequency, whereas positive currents either increased it, or did not change it significantly. Spike frequency changed less than 1% per 5 × 10^?11 A.A consistent picture of the electrophysiology of blowfly taste hairs is given. It includes a distal pore, present in the dendrite-free lumen of the hair. It abandons the concept of a generator current that transmits excitation from the distal, chemoreceptive part of the taste cell dendrite to the action potential generator in or near the taste cell body. The experimental results are interpreted on the basis of this picture. It is concluded that the ‘electrophoretic effect’ of the electrical current is very small. Thus, the measured effect should mainly be due to a ‘direct effect’ of electrical current on electrically excitable structures in the salt receptor cell, particularly in its dendrite.     

Ultrastructure of the peg and hair sensilla on the antenna of larval Aedes aegypti (L.)

The antenna of fourth instar larvae of Aedes aegypti has one peg organ of a basiconic type innervated by four neurons. The dendrites are ensheathed to near their terminations at the peg tip by an electron-dense dendritic sheath and by a cuticular sheath. They have easy communication by diffusion with the external environment only at the tip through a peripheral ensheathing membrane and six slit-channels. One of the dendrites resembles a tubular body proximally and may be mechanoreceptive. The peg generally appears to be a contact chemoreceptor. There are three antennal hairs of a typical sensillum trichodeum type innervated at the base by one neuron each. An intricate terminal mechanism at the insertion of the dendrite in the hair is described. These are believed to be tactile hairs. There are also three antennal hairs each innervated by two neurons. The dendrite from one terminates at the base similar to that of a tactile hair, and is believed to function in a similar mechanoreceptive manner. The dendrite from the second neuron extends naked along the length of the hair lumen. It is believed to be primarily chemoreceptive, in a slow-acting general sensory function. In all the sensilla there appear to be secretions produced in the junction body regions of the dendrites, and there is evidence for accumulation of secretory materials in the dendritic tips in some of the sensilla.     

The external morphology of contact-chemoreceptive hairs of flies and the motility of the tips of these hairs

The external morphology of contact-chemoreceptive hairs (taste hairs) of six fly species, Calliphora vicina, Lucilia caesar, Musca domestica, Phormia terranovae, Sarcophaga carnaria and Stomoxys calcitrans, is described. The species can be distinguished by the differences between the patterns of taste hairs at the ventral side of their prothoracic tarsi. Taste hairs can be subdivided into morphological types, using the shape of the cuticle around the apical pore as criterion, even though this shape changes slightly on opening and closing of the pore. Light microscopical studies reveal that the nature and osmolarity of stimuli are decisive for the effect stimuli have on the shape of the top of the labellar hairs. The motions of the apical cuticle appear to be reversible. Gentle ultrasonic treatment preserves the shape of the cuticle of the top and the diameter of the pores on fluid stimulation. This technique makes it possible to study the effect of a previous stimulation on both tarsal and labellar hairs with the scanning electron microscope. It is supposed that stimuli can affect cuticular components around the pore, producing volume changes in that cuticle which alter the diameter of the pore.     

Permeability of tarsal sensilla in the tick Amblyomma americanum L. (Acarina, Ixodidae)

Ticks were submerged in silver-protein solution, prior to fixation for electron microscopy, in order to trace the pathway of molecules in supposed tarsal chemoreceptors. Sensilla with radially arranged cuticular canals (100-200 A in diameter) leading to the centrally located dendrites show silver granules inside the canals and in the central lumen, thus directly making contact with the dendrites. Sensilla with large, plugged pores (1200 A) exhibit an accumulation of silver granules in the pore openings but no granules (about 50 A in diameter) were observed penetrating into the lumen. Apparently silver granules could diffuse in, but not through the material which suspends the pore plugs. It is suggested that this material corresponds to the 'pore tubules' in insect olfactory sensilla and that it may play an essential role in transmitting a chemical stimulus from the environment to the dendrites.     

Some USDA studies on the soybean-Rhizobium symbiosis

Summary The ecology, strain evaluation, genetics of host strain interactions and physiology of nitrogen fixation ofRhizobium japonicum in association with the soybean,Glycine max, were studied. Results of inoculation experiments with selected strains ofRhizobium japonicum indicated that indigenous strains occupied most of the nodules of soybeans grown in highRhizobium japonicum populated soils. Nodule sampling indicated that inoculation did not result in quicker nodulation or a higher incidence of root nodules (primary or secondary) than uninoculated checks. Rhizosphere studies indicated that colonization by introduced strains did occur but did not compete successfully with field strains for nodule sites. Recovery of specific serological types from nodules was influenced by planting intervals. The distribution of the serotypes varied with the time of planting and the age of the plant. Temperature studies indicated that the distribution of serotypes recovered from the nodules was influenced by temperature. Field studies showed the selectivity of soybean genotypes on strains ofRhizobium japonicum. Some strains were more common in the nodules of some varieties than in others. Closely related varieties had similar populations in their nodules. Three genes which control nodule response in soybeans are reported. Nitrogen fixation profiles were determined for some variety-strain interactions. Combinations previously classified as inefficient showed some nitrogenase activity as measured by the acetylene reduction technique. Research Microbiologist; Research Agronomist; Research Plant Physiologist, Soybean Investigations, Crops Research Division, Beltsville, Md. (USDA, ARS); and Plant Pathologist currently located at Michigan State University, East Lansing, Michigan.     

Rice protein mutant expressed in liquid suspension cultures: chitinases, β-glucanases and other proteins

Summary A rice mutant with unique protein expression/ transport properties has been established as cells in liquid suspension and partially characterized. Mutants were originally recovered from anther calli grown for three cycles at inhibitory levels of lysine + threonine and one cycle of S-(2-aminoethyl)cysteine. Cell suspension cultures were started from high lysine-containing seeds regenerated from the inhibitor selections. Cultures of the mutant produce 2 times as much protein per unit weight as is produced by the control. Significant portions of the proteins are exported from the cells into the surrounding medium. The mutant also has 20% greater lysine content in the exported protein than the control. This cell suspension line should be particularly useful for biochemical and molecular studies on protein synthesis and processing phenomena in cereals.Research done under the auspices of the USDA, ARS, Plant Science Institute, Plant Molecular Biology Laboratory, Beltsville, Md 20705, USA     

Fine structure and role in behavior of sensilla on the terminalia of Aedes aegypti (L.) (Diptera: Culicidae)

The terminalia of male and female Aedes aegypti (L.) bear numerous hairs of various shapes and lengths, all of which are mechanoreceptors. Each hair is innervated by one bipolar neuron which contains ciliary rootlets, two basal bodies, and a region assuming the structure of a non-motile cilium. At the distal tip of the dendrite is a tubular body, a characteristic of cuticular mechanoreceptors. Covering the outer dendritic segment is a cuticular sheath which ends proximally in a net-like felt-work and distally attaches to the hair base. Each hair sensillum has two sheath cells. Presumed efferent fibers are associated with the sheath cells. On the insula of the female terminalia are a few campaniform sensilla, the domes of which are raised into small pegs. The sensilla on the terminalia function in copulation and oviposition and probably in warning. A sequence of neurological events is traced for copulation and oviposition. Other cuticular structures, viz., scales, microtrichia, acanthae, and aedeagal spines, which occur on the terminalia are not innervated.     

The spiral glands of Nereis

Summary The spiral organs of Nereis have been shown to be compound glands and not photoreceptors. The ducts of two or three types of secretory cells attach themselves in a serial manner to a spirally wound axial columella which lies just below the cuticle. The large intra-cellular ducts terminate in a number of fine ducts which penetrate the columella and open through it into the lumen of the gland. This communicates to the outside through a pore in the cuticle. The secretions are muco-polysaccharides which are probably mixed in the lumen before discharge.We should like to acknowledge the support of this work by the Science Research Council.