Sensilla on the antennal flagellum of the sawyer beetles Monochamus notatus (Drury) and Monochamus scutellatus (Say) (Coleoptera: Cerambycidae)

The antennae of the sawyer beetles Monochamus notatus and M. scutellatus were examined with the light and scanning electron microscopes to determine the types, number, distribution and innervation of the sense organs. Nine types of sensilla are described. Both short, thin-walled pegs (sensilla basiconica) and reversely curved thick-walled hairs (sensilla trichodea) are chemoreceptors. There are three types of long, thick-walled hairs (sensilla chaetica) which may be mechanoreceptors. One of these is modified in males to form unique snail-shaped pegs. A few dome-shaped organs, probably campaniform sensilla, were found. In addition to sense organs, many glands occur in association with the sensilla, and the antennae are well supplied with dermal glands connected by canals to small pores on the surface.     

Ultrastructure of the funicular sensilla of the cabbage root fly,Delia radicum L. (Diptera : Anthomyiidae)

A transmission electron microscope study of the funicular sensilla of the cabbage root fly, Delia radicum, (Diptera : Anthomyiidae), showed 4 types of surface sensilla and 5 types of pit sensilla. The ultrastructure of the surface sensilla indicated all had a primary olfactory function. These include thick-walled multiporous trichoid sensilla, thin-walled multiporous basiconic sensilla (with 2 subtypes), thin-walled multiporous clavate sensilla, and grooved sensilla with channels at the base of each of the grooves. Clavate sensilla had 2 types of dendrites, one tubular, the other “scrolled”. This 2nd type may indicate an additional thermosensitive function. The dorsal pits contained thin-walled multiporous basiconic sensilla with a tapered tip. The ventral pits contain 3 types of sensilla, which have no wall pores and an inflexible socket. These may contain thermo- and/or hygroreceptors and include smooth-walled conical-, smooth-walled tapered- and striated pit sensilla. The 4th type is a grooved pit sensillum similar to the surface type.     

Morphology and distribution of sensilia on the cephalic appendages,tarsi and ovipositor of the European sunflower moth,Homoeosoma nebulella Den. & Schiff. (Lepidoptera : Pyralidae)

Sensilla on male and female antennae, mouthparts, tarsi and on the ovipositor of the European sunflower moth, Homoeosoma nebulella (Lepidoptera : Pyralidae) have been investigated by means of scanning electron microscope. The antennal flagellum bears multiporous sensilla (trichodea, basiconica, auricillica, coeloconica) and uniporous sensilla (chaetica, styloconica). A sexual dimorphism is found in the numbers of sensilla trichodea (8300 in males and 6000 in females) and sensilla basiconica (1150 in females and 650 in males). The proboscis has uniporous s. styloconica, multiporous s. basiconica (described for the first time in Lepidoptera), aporous s. chaetica, and some rare uniporous s. basiconica in the food channel. The labial palp-pit organ houses multiporous s. coeloconica, while the maxillary palps have aporous sensilla. Tarsi of both sexes possess one type of aporous s. chaetica and 2 types of uniporous s. chaetica. There is no significant difference in the distribution of tarsal sensilla between males and females. The surface of each lobe of the ovipositor is covered by 3 types of aporous s. trichodea of different lengths and about 60 multiporous s. basiconica, sensilla unusual on the ovipositor of Lepidoptera. The role of sensilla in the oviposition site selection is discussed.     

Ultrastructure of pheromone-detecting sensillum placodeum of the Japanese beetle, Popillia japonica Newmann (Coleoptera: Scarabaeidae)

The pheromone-detecting sensilla placodea are significantly more numerous than other sensory structures in the antennae of the Japanese beetle, Popillia japonica (Coleoptera: Scarabaeidae). Their abundance in males is nearly twice of that in females, showing a clear sexual dimorphism. Externally, they have a tortoise shell-like round cuticular plate containing a few polygonal plates separated by narrow ridges. Internally, they house two long dendrites that branch and terminate near fine cuticular pores. They have a system of two bipolar neurons accompanied by three enveloping cells, resembling sensilla trichodea in moths. The conspicuous difference with the latter is that the sensillum-lymph cavity near the outer cuticle is funnel-shaped, into which the tormogen cell projects numerous microvilli whose tips approach the terminal branches of the dendrites.     

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.     

Olfactory sensilla on the antenna and maxillary palp of the sheep head fly,Hydrotaea irritans (Fallen) (Diptera : Muscidae)

Antennae and maxillary palps of both sexes of the Sheep Head fly Hydrotaea irritans (Diptera : Muscidae) were investigated using scanning electron microscopy to describe the types, morphology, and distribution of olfactory sensory structures. Only socketed bristles and microtrichia were found on the scape of the antennae. These structures were also observed on the pedicel together with a group of 7–8 as yet undescribed sensilla, whose function is unknown. Olfactory sensilla were not found on these 2 segments or on the arista. Large numbers of olfactory sensilla and microtrichia were present on the funiculus. The former included sensilla trichodea (thick-walled, multiporous sensilla), sensilla styloconica and 6 types of sensilla basiconica (thin-walled, multiporous sensilla), 4 of which occurred individually and 2 of which were found in groups. An olfactory pit containing groups of thin-walled multiporous sensilla was located on the dorsomedian side of the funiculus. All sensilla basiconica were classified on morphological characteristics. The maxillary palps were covered with microtrichia and socketed bristles, but only 1 type of olfactory sensillum was found. This was a type of sensillum basiconicum that differed from any of those found on the antennae. No differences were found in sensilla diversity and distribution between males and females.     

Morphology and distribution of antennal sensilla of the tarnished plant bug,Lygus lineolaris (Palisot de beauvois) (Hemiptera: Miridae)

Sensilla on the antennae of adult and last-instar nymphs of the tarnished plant bug, Lygus lineolaris (Hemiptera: Miridae), were examined with light, scanning and transmission electron microscopy. Six different types were identified in adult females and males and 5 types in last-instar nymphs: types 1 and 4 are sensilla trichodea, 2 and 3 are sensilla chaetica, and 5 and 6 are sensilla basiconica. Type 1 are located at distal region of terminal segment and type 2 are located at distal regions of proximal 3 segments in both adults and nymphs. Type 3 is present on all segments, more numerous on scape and pedicel and less abundant on distal third and fourth segments in both adult and nymphal stages. Types 4 and 6 are absent on the scape and present on the distal 3 antennal segments in adults, but they are present only on the distal-most antennal segment in nymphs. Type 5 sensilla are present only on second antennal segments in adults and are absent in nymphs. Sexual dimorphism is observed in total numbers: there are significantly more type(s) 3, 4, 5 and 6 sensilla in adult males than adult females. Types 1, 4 and 5 are multiporous with thin cuticle, branched dendrites and pore tubules which suggests an olfactory function. These sensilla have 3, 3 and 2 neurons, respectively. The type 6 sensillum has an apical pore and pores in the cuticular wall, and is innervated by 5 nerve cells with unbranched dendrites. Sensillar types 2 and 3 have thick cuticle, a single apical pore and nerve cells with unbranched dendrites. Type 2 has 1 neuron and type 3 has 2 chambers and 2 nerve cells.     

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.     

Fine structure of tarsal sensilla of Aedes aegypti (L.) (Diptera: Culicidae)

The tarsi of all three pairs of legs of both sexes of Aedes aegypti (L.) bear spine sensilla, five types of hair sensilla, which are designated A, B, C1, C2 and C3, and campaniform sensilla. Type A and B hairs, spines, and cam-paniform sensilla are innervated by one neuron with a tubular body, a characteristic of cuticular mechanoreceptors. In particular the hairs and spines are tactile receptors and the campaniform sensilla are proprioceptors. The C1, C2, and C3 hair sensilla have the morphological features of contact chemoreceptors. Type C1 and C3 hairs are innervated by five and four neurons, respectively, which extend to the tip of the hair. Type C2 is innervated by five neurons, one of which terminates at the base of the hair in a tubular body while the remaining four extend to the tip of the hair. The role of the type C hairs in oviposition behavior, nectar feeding, and recognition of conspecific females is discussed. Presumed efferent neurosecretory fibers occur near the spine and hair sensilla.     

Fine structure of antennal mechanosensilla of adult Rhodnius prolixus stål (Hemiptera: Reduviidae)

Each antenna of both sexes of adult Rhodnius prolixus has approximately 570 mechanosensitive neurons that innervate five morphologic types of cuticular mechanosensilla: campaniform sensilla, tapered hairs, trichobothria, and type I and type II bristle sensilla. Each campaniform sensillum and tapered hair is presumably innervated by one mechanosensitive bipolar neuron and probably functions in proprioception. The campaniform sensilla being located at the base of the scape could monitor the position of the antenna. Tapered hairs are found at the distal margin of flagellar segment I and projecting laterally from the bases of the pedicel and scape. They probably provide information about the relative positions of the antennal segments. Seven trichobothrium are located on the pedicel and three on flagellar segment I. Each trichobothrium has a long filamentous hair inserted into the base of a socket that extends inwardly as a cuticular tube and is innervated by one bipolar neuron with a tublar body, a parallel arrangement of microtubules associated with electron-dense material. The trichobothria may respond to small variations in air currents. Type I bristles occur at the base of the antenna and are the most numerous type of mechanosensillum; an average of 452 occur on each antenna of females and 440 on males. The bristle is curved toward the antennal shaft and is serrated distally. Type II bristles are located distally and are the second most numerous type of mechanosensillum; an average of 88 were counted on each antenna of females and 94 on males. The type II bristle is straight with small, longitudinal, external grooves and projects laterally from the antennal shaft. Each type I and II bristle sensillum is innervated by a bipolar neuron whose dendrite is divided into an inner and outer segment. The outer segment is encased by a dendritic sheath which may be highly convoluted and distally contains a tubular body. Two sheath cells are associated with each sensillum. Both types of bristle sensilla have a tactile function. The tubular bodies of both types of bristle sensilla have a complex structure indicating that they are very sensitive. Variations in the amount and arrangement of the electron-dense material at the tip of the tubular bodies may reflect differences in viscoelastic properties that underlie functional characteristics.     

A scanning electron microscopic survey of the cuticle in Cyphophthalmi (Arachnida, Opiliones) with the description of novel sensory and glandular structures

The cuticular surfaces of Cyphophthalmi (Opiliones) were studied in detail, covering a wide range of their taxonomic diversity. Previously unknown structures are described, including a sexually dimorphic row of spines and glandular openings on leg I of Fangensis cavernarum. Scanning electron micrographs of the prosomal paired hairs and the subapical process are provided for the first time. Evidence for the multi-pored nature of the shaft of solenidia as well as the hollowed nature and absence of wall pores of sensilla chaetica are also shown for the first time using scanning electron microscopy. The prosomal paired hairs may constitute a novel autapomorphy for Cyphophthalmi, as they are absent in all studied members of the other species of Opiliones. Finally, the variation in shape of some of the structures examined may be of great taxonomic value.     

Response of <Emphasis Type="Italic">Trichogramma chilonis</Emphasis> to infochemicals: an SEM and electrophysiological investigation

The external morphology and peripheral olfactory responses of antennal chemoreceptors of Trichogramma chilonis Ishii (Hymenoptera:Trichogrammatidae) to host related stimuli were examined by SEM and EAG technique respectively. The antennae of male and female T. chilonis reveal strong sexual dimorphism in structure as well as in types, density and distribution of individual sensillar types. The female antennae are characterized by the presence of a single uniporous sensilla on the apical tip of the dome and numerous multiporous pitted sensilla. Sensilla common to both males and females include the multiporous plate sensilla, the peg sensilla and trichoid sensilla. Differences between males and females occur with respect to their EAG profiles to 22 chemicals commonly found in plants viz., hexanal, -pinene, citronellal, terpinene, citronellol, phytol, caryophyllene, R-(+)-limonene, linalool, carvacrol, cis-3-hexen-1-ol, ethanol, -pinene, trans-2-hexanal, -phellandrene, amyl acetate, cineole, quinolene, S-(–)limonene, -myrcene, carvone, terpineol; hexane leaf extracts of three host plants of Helicoverpa armigera (cotton, chickpea and pigeon pea) and hexane scale extracts of adult males and females of H. armigera. Individually, the largest peak amplitudes in females were obtained with citronellal, phytol, caryophyllene, R-(+)-limonene, linalool, carvacrol and citronellol while in males citronellol, caryophyllene, linalool, R-(+)-limonene and amyl acetate caused the highest response. Among the different chemical classes, the largest peak amplitudes in females were obtained with oxygenated monoterpenes, while in males, fatty acid derivatives caused the highest response. In both males and females, the hydrocarbon monoterpenes caused the least response. Thus, the wide spectrum response of Trichogramma chilonis, to a wide group of chemicals belonging to different chemical classes, though varying, nevertheless suggests that using plant information enhances its parasitization efficiency.     

伪鞘榕小蜂雌雄成虫触角感器的超微形态、分布及适生意义

伪鞘榕小蜂Sycoscapter trifemmensis是一种寄生于鸡嗉子榕间花期榕果的专性寄生蜂,雌雄两性繁殖策略分化明显,为更好理解和诠释雌蜂寄主定位和雄蜂配偶识别机制,有必要对两性的触角感器进行观察。运用环境扫描电镜观察,对比和探讨了伪鞘榕小蜂雌雄成虫的触角和触角感器类型、分布、数量及其生态适应性。结果表明:雌蜂触角鞭节由11鞭小节组成,总长817.82±33.23μm,分布有毛形感器、刺形感器(类型1)、锥形感器(类型1)、多孔板形感器(类型1)、栓锥形乳突状感器5类5种;雄蜂触角鞭节仅由6鞭小节组成,全长为雌蜂的1/3,且各节有明显的缩短和增粗特征,着生感器包括毛形感器、刺形感器(类型2和类型3)、锥形感器(类型1和类型2)、多孔板形感器(类型2)、腔锥形感器5类7种。雌蜂触角感器的数量与分布显著高于雄蜂,且同类型感器在雌蜂上具有明显的延伸、增粗、分支的特征,以板形感器和锥形感器最为突出。伪鞘榕小蜂雌雄成虫的触角及其感器有明显的性二型,特别是与化学信息识别相关的感器,反映了雌雄蜂在不同生态环境和繁殖压力下的形态分化、行为策略和生态适应。     

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.     

Antennal sensilla in five Psychodini moth flies (Diptera: Psychodidae: Psychodinae) pollinators of Arum spp. (Araceae)

The pollination of the genus Arum (Araceae) is mainly achieved by deception, the floral odour mimicking the pollinator ovipositing site. In order to discover the sensory organs involved in this attraction, we have studied the antennae of five species of psychodine moth-flies (former Psychoda sensu lato=Psychodini), pollinators of Arum spp. The antennae of the five Psychodini reveal seven types of sensilla: multiporous tribranched sensilla basiconica (sensilla ascoidea), multiporous sensilla basiconica, multiporous sensilla coeloconica, multiporous sensilla auricillica, uniporous sensilla basiconica, aporous sensilla chaetica, aporous Böhm’s sensilla. Each species possesses three, five or six of these sensillum types. All the multiporous sensilla are probably olfactory receptors while the uniporous sensilla basiconica must possess a contact chemoreceptive function. The multiporous tribranched sensilla basiconica (s. ascoidea), present in all the species, are the best candidates for the reception of the odours given off by the ovipositing sites and the inflorescences of Arum. The multiporous sensilla basiconica and the multiporous sensilla coeloconica may be involved respectively as CO₂ receptors or thermoreceptors. Psychoda phalaenoides, which is the main pollinator of A. maculatum, is the species which possesses the largest number of antennal sensilla. The sexual dimorphism, studied only in Psycha grisescens, as concerns the number of sensilla and the absence of a sensillum type which differ according to sex, is difficult to interpret.     

Structure and function of antennal pore plate sensilla of oryctes rhinoceros (L.) (Coleoptera : Dynastidae)

The antennae of the rhinoceros beetle, Oryctes rhinoceros (Coleoptera : Dynastidae), comprise 4 parts : the scape, the pedicel, a funicle, and a club of 3 lamellate segments. The inner surfaces of the lamellate club segments carry one type of trichoid sensilla, 2 types of sensilla coeloconica, and 3 types of multiporous pore plate sensilla. The total surface occupied by the sensilla on the antenna is 5.2±0.4 mm² in males (mean±SD) and 5.4±0.5 mm² in females. With a measured density of 8665±1254 sensilla per mm² in males and 8952±1642 sensilla per mm² in females, the total number of pore plate sensilla was estimated to be between 45,000 and 50,000. The structure of the 3 types of pore plate sensilla is described. SP1 are the most abundant type of placoid sensilla. They show a convex and rugged plate whose infoldings form a circle of irregular cavities. SP2 sensilla are characterised by a smooth and convex plate, surrounded by a furrow with a ridge. SP2 are localised on a wide band situated along the straight side of the lamella. The plate of SP3 is nearly flat and there is no furrow. SP3 are confined within a narrow margin along the convex edge of lamellae. The 3 types of pore plate sensilla house 2 neurones whose dendrites branch repeatedly under a plate of thin (0.2 μm) cuticle, which is pitted with numerous pores, 40 nm in diameter. Single sensillum recordings with tungsten microelectrodes revealed the firing activity of 2 neurones. These receptor neurones responded specifically to olfactory stimulus. Olfactory receptor neurones tuned to the male pheromone compound, ethyl 4-methyl octanoate, were found in male and female antennae. Other receptor neurones responded to plant volatiles. Morphological and electrophysiological data suggest the absence of a sexual dimorphism in the olfactory organs. The functional organisation of the olfactory organs is discussed in terms of their adaptation to the ecology of O. rhinoceros.     

Sensory receptors on the adult labial and maxillary palpi and galea of Cicindela sexguttata (Coleoptera: Cicindelidae)

Five types of sensilla are situated on the apical area of the labial and maxillary palpi and galea of Cicidela sexguttata. Large, conical, and peg-like sensilla are in rows on the central region of each palpus. These sensilla have a hollow cuticular peg, with an apical pore and multi-innervation. This central region of palpal sensilla is surrounded by campaniform sensilla that are disc-shaped and small conical peg sensilla. A similar type of conical sensillum as the found in the palpal central region is situated around the periphery of the palpal apex and apex of the galea. This conical peg sensillum is located in a shallow depression and is structurally similar to the other peg sensilla, but it has a mechanoreceptor neuron attached to the cuticular base of the sensillum. A long, single, trichoid sensillum is situated in the center of the galea and is hollow, thick-walled, porous, and multi-innervated. The apices of the palpi and galea have a large number of dermal gland openings that actively secrete a substance during the feeding process of the tiger beetle. © 1995 Wiley-Liss, Inc.     

External morphology of antennae and their sense organs in the roach Gromphadorhina brunneri (Blattoidea: Dictyoptera)

The antennae and their sense organs in nymphs and adult roaches of Gromphadorhina brunneri, were investigated and described. The number of segments and sensillae of the nymphal antennae depend on the developmental stage. Sexual dimorphism is pronounced. Males have longer antennae than females as well as an abundance of especially long sensory hairs (long wavy hairs), which are probably responsible for the perception of female sex pheromones. They also have more thin-walled sensory hairs, for instance, sensilla trichodea. On a morphological basis the sensillae of Gromphadorhina brunneri, were named and classified. Long wavy hairs and large sensory hairs appear to be present also in a related species, G. portentosa, but are lacking in others. Their distribution on the antennae varies greatly from that in G. portentosa but their structure varies only slightly. These two types of sense organs are considered to be specialized forms of sensilla chaetica. They are contact chemoreceptors, as are two other types of sensilla chaetica. Furthermore, thin-walled chemoreceptors are present, such as sensilla trichodea, sensilla basiconica, sensilla coeloconica and a typical mechanoreceptor, the sensillum campaniformium.     

Morphology,ultrastructure and functional role of antennal sensilla in off-host aggregation by the bed bug,Cimex lectularius

After blood feeding on a host, bed bugs, Cimex lectularius, assemble in aggregation sites away from the host. Off-host aggregation is mediated by a combination of mechanical and chemical stimuli associated with bug feces. Partial antennectomies indicated removal of flagellomeres did not affect aggregation, but removal of the whole pedicel or its distal half significantly reduced (P < 0.01) aggregation, suggesting that sensilla related to off-host aggregation occur on the distal half of the pedicel. Scanning electron microscopy (SEM) revealed that serrated hairs were distributed throughout the pedicel, but newly described smooth hairs were present mainly on the distal half, and a distinct patch of grooved pegs, smooth pegs and immersed cones was present on the posterior edge of the distal half of the pedicel in adults, but not in nymphs. Numbers of different types of sensilla increased significantly during metamorphosis from first instar to adult (P < 0.05), but were similar between genders (P = 0.11) and between females from a laboratory and field strain of bugs (P = 0.19). Transmission electron microscopy (TEM) revealed that cuticular pores were present in the two types of pegs, indicating that the pegs have an olfactory function. The smooth hairs resembled gustatory sensilla previously described in Cimex hemipterus F. The existence of both olfactory and gustatory sensilla on the distal half of the pedicel suggests those sensilla may be the sensory basis of off-host aggregation behavior.     

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.