Multiple mode of action of the feeding deterrent,toosendanin, on the sense of taste in Pieris brassicae larvae

Toosendanin, a tetranortriterpenoid isolated from the bark of Melia toosendan, is a feeding deterrent for larvae of Pieris brassicae. By using electrophysiological techniques, it was found that toosendanin stimulates a deterrent receptor cell located in the medial maxillary sensillum styloconicum. Toosendanin also inhibits responses of both the sugar and glucosinolate receptor cell, which are localized in the lateral sensillum styloconicum. The degree of inhibition of the sugar receptor increases with increasing sucrose concentration. The glucosinolate receptor cell shows a reversed reaction: inhibition by toosendanin decreases with increasing sinigrin concentration. Inhibitory effects occur at a toosendanin concentration as low as 10^–9 M and are dose dependent. The taste neurons that respond to amino acids or deterrents in the lateral sensillum, however, are not affected by toosendanin. It is concluded that the sensory code underlying feeding behaviour is modulated by toosendanin via several different peripheral sensory mechanisms.     

Proprioceptive feedback in locust kicking and jumping during maturation

Campaniform sensilla monitor the forces generated by the leg muscles during the co-contraction phase of locust (Schistocerca gregaria) kicking and jumping and re-excite the fast extensor (FETi) and flexor tibiae motor neurones, which innervate the leg muscles. Sensory signals from a campaniform sensillum on the proximal tibia were compared in newly moulted locusts, which do not kick and jump, and mature locusts which readily kick and jump. The activity pattern of FETi during co-contraction was mimicked by stimulating the extensor tibiae muscle. Less force was generated and the spike frequency of the sensory neurone from the sensillum was significantly lower in newly moulted compared to mature locusts. Depolarisation of both FETi and flexor motor neurones as a result of sensory feedback was consequently less in newly moulted than in mature locusts. The difference in the depolarisation was greater than the decrease in the afferent spike frequency suggesting that the central connections of the afferents are modulated. The depolarisation could generate spikes in FETi and maintain flexor spikes in mature but not in newly moulted locusts. This indicates that feedback from the anterior campaniform sensillum comprises a significant component of the drive to both FETi and flexor activity during co-contraction in mature animals and that the changes in this feedback contribute to the developmental change in behaviour.Abbreviations aCS anterior campaniform sensillum - ETi extensor tibiae - FETi fast extensor tibiae motor neurone - FlTi flexor tibiae - pCS posterior campaniform sensillum     

The role of an epipharyngeal sensillum in the perception of feeding deterrents by Leptinotarsa decemlineata larvae

An epipharyngeal taste sensillum in Leptinotarsa decemlineata larvae was studied. Electron microscopy showed that the sensillum is innervated by five neurons. Electrophysiological experiments showed that one of these cells responds to water, a second to sucrose and a third to two feeding deterrents that were also effective in a behavioural test. Receptor cells sensitive to feeding deterrents were not previously reported for L.␣decemlineata larvae or adults. The response of the sucrose-sensitive cell was strongly inhibited by one of the two feeding deterrents and only slightly by the other feeding deterrent. The relationship between the behavioural and electrophysiological results is discussed in order to elucidate the neural code of feeding deterrents in L. decemlineata larvae. We conclude that probably both the response of the deterrent cell and peripheral interactions exerted by feeding deterrents on the sucrose-sensitive cell determine the potency of feeding deterrents. The present results provide a physiological basis for the hypothesis that the presence or absence of feeding deterrents in potential food plants is a decisive cue in food plant selection by L. decemlineata larvae. Accepted: 25 March 1998     

Lamellated outer dendritic segments of a sensory cell within a poreless thermo- and hygroreceptive sensillum of the insect Carausius morosus

Summary A sensillum in a narrow pit with a broad cuticular collar, located in a sensillum field on the 12th segment of the antennae of Carausius morosus, was investigated electrophysiologically. After marking, it was also examined with the transmission and the scanning electron microscopes. The number of sensory cells within the sensillum varies between three and four. One cell, present in half of the sensilla studied, exhibits a simple cilium of the 9×2+0 type as outer dendritic segment. The outer segment of a second unit is noteworthy in that it divides near its ciliary base into two branches. These flatten to form lamellae, then fold and wrap around each other. The remaining two sensory cells bear unbranched or bifurcate outer segments which contain densely packed microtubules. Only these outer segments extend into the cuticular peg; the others end beneath its base. The cuticular peg is devoid of pore systems. Electrophysiological recording yielded evidence that a cold, a dry and a moist air receptor are present. The fourth unit did not respond clearly to stimulation.Supported by the Deutsche Forschungsgemeinschaft (Al 56/6)Research Fellow of the Alexander von Humboldt Foundation     

Hairless is required for the development of adult sensory organ precursor cells in Drosophila

Reduction of the wild-type activity of the gene Hairless (H) results in two major phenotypic effects on the mechanosensory bristles of adult Drosophila. Bristles are either 'lost' (i.e. the shaft and socket fail to appear) or they exhibit a 'double socket' phenotype, in which the shaft is apparently transformed into a second socket. Analysis of the phenotypes conferred by a series of H mutant genotypes demonstrates (1) that different sensilla exhibit different patterns of response to decreasing levels of H+ function, and (2) that the 'bristle loss' phenotype results from greater loss of H+ function than the 'double socket' phenotype. The systematic study of H allelic combinations enabled us to identify genotypes that reliably produce specific mutant defects in particular positions on the bodies of adult flies. This permitted us to investigate the cellular development of sensilla in these same positions in larvae and pupae and thereby establish the developmental basis for the mutant phenotypes. We have found that H is required for at least two steps of adult sensillum development. In positions where 'double socket' microchaetes appear on the notum of H mutant flies, sensillum precursor cells are present in the developing pupa and divide normally, but their progeny adopt an aberrant spatial arrangement and fail to differentiate correctly. In regions of the notum exhibiting 'bristle loss' in adult H mutants, we were unable at the appropriate stages of development to detect sensillum-specific cell types, the precursor cell divisions that generate them, or the primary precursor cells themselves. Thus, the H 'bristle loss' phenotype appears to reflect a very early defect in sensillum development, namely the failure to specify and/or execute the sensory organ precursor cell fate. This finding indicates that H is one of a small number of identified genes for which the loss-of-function phenotype is the failure of sensillum precursor cell development.     

Behavioural and sensory responses to drimane antifeedants in Pieris brassicae larvae

Fifteen drimane compounds were tested for their feeding inhibiting activity in larvae of Pieris brassicae L. (Lepidoptera: Pieridae) when applied to leaf material of the host plant Brassica oleracea L. The antifeedant efficacy of the drimanes was related to their molecular structure in order to identify important functional groups. Of the drimanes tested, those with a lactone group on the B-ring were the most effective feeding inhibitors. Additionally, the sensory responses to 13 of the drimanes were measured. Neural activity was evoked in the deterrent cell in the medial sensillum styloconicum. Also, inhibition of sensory responses to feeding stimulants was found. Results of behavioural and electrophysiological tests were correlated in an attempt to elucidate the sensory code underlying feeding inhibition by drimanes in Pieris brassicae. It was concluded that the response of the deterrent cell in the medial sensillum styloconicum contributes significantly to inhibition of feeding behaviour in larvae of Pieris brassicae.     

Fine structure of the chemoreceptor sensillum in Limulus

Each chemoreceptor sensillum of Limulus polyphemus consists of 6–15 bipolar neurosensory cells with distal processes confined within a single cuticular tubule as they extend to the outside environment. The cuticular tubule, which is enveloped by the cuticulo-tubal cell, opens proximally into a fluid-filled extracellular space through which the dendrite passes before entering the cuticular tubule. Between the neurosensory cells are one to three microvillar cells also exposed to the extracellular space. This space is enclosed by a sheath cell extending proximally from the inner opening of the cuticular tubule and enveloping the proximal portions of the dendrites, the distal portions of the microvillar cells, as well as the distal portion of some neurosensory cell bodies. Most of the remaining portions of the neurosensory cells and microvillar cells are enveloped by neuroglia. Tight junctions occur between the distal portions of the dendrites in or near the cuticular tubule. Each dendrite has a cilium-like segment located where it traverses the extracellular space with a 9 + 0 pattern of fibers. Septuplelayered junctions occur among the proximal portions of some dendrites and some neurosensory cell bodies of the same sensillum. The subjacent processes of the sensillum frequently course proximally as isolated axons before joining nerve bundles. In the chilarial and gnathobasal chemoreceptors these nerve bundles course proximally to neuropile clumps of a peripheral nerve plexus. The presence of numerous synaptic vesicles in the neuropiles suggests that chemical transmission may occur among “en passant” synapses formed by the axons. Proximally the neuropiles are joined to the central nervous system by relatively long nerves.     

The coelocapitular sensillum,an antennal hygro- and thermoreceptive sensillum of the honey bee,Apis mellifera L.

Summary The sensillum coelocapitulum, a hygro- and thermoreceptive sensillum of the honey bee, Apis mellifera, was investigated by electron microscopy. The cuticular apparatus of the sensillum is a mushroomshaped protrusion, devoid of pores, set in a narrow cylindrical pit positioned centrally within a cuticular, shallow depression. There may be three or four receptor cells. Three receptor cells have unbranched sensory cilia, containing densely packed microtubules, which extend distally into the cuticular apparatus and completely fill its cavity. These connecting cilia are of the usual 9+0 type. The fourth receptor, if present, has a thin sensory cilium which terminates beneath the cuticular apparatus. Its connecting cilium has armed outer doublets. The outer cavity is formed by two enveloping cells and is completely sealed off. Lipid deposits are present within the cavity and the tormogen cell. The thecogen cell has scolopale rod-like structures around the inner cavity. Features common to the insect hygro- and thermoreceptive sensilla are discussed in comparison with those of other insects.     

Changes in taste receptor cell sensitivity in a polyphagous caterpillar reflect carbohydrate but not protein imbalance

Caterpillars of the polyphagous arctiid, Grammia geneura, have a single cell in the medial galeal sensillum that responds to some sugars and to some amino acids. After conditioning on artificial diet containing unbalanced amounts of carbohydrate and protein, the responses of this cell alter. After protein-biased food it increases slightly, but after carbohydrate-biased food it decreases. Responses to both sucrose and amino acids change in the same direction and the changes would not provide the information necessary to redress a shortage of protein. The lateral galeal sensillum contains one cell that responds to fructose and another responding to some amino acids. The responses of each of these cells in the lateral sensillum are not consistently affected by conditioning diets. After conditioning for 20 h on a protein- or carbohydrate-biased diet, the insects started to feed without delay if offered carbohydrate-biased diet, but only after a pause if given protein-biased diet. This occurred irrespective of the conditioning diet. The duration of the first feeding bout was also longer on carbohydrate-biased diet and the longest bouts followed protein-biased conditioning.     

Ultrastructure of a possible new type of crustacean cuticular strain receptor in Carcinus maenas (crustacea,decapoda)

A hitherto unknown sensillum type, the “intracuticular sensillum” was identified on the dactyls of the walking legs of the shore crab, Carcinus maenas. Each sensillum is innervated by two sensory cells with dendrites of “scolopidial” (type I) organization. The ciliary segment of the dendrite is 5–6 μm long and contains A-tubules with an electron-dense core and dynein arm-like protuberances; the terminal segment is characterized by densely packed microtubules. The outer dendritic segments pass through the endo- and exocuticle enclosed in a dendritic sheath and a cuticulax tube (canal), which is suspended inside a slit-shaped cavity by cuticular lamellae. The dendrites and the cavity terminate in a cupola-shaped invagination of the epicuticle. External cuticular structures are lacking. Three inner and four to six outer enveloping cells are associated with each intracuticular sensillum. The innermost enveloping cell contains a large scolopale that is connected to the ciliary rootlets inside the inner dendritic segments by desmosomes. Scolopale rods are present in enveloping cell 2. Since type I dendrites and a scolopale are regarded as modality-specific structures of mechanoreceptors, and since no supracuticular endorgan is present, the intracuticular sensilla likely are sensitive to cuticular strains. The intracuticular sensilla should be regarded as analogous to insect campaniform sensilla and arachnid slit sense organs.     

The antennae of neopseustid moths: Morphology and phylogenetic implications, with special reference to the sensilla (Insecta, Lepidoptera, Neopseustidae)

The antennae of Lepidoptera Neopseustidae were examined with the scanning electron microscope. The studied species, Nematocentropus cfr. omeiensis, Neopseustis meyricki, Synempora andesae, Apoplania valdiviana and Apoplania penai possess nine types of antennal flagellum sensilla: multiporous large sensilla basiconica, multiporous thin sensilla basiconica, multiporous small sensilla basiconica, multiporous sensilla trichodea, multiporous sensilla coeloconica; uniporous sensilla chaetica; aporous sensilla chaetica, aporous stylus-shaped sensilla chaetica, aporous sensilla styloconica.The multiporous sensillum type here termed “multiporous large sensillum basiconicum” is unknown from other Lepidoptera and probably constitutes an autapomorphy of the family Neopseustidae. This sensillum type is remarkable by having a single base in female Apoplania and Synempora while in male Apoplania it has a bifid or trifid base, and in male Synempora it is composed of two or three incompletely separated hairs. This may be the first recorded example of a sexually dimorphic lepidopteran sensillum type. The stylus-shaped sensillum chaeticum is a primitive type which occurs only in some lower Lepidoptera.     

Response characteristics of a spider warm cell: temperature sensitivities and structural properties

The sensitivity of a warm cell to temperature stimulation was examined electrophysiologically on the spider Cupiennius salei. The relationship between sensitivity and structure of the warm cell was assessed by comparing both the electrophysiological and electron-microscopic data with those described for insect cold cells. Stimulation of the spider warm cell with slowly oscillating temperature change and steady temperature elicited less sensitive responses than in insect cold cells. These characteristics are reflected in the size of the dendritic membrane area, which is smaller in the spider warm cell compared to the insect cold cells. Rapid step-like temperature change produced in the spider warm cell very sensitive responses when compared with data of insect cold cells. The dendritic tip of the spider warm cell is exposed at a pore on the tip of the sensillum but is covered by the cuticle of the sensillum in the insect cold cells.Dedicated to Richard Loftus on the occasion of his 70th birthday, who pioneered several of the questions addressed in this study     

Chemoreceptor sensillum structure in Limulus

The chemoreceptors of Limulus polyphemus (L.) are polyneuronal sensilla found in the spines of the coxal gnathobases of each walking leg, the spines of the chilarial appendages, and the chelae of all the limbs. Each sensillum contains 6–15 bipolar sensory cells that share a single pore in the cuticle. The dendrites of the sensory cells of each sensillum course to the cuticle together. These attenuate sharply and enter a canal in the cuticle as a very narrow terminal thread. The dendrites retain their identity in the thread, but with the light microscope, they are usually not visible individually. Each thread, consisting of 6–15 dendrites, is accompanied to the cuticular surface by a cuticular tubule found within the canal. The chemoreceptor sensilla of the gnathobase, chilarium, and chela, the temperature organs of Patten, and the flabellar receptor organs all have the same basic organization. In general this is the same structural plan shown by chemoreceptors of other arthropods. Several different mechanisms of peripheral physiological interaction among receptor cells are possible with a sensillum organization like that described here for Limulus.     

Multicellular antennal sensilla containing a sensory cell with a short dendrite and dense-core granules in the insect,Hypogastrura socialis (Collembola): intermolt and molting stages

Summary At the antennal tip of the collembolan insect Hypogastrura socialis two terminal-pore sensilla are located, which, in addition to normally structured and most probably chemosensitive sensory cells, also contain aberrant sensory cells. Portions of these cells resemble chemoreceptors but also shown are features that, as a rule, occur in mechanoreceptors. One cell in each sensillum is remarkable in two characteristics: (1) Its dendritic outer segment does not reach the cuticular outer structures of the sensillum; (2) it contains dense-core granules (diameter 60–110 nm) within its perikaryon, its dendritic inner segment and its axon. Additionally, these two cells do not show lengthening of their dendritic outer segment during molt as do all other sensory cells. Among the fibers of one major branch of the antennal nerve within the head capsule a single axon was observed to contain dense-core granules. This axon was traced to its termination where normal synaptical contacts were found. Based on the assumption that the axon belongs to one of the granule-containing sensory cells two alternative hypotheses are proposed: (1) an individual sensory cell of a sensillum may synthesize a transmitter that is different from that of the other sensory cells of this sensillum; (2) the aberrant cells have lost exteroceptive functions but act as neuromodulatorsSupported by the Deutsche Forschungsgemeinschaft (SFB 4/G1)     

Taste cell responses in the polyphagous arctiid, Grammia geneura: towards a general pattern for caterpillars

The caterpillars of Grammia geneura are polyphagous as individuals. Electrophysiological responses of its medial and lateral galeal styloconic sensilla to 21 amino acids, 6 carbohydrates, 10 chemically diverse plant secondary compounds and two inorganic salts were examined. In the medial sensillum, a single cell responded to 8 amino acids, 3 carbohydrates, and the iridoid, catalpol, which is present in a favored hostplant. In the lateral sensillum, one cell responded to amino acids and another to fructose. Two cells in each sensillum responded to secondary compounds and it is suggested that the same cells are stimulated by inorganic salts. There was no evidence of a separate salt-sensitive cell. Phenylalanine stimulated a deterrent cell in the medial sensillum and was behaviorally deterrent. Some essential amino acids did not stimulate any cells and it is suggested that a small number of amino acids (sometimes non-essential) may serve as indicators of nutrient quality. Sugars probably serve as the primary phagostimulants because they are in relatively high concentrations in plants. It is proposed that taste receptor cells should be categorized primarily by their behavioral effects as phagostimulatory or deterrent, rather than their specific ranges of responsiveness. This would emphasize the basic similarities across taxa.     

马尾松毛虫雄蛾触角毛状感受器的细微结构

马尾松毛虫Dendrolimus punctagus(Walker)雄蛾有一对羽毛状触角。在触角鞭节的每对侧枝的内侧(迎风面)着生许多毛状感受器。每个毛状感受器由几丁质表皮毛及位于其下的三个感觉神经原和三个呈同心排列的辅助细胞-鞘原细胞、毛原细胞和膜原细胞构成。几丁质表皮毛上有许多孔。毛腔内充满感受器淋巴液。感觉神经原发出的树状突伸入毛腔,浸浴于感受器淋巴液内。这些结构特征表明它是一种司嗅觉的化学感受器。雄蛾终生不取食,推断它的嗅觉感受器主要用以感受雌蛾释放的性外激素,帮助寻找配偶。     

Anatomy of the antennal dorsal organ in female of Neodryinus typhlocybae (Hymenoptera: Dryinidae): A peculiar sensory structure possibly involved in perception of host vibration

Neodryinus typhlocybae (Hymenoptera: Dryinidae) is a natural enemy of the planthopper Metcalfa pruinosa, which was introduced from North America into Europe and has become established in various regions as a pest species. Vibrational signals play a crucial role in the communication of M. pruinosa, which appears to be exploited by N. typhlocybae. Scanning and transmission electron microscopy have shown that the antennae of N. typhlocybae females have peculiar and complex sensory structures: deep longitudinal grooves that house long sensilla trichodea, termed here “Antennal Dorsal Organs.” Such structures were not present on male antennae. These sensilla extend for the length of the grooves, without contact with the groove cuticle. Their hair shaft is empty and aporous, and inserted into a specialized socket, underneath which there is a cuticular ampulla‐like chamber. Each sensillum is associated with two sensory neurons: one terminates at the proximal end of the dendritic sheath; the other continues into the sensillum sinus and is enclosed in the dendritic sheath. This second sensory neuron then enters the ampulla‐like chamber through the circular opening, and then terminates with a conspicuous tubular body at the shaft base. The possible involvement of this peculiar structure in the context of host recognition mechanism is discussed. J. Morphol. 277:128–137, 2016. © 2015 Wiley Periodicals, Inc.     

Ultrastructure of chemosensory tarsal tip-pore sensilla of Argiope spp. Audouin, 1826 (Chelicerata: Araneae: Araneidae)

While chemical communication has been investigated intensively in vertebrates and insects, relatively little is known about the sensory world of spiders despite the fact that chemical cues play a key role in natural and sexual selection in this group. In insects, olfaction is performed with wall–pore and gustation with tip-pore sensilla. Since spiders possess tip-pore sensilla only, it is unclear how they accomplish olfaction. We scrutinized the ultrastructure of the trichoid tip-pore sensilla of the orb weaving spider Argiope bruennichi—a common Palearctic species the males of which are known to be attracted by female sex pheromone. We also investigated the congener Argiope blanda. We examined whether the tip-pore sensilla differ in ultrastructure depending on sex and their position on the tarsi of walking legs of which only the distal parts are in contact with the substrate. We hypothesized as yet undetected differences in ultrastructure that suggest gustatory versus olfactory functions. All tarsal tip-pore sensilla of both species exhibit characters typical of contact-chemoreceptors, such as (a) the presence of a pore at the tip of the sensillum shaft, (b) 2–22 uniciliated chemoreceptive cells with elongated and unbranched dendrites reaching up to the tip-pore, (c) two integrated mechanoreceptive cells with short dendrites and large tubular bodies attached to the sensillum shaft's base, and (d) a socket structure with suspension fibres that render the sensillum shaft flexible. The newly found third mechanoreceptive cell attached to the proximal end of the peridendritic shaft cylinder by a small tubular body was likely overlooked in previous studies. The organization of tarsal tip-pore sensilla did not differ depending on the position on the tarsus nor between the sexes. As no wall-pore sensilla were detected, we discuss the probability that a single type of sensillum performs both gustation and olfaction in spiders.     

Fine structure of the terminal organ of the house fly larva,Musca domestica L.

Summary The terminal organs of the cephalic lobes of the house fly larva, Musca domestica L., were studied by scanning and transmission electron microscopy. Six different types of sensilla were found: (1) papilla sensillum, (2) pit sensillum, (3) spot sensillum, (4) modified papilla sensillum, (5) knob sensillum, and (6) scolopidium. The papilla, pit, spot, and modified papilla sensilla have the essential structure of contact chemoreceptors, i.e., the unbranched dendritic tips are exposed externally through a single opening. However, a tubular body, which is a characteristic structure of tactile setae, is also present in some of the dendritic tips. We assume these sensilla serve a dual function—contact chemo- and mechanoreception. The role of the knob sensilla is obscure. The scolopidia present in the dorsal and the terminal organ are probably stress detectors. Two basal bodies occur in the dendritic ciliary region of all sensilla. Both of the basal bodies (except in the scolopidia) give rise to the distal ciliary microtubules as well as the proximal rootlets.This research was supported in part by the Office of Naval Research, PHS Research Grant EC-246 and NIH Training Grant ES-00069. Paper No. 3608 of the North Carolina State University Agricultural Experiment Station journal series. The advise of R. A. Steinbrecht is gratefully acknowledged.