Sensory organs on the body parts of the bed-bug Cimex hemipterus fabricius (Hemiptera : Cimicidae) and the anatomy of its central nervous system

Anatomy of the sensory organs on the prominent body parts of the adult bed-bug Cimex hemipterus (Hemiptera: Cimicidae) and its central nervous system (CNS) was studied by light, transmission, or scanning electron microscopy. The distal tips of antenna and rostrum were found to have rich complements of sensilla. The antenna has both olfactory and gustatory sensilla. Olfactory sensilla project to the antennal lobe organized in the form of glomeruli, while the 2nd component, presumably from gustatory sensilla, projects to the suboesophageal ganglion. The ultrastructure of the sensory pegs on the rostrum of C. hemipterus does not resemble the chemosensilla of adult insects; rather they resemble the larval sensilla of Drosophila melanogaster in the maxillary organ. Earlier we believed this to be a gustatory organ. A few similar sensilla also occur on the antenna, indicating its multimodal role. Amongst the 3 types of sensory hairs located on legs, there are only a few gustatory hairs (7–10 hairs) on the tibia. The pointed and serrate mechanosensory hair types occur in abundance; the serrate type are prominently present on the lateral surface of the legs. On other parts of the body such as the thorax or abdomen, serrate hairs are most abundant. Both the distal segment of antenna and rostrum are invested by 2 nerves, where the axon counts of the 2 antennal nerves are 380 and 425, while each rostral nerve on average has 205 axons. Abundant clusters of microtubules were found in the brain, thoracio-abdominal ganglia, leg-nerves, and the space between muscles and cuticle. These conspicuous microtubule-clusters occur in interaxonal space, mainly glial cells, in the nervous system. In addition, the glial cells have osmiophilic junctions amongst themselves. A novel “hinge and joint” system, which controls the cross-section of the food canal and the salivary duct in an inversely related manner, was found in the rostrum of the bed-bug.     

Antennal sensilla and their possible functions in the host-plant selection behaviour of Phenacoccus manihoti (Matile-Ferrero) (Homoptera : Pseudococcidae)

Nine different types of sensilla have been identified on the antenna of the cassava mealybug Phenacoccus manihoti (Homoptera : Pseudococcidae) with scanning and transmission electron microscopes. Trichoid sensilla, distributed on all segments of the antenna and innervated by a single mechanoreceptive dendrite, have the characteristics of exteroceptors. A campaniform sensillum located on the pedicel and one basiconic sensillum on the flagellum have the characteristics of proprioceptors. Coeloconic sensilla, located ventrally on the pedicel and flagellum, related to poreless sensilla with inflexible sockets, have the characteristics of thermo/hygroreceptors. Uniporous sensilla with a mechanoreceptive dendrite (smooth pegs P1 and P2, grooved pegs P3) and multiporous chemosensilla (grooved pegs P4 and P5), present on the tip of the flagellum, have, respectively, the characteristics of gustatory and olfactory receptors. The results of this study seem to suggest that the cassava mealybug has sensory equipment on its antennae that can detect, by olfaction and contact, chemicals released by the plant.     

Structure of sensilla, olfactory perception, and behaviour of the bedbug, Cimex lectularius, in response to its alarm pheromone

When deprived of the terminal antennal segments, male and female bedbugs failed to respond to their alarm pheromone and to their assembling scent. Trans-oct-2-en-1-al or trans-hex-2-en-1-al, being the major constituents of the former, induce in adults and larvae of Cimex lectularius a typical alarm behaviour resulting in dispersal of assembled bedbugs; the rapidity of escape depends on the aldehyde concentration in the air. The behavioural threshold for adults is about 9×10¹⁴ molecules of trans-oct-2-en-1-al or 6×10¹⁵ molecules of trans-hex-2-en-1-al per ml air.The distal part of the terminal antennal segment of C. lectularius reveals the following sensilla: bristles (type A1), immersed cones (type B1), plates (type B2), grooved pegs (type C), smooth pegs (type D), hairs with even (type E1), and uneven wall thickness (type E2). The number and distribution of these sensilla is relatively constant and similar in both sexes, but differs slightly in neonate larvae. The pegs and hairs of types C, D, E1 and E2 were shown to have porous walls, a prerequisite for olfactory function.Receptor potentials were recorded from olfactory sensilla of types E1 and E2 after stimulation with trans-hex-2-en-1-al and trans-oct-2-en-1-al. The minimal concentration of trans-hex-2-en-1-al evoking a receptor potential is about 2×10¹⁰ molecules per ml air. The above olfactory sensilla were found to respond also to hexan-1-al, but almost no responses to pentan-1-al, butan-1-al, trans-hex-2-ene, and trans-oct-2-ene were observed. A minimum chain length of six carbons atoms and a terminal carbonyl group are molecular prerequisites for optimal odorant activity, while the presence of a Δ²-double bond is not essential for stimulation of the alarm pheromone receptors of the bedbug.     

Off-host aggregation behavior and sensory basis of arrestment by Cimex lectularius (Heteroptera: Cimicidae)

The bed bug, Cimex lectularius, aggregates under filter paper disks previously stained by adults. A multiple-choice assay was used to determine differences in aggregation behavior among two strains, multiple lifestages, and levels of starvation. There were no differences in level of aggregation between established and recently derived strains, or among adults and nymphs of different instars. Propensity to aggregate decreased with time since feeding, but preference for stained disks remained high. We also examined which sensory structures mediate aggregation, and whether antennectomy affected movement, orientation, and arrestment under stained disks. Bed bugs that were left intact, blinded, or surgically altered by the removal of probosci or the distal antennal segments exhibited high levels of aggregation under stained disks. However, the removal of the pedicel significantly reduced aggregation compared to intact bugs. Video recordings of movement and orientation by bugs with intact, partial and complete antennectomies demonstrated that neither partial nor complete antennectomies affected walking speed, path straightness, direction of movement or frequency of encounters with either stained or clean disks. However, complete removal of both antennae significantly reduced the percentage of encounters with stained disks that resulted in arrestment. These findings suggest aggregation by bed bugs is a result of arrestment mediated by direct, close-range contact between sensilla on the pedicel and stained disks.     

Antennal sensilla of the click beetle,Melanotus villosus (Geoffroy) (Coleoptera: Elateridae)

The typology, number and placement of antennal sensilla of the click beetle Melanotus villosus (Geoffroy) (Coleoptera: Elateridae) were studied using scanning electron microscopy. On both the males and females the antennae are made up of the scape, pedicel and nine flagellomeres. Two types of basiconic sensilla, three types of trichoid sensilla, one type of styloconic sensilla, one type of chetoid sensilla, dome-shaped sensilla, grooved pegs, and Böhm sensilla all appear on the antennae of the beetles of both sexes, with the exception of trichoid sensilla type II, whose large number (average of 1635 hairs per antenna) was found only in male beetles. Sensilla trichodea type II evidently respond to the sex pheromone produced by the female beetle. Unlike the other two click beetles, studied up till now, Agriotes obscurus and Limonius aeruginosus, the trichoid and basiconic sensilla of M. villosus, whose proven or assumed function is olfactory, are located predominantly on the flagellomeres ventral extensions. It is assumed that the placement of the olfactory sensilla, mainly on the ventral side of M. villosuss antennae, and their more or less even distribution on the flagellomeres, can be seen as morphological adaptation of this species of insect, whose specific behavioural reaction of olfactory searching is flying, both before and after contact with an odour plume.     

The formation of the antenna sensory apparatus in some bug (Heteroptera) species in the course of their postembryonic development

In the antenna sensory apparatus of bugs Coreus marginatus, Cimex lectularius, and Rhodnius prolixus sensilla of the four main types are identified: chaetica, trichodea, basiconica, and coeloconica. Chaetoid sensilla are differentiated into two subtypes: sensilla with cogged cuticles and those with smooth ones; trichoid sensilla were divided into long pointed and short ones with blunt tips. In larvae and adults of R. prolixus trichobothria (long filiform hairs) were found on the medial side of pedicellum. The postembryonic changes in the quantitative and qualitative composition of the antenna sensory apparatus were assessed using biometric analysis. The greatest increase of sensory organs was observed upon the nymphal ecdysis from the 5th instar to adult.     

Ultrastructure of chemoreceptive tarsal sensilla in an armored harvestman and evidence of olfaction across Laniatores (Arachnida,Opiliones)

Harvestmen (Arachnida, Opiliones) are especially dependent on chemical cues and are often regarded as animals that rely mainly on contact chemoreception. Information on harvestman sensilla is scarce when compared to other arachnid orders, especially concerning internal morphology. Using scanning (SEM) and transmission (TEM) electron microscopy, we investigated tarsal sensilla on the distal tarsomeres (DT) of all leg pairs in Heteromitobates discolor (Laniatores, Gonyleptidae). Furthermore, we explored the typological diversity of sensilla present on the DT I and II in members of the suborder Laniatores, which include two thirds of the formally described opilionid fauna, using species from 17 families representing all main laniatorian lineages. Our data revealed that DT I and II of H. discolor are equipped with wall-pored falciform hairs (two types), wall-pored sensilla chaetica (two types) and tip-pored sensilla chaetica, while DT III and IV are mainly covered with trichomes (non-sensory) and tip-pored sensilla chaetica. The ultrastructural characteristics support an olfactory function for all wall-pored sensilla and a dual gustatory/mechanoreceptive function for tip-pored sensilla chaetica. Based on our comparative SEM survey, we show that wall-pored sensilla occur in all investigated Laniatores, demonstrating their widespread occurrence in the suborder and highlighting the importance of both legs I and II as the sensory appendages of laniatorean harvestmen. Our results provide the first morphological evidence for olfactory receptors in Laniatores and suggest that olfaction is more important for harvestmen than previously thought.     

Innervation of the cercal sensilla on the ovipositor of the Australian sheep blowfly (Lucilia cuprina)

ABSTRACT. The ovipositor of the female sheep blowfly, Lucilia cuprina (Wied.) (Diptera: Calliphoridae), has a complement of cercal sensilla that includes long, medium and short tactile hairs, two campaniform domes, four olfactory pegs, and ten double-channelled gustatory hairs. This sensory array is suited to assess oviposition site resources, prior to and during the laying of an egg batch.
The tactile hairs and campaniform sensilla are each innervated by a single, tubular body containing dendrite. The olfactory pegs are each innervated by a single, moderately branched dendrite, which gains access to the external environment via pores at the bottom of deep grooves in the peg wall. The gustatory hairs fall into two categories. Four hairs have a single, tubular body containing dendrite at their base, and four unbranched dendrites running up to the hair tip which has a terminal pore. Six of the taste hairs have no tubular body containing dendrite at the base, and three unbranched dendrites running up to a terminal pore.     

Surface structures of the antenna of Mantophasmatodea (Insecta)

The cuticular fine structure of the antenna in Mantophasmatodea (Austrophasmatidae: Hemilobophasma montaguense, Austrophasma gansbaaiense) is described based on SEM images. The armature of sensilla (=s.) on the basiflagellum (14 basal flagellomeres, the distal ones of which are subdivided) and distiflagellum (7 distal flagellomeres) differs strongly. A basiflagellomere has a sporadic vestiture of prominent s. chaetica B as well as distal s. scolopidia and scattered s. coeloconica. The distiflagellum also bears scattered s. chaetica B and s. coeloconica but is also densely covered with sensilla of various other types: numerous s. trichodea and s. basiconica, sporadic s. coelocapitula, and a probably new type of branched sensilla; the distiflagellum is probably the main sensory region, including gustatory and olfactory chemoreception, mechanoreception, and hygroreception. The scape and pedicel also bear s. chaetica B, and s. chaetica A arranged in 4 (scape) or 2 (pedicel) hair-plates. Terminal s. campaniformia are only found on the pedicel. A ‘dark spot’ is present apically on distiflagellomeres 6 (as reported previously) and 1. The two spots are of similar structure and are possibly associated with glands; each comprises a complicated external aperture and a larger internal pouch enclosing a cavity; projections protrude from the pouch walls into the cavity. The surface structure of the basiflagellomeres shows differences that are possibly species specific. An overview is given on antennal apomorphies in Mantophasmatodea.     

Antennal sense organs of the cockroach, Leucophaea maderae

Adult and nymphal antennae of the cockroach, Leucophaea maderae, contain nine or more different morphological types of sense organs. There is no outwardly apparent sexual dimorphism in adult antennae. Nymphs are dificient in gross numbers of sensilla. Sense organs are classified morphologically by their similarity to known types of sensila and are assigned functions on this basis and preliminary electrophysiological data: Sensilla chaetica (A), thick-walled mechanoreceptive hairs in groups on the antennal base; S. chaetica (B), thick-walled setae which are tactile and probably chemoreceptive, occurring in the antennal base and flagellum; S. trichodea (A), thin-walled chemoreceptive hairs of the flagellum; S. trichodea (B), minute hairs on the scape and pedicel; S. basiconica, thin-walled chemoreceptive pegs, and S. coeloconica (?pit-pegs”?) of the flagellum; S. campaniformia and scolopidia, mechanoreceptors in the base and flagellum; plus Johnston's organ and/or connective chrodotonal organs in the pedicel. Calculations based on absolute counts of sensilla and their known innervation yield an estimate of about 3.3 × 10⁴ sensilla and 10⁵ cells per antenna.     

Antennal sensilla of triatominae (Hemiptera,Reduviidae): A comparative study of five genera

The paper analyses the antennal sensilla pattern of 22 species of triatomine bugs (Hemiptera, Reduviidae). The pedicels of species from tribe Rhodniini differ from species of Cavernicolini and Triatomini, mainly by the absence of trichoid and basiconic sensilla and by a greater number of Bristles I. Fifth-instar nymphs of T. sordida and R. pictipes show several differences in sensilla patterns compared with their respective adults. They lack basiconic sensilla and thin-and thick-walled trichoid sensilla over the first flagellar segment and over the proximal half of the second flagellar segment. T. sordida nymphs also lack these sensilla on the pedicel. There appears to be a significant sexual dimorphism in relation to trichoid sensilla in T. sordida, but not in R. pictipes. There exists a remarkable correlation between the density of basiconic and trichoid sensilla on the pedicels of different species, and a crude estimation of habitat range assessed as number of habitat types reported for each species.     

Gustatory organs of Drosophila melanogaster: fine structure and expression of the putative odorant-binding protein PBPRP2

In Drosophila, as in most insects, gustation is mediated by sensory hairs located on the external and internal parts of the proboscis and on the legs and wings. We describe in detail the organization and ultrastructure of the gustatory sensilla on the labellum and legs and the distribution of PBPRP2, a putative odorant-binding protein, in the gustatory organs of Drosophila. The labellum carries two kinds of sensilla: taste bristles and taste pegs. The former have the typical morphology of gustatory sensilla and can be further subdivided into three morphological subtypes, each with a stereotyped distribution and innervation. Taste pegs have a unique morphology and are innervated by two receptor cells: one mechanoreceptor and the other a putative chemoreceptor cell. PBPRP2 is abundantly expressed in all adult gustatory organs on labellum, legs, and wings and in the internal taste organs on the proboscis. In contrast to olfactory organs, where PBPRP2 is expressed in the epidermis, this protein is absent from the epidermis of labial palps and legs. In the taste bristles of the labellum and legs, PBPRP2 is localized in the crescent-shaped lumen of the sensilla, and not in the lumen where the dendrites of the gustatory neurons are found, making a function in stimulus transport unlikely in these sensilla. In contrast, PBPRP2 in peg sensilla is expressed in the inner sensillum-lymph cavity and is in contact with the dendrites. Thus, PBPRP2 could be involved as a carrier for hydrophobic ligands, e.g., bitter tastants, in these sensilla.     

Interactions of pheromone with moth antennae: Adsorption,desorption and transport

Isolated antennae of the male moth Antheraea polyphemus adsorbed at least 32% of ³H-labelled pheromone molecules (E-6,Z-11 hexadecadienyl acetate) from an airstream passing the antenna. About 80% of the adsorbed molecules were caught by the long olfactory hairs (sensilla trichodea). The distal half of the hairs caught about twice as many molecules as the proximal half. About 40% of the molecules desorbed if the antennae were exposed to a clean airstream for 30 min. The adsorbed molecules were transported from the hairs towards the antennal branch. Transport due to diffusion would have a diffusion coefficient of 3 × 10^?7 cm²/s. Forty per cent of the total radioactivity per hair could be detected in receptor lymph extruded from the olfactory hairs, after an incubation time of 2 min. Dried antennae showed an increased desorption and an increased velocity of the transport along the hairs. One interpretation is that the molecules enter the receptor lymph of the intact antennae and diffuse more slowly than those on the cuticular surface. Fractional elution of fresh antennae revealed a diminishing elutability of pheromone from antennae in pentane (DEP-effect) and almost constant elutability in more polar solvents (chloroform-methanol toluene). The DEP-effect could be reversibly abolished by dehydration of the antennae. It could be shown that the DEP-effect occurs mainly on the antennal branch rather than on the hairs. Residual (uneluted) radioactivity builds up mainly on the branch.     

一些蜘蛛类群味觉毛的形态、数量和分布

化学通讯是蜘蛛最基础和最普遍的种内及种间通讯方式之一,蜘蛛体表的味觉毛能够接触性地或者近距离地感知环境中的化学物质,但味觉毛的相关研究仅在少数几种蜘蛛中有过报道。我们通过扫描电镜分别对幽灵蛛科(Pholcidae)、弱蛛科(Leptonetidae)、泰莱蛛科(Telemidae)、蟹蛛科(Thomisidae)和球蛛科(Theridiidae)共5科32种蜘蛛味觉毛的形态、数量及分布进行了观察。结果显示:蜘蛛味觉毛一般呈"S"形或弧形;毛根部与体表形成较大角度,末端开口。一般分布在步足的跗节和后跗节,一些种类在步足胫节亦有味觉毛分布。所观察的蜘蛛中绝大部分种类在触肢上未发现味觉毛,仅有2种蟹蛛即角红蟹蛛(Thomisus labefactus)和膨胀微蟹蛛(Lysiteles inflatus)以及1种球蛛即鼬形微姬蛛(Phycosomamustelinum)在触肢上有味觉毛。味觉毛的数量在不同蜘蛛种类中有较大差异,从十几根到上百根不等。蜘蛛味觉毛的形态、数量和分布等特征除了与遗传相关外,亦有可能与其生境和生活方式等有关。     

Ultrastructure of the antennal sensilla of the mayfly Baetis rhodani (Pictet) (Ephemeroptera : Baetidae)

The distribution and fine morphology of antennal sensilla of nymphal and adult mayfly, Baetis rhodani (Ephemeroptera : Baetidae), were examined. In the nymph, various kinds of sensilla (chaetica, basiconica, coeloconica and cuticular pits) are differently arranged on the antennal segments, whereas sensilla campaniformia delimit the distal border of the pedicel. A peculiar kind of sensillum basiconicum, named flat-tipped sensillum, is present along the entire antenna, even though in the flagellum it has a regular arrangement between the cuticular lobes that delimit the distal border of each article. In the subimago the scape and pedicel are profusely covered with microtrichia and scattered sensilla trichodea, whereas the flagellum shows cuticular ribs. Sensilla coeloconica are present along the ventral side of the flagellum. In the imago, the antenna is completely decorated with scales among which sensilla trichodea and sensilla coeloconica occasionally occur. As in the nymph, adult mayflies have a ring of sensilla campaniformia along the distal border of the pedicel. When compared with nymphal antennae, those of adults have fewer types of sensilla, presumably in relation to the short, non-feeding terrestrial life.     

Antennal sensilla of whiteflies: Trialeurodes vaporariorum (Westwood), the glasshouse whitefly,and Aleyrodes proletella (Linnaeus), the cabbage whitefly, (Homoptera : Aleyrodidae). Part 2: Ultrastructure

A transmission electron microscope study of the antennal sensilla of the whitefly Trialeurodes vaporariorum and Aleyrodes proletella (Homoptera : Aleyrodidae) revealed that of the sensilla unique to the antennal flagellum (basiconic, coeloconic and small digitate-tipped sensory pegs), basiconic and coeloconic sensilla occur as subtypes. Four subtypes of basiconic cone sensilla occur on the flagella of T. vaporariorum and 3 on A. proletella. All the subtypes of basiconic sensilla have an ultrastructure typical of olfactory sensilla and probably have a primary olfactory function. Two subtypes of coeloconic sensilla occur on the flagella of both species. Their ultrastructure suggests primarily a chemosensory function. The digitate-tipped sensory peg of both species possesses a triad of neurones which have ultrastructural characteristics similar to the known thermo-/hygroreceptors of other insect species. The other sensilla, which occur on the antennae of the whiteflies, include cheatae, campaniform and subcuticular sensilla, all of which have an ultrastructure typical of mechanoreceptors.     

Antennal sensilla of the click beetle,limonius aeruginosus (OLIVIER) (COLEOPTERA: ELATERIDAE)

Antennal sensilla typology, number and distribution of the click beetle Limonius aeruginosus (Olivier) (Coleoptera: Elateridae) were studied using scanning electron microscopy. The serrate antennae of both sexes of L. aeruginosus consist of the scape, pedicel and of the flagellum which is composed of 9 flagellomeres. In both sexes, 5 types of sensilla basiconica, 1 type of sensilla trichodea, 1 type of sensilla chaetica, 1 type of sensilla campaniformia and Böhm sensilla were distinguished. No remarkable sexual differences in the types, numbers and distribution of sensilla were found on the antennae, except for the sensilla basiconica type II. The average number of sensilla basiconica type II on the antennae of the male beetle surpassed that on the antennae of the female beetle (3562 and 108 pegs, respectively). It is suggested that this type of sensilla on the male beetles antennae is responsible for the reception of the sex pheromone produced by the female beetle.     

Ultrastructure of sensilla on the antennal pedicel of the brown planthopper Nilaparvata lugens Stal (Insecta: Homoptera)

Scanning- and transmission electron-microscope studies of the sensilla of the pedicel of Nilaparvata lugens have revealed an elaborate plaque organ and three structurally different types of trichoid hairs. Each plaque organ is innervated by 120-150 neurons arranged in groups. The porous sensory cuticle is folded into finger-like projections and is surrounded by protective non-sensory denticles. Trichoid sensilla differ in number of neurons, appearance of dendrites and arrangement of pores. Type I, innervated by 2 neurons, has pores along its length and is probably olfactory in function. Types II and III are innervated by one and five neurons, respectively, and the absence of pores along the hair shaft indicates a possible gustatory role. The importance of these sensilla is discussed with reference to the behaviour of this important insect pest.     

Morphology of antennal sensilla of the brown spruce longhorn beetle,Tetropium fuscum (Fabr.) (Coleoptera: Cerambycidae)

The antennal sensilla of the brown spruce longhorn beetle, Tetropium fuscum (Fabr.) (Coleoptera: Cerambycidae) were examined with particular focus on the sensilla present on the apical flagellomere. T. fuscum antennae are composed of 11 segments, namely the scape, pedicel, and nine flagellomeres. Nine types of sensilla were observed: three types of sensilla chaetica, sensilla trichodea, two types of sensilla basiconica, grooved peg sensilla, thick-walled sensilla, and Böhm bristles. Seven of these types were present on the apical flagellomere, the exceptions were sensilla chaetica type 3 and Böhm bristles. There were no significant differences in the distribution or density of sensilla present on the ninth flagellomere of males and females, except that males had significantly more sensilla chaetica type 1, which are put forward as the putative contact chemoreceptors for T. fuscum.     

Digitiform Sensilla on the Maxillar Palp of Coleoptera

The fine structure of the digitiform sensilla on the distal segment of the maxillar palps of Tenebrio and Dermestes is described. Each sensillum is associated with a single sensory cell and three enveloping cells, which enclose two receptor lymph cavities. The inner receptor lymph cavity of both species shows a different structural feature. Branches of the outer dendritic segments, which contain numerous microtubules, run to the tip of the hairshaft. A dendritic sheath extends to the apex of the peg. The hairshaft possesses a second canal, which is free of dendrites. The poreless hairshaft is inserted in a cuticular canal; the longer distal part of the shaft is positioned in a narrow superficial groove. The digitiform sensilla do not show the typical structures of mechanosensitive sensilla. The absence of pores in the setal wall does not point to a function as olfactory or gustatory hairs. The presumed function of the sensilla is discussed in relation to thermo-, hygro- and CO₂-receptors.