Ultrastructure and ontogeny of the hair sensilla on the funicle of Calliphora erythrocephala (Insecta,Diptera)

Summary Four envelope cells are responsible for the formation of the basiconical sensilla of Calliphora. They are the thecogen, trichogen, and tormogen cells, and envelope cell 4. In early stages of development the still subepithelial sensory cilia are completely enclosed by the innermost thecogen cell. The first formation movements are initiated by a growth thrust of the hair-forming cell into the exuvial space. The sensory cilia only begin to grow into the hair anlage when the hair-forming cell has almost reached its final length. As soon as growth is completed the trichogen cell, tormogen cell, and envelope cell 4 start to excrete cuticular material. The trichogen cell forms the perforated part of the hair shaft and the stimulus-conducting system consisting of the pore tubules. The tormogen cell is responsible for the excretion of the basal non-perforated hair shaft and sheath cell 4 forms the proximal part of the socket region. The thecogen cell only begin to produce dendritic sheath material when the sensory hair is almost complete.Approximately 7–8 days after pupation the tormogen cell degenerates, having, by this time, produced about two-thirds of the sensilla cuticle. The surrounding envelope cells incorporate cell fragments of the tormogen cell. The trichogen cell continues the secretion where the tormogen cell left off. When the secretion of cuticle is finished the sheath cells begin to withdraw towards the proximal direction and to form microvilli on the apical membrane. The resulting outer receptor lymph space is bordered by envelope cell 4 and the trichogen and thecogen cells. The tormogen cell is absent in the sensilla of the imago.Abbreviations DS dendritic sheath - E4 envelope cell 4 - Ex exuvial space - G glial cell - iD inner dendritic segment - iRL inner receptor lymph space - oRL outer receptor lymph space - oD outer dendritic segment - P pore - PT pore tubules - S sensory cell - T thecogen cell - TO tormogen cell - TR trichogen cell Part 1 of a dissertation accepted by the Faculty of Bio- and Geosciences, University of Karlsruhe     

Ultrastructure des sensilles trochanteriens de Campodea sensillifera conde et mathieu (Diplura : Campodeidea)

The fine structure of the basiconica sensilla situated on the posterior part of trochanters in Campodea sensillifera (Diplura : Campodeidea) reveals that they are probably olfactory and mechano-sensitive setae. Each sensillum is composed of one sensory axis made of 3 dendrites ensheathed by 3 cells (thecogen, trichogen and tormogen); one outer segment ends by a tubular corper without connection with the cuticular layer. The setae are generally racket-shaped. The epicuticular layer of the expanded part is perforated by a lattice of numerous slits, which communicate with underlying canals. The ciliary structures and apex of the tormogen cell are eliminated just before ecdysis. The ciliary microtubules are present in the cavity of the new sensillum, but after ecdysis the microtubules persist only at the lower part of the peduncle. An ecdysial canal appears at the tip of the sensillum.     

Ultrastructure of the chemosensitive basiconic single-walled wall-pore sensilla on the antennae in adults and embryonic stages of Locusta migratoria L. (Insecta,Orthoptera)

Summary The structure and embryonic development of the two types (A, B) of basiconic sensilla on the antennae of Locusta migratoria were studied in material that had been cryofixed and freeze-substituted, or chemically fixed and dehydrated. Both types are single-walled wall-pore sensilla. Type-A sensilla comprise 20–30 sensory and 7 enveloping cells. One enveloping cell (thecogen cell secretes the dendrite sheath); four are trichogen cells, projections of which form the trichogen process during the 2nd embryonic molt. The trichogen cells form two concentric pairs proximally. Two tormogen cells secrete the cuticular socket of the sensillum. The dendritic outer segments of the sensory cells are branched. Bifurcate type-A sensilla have also been observed. Type-B sensilla comprise three sensory and four enveloping cells (one thecogen, two trichogen and one tormogen). The trichogen process is formed by the two trichogen cells, each of which gives rise to two projections. The trichogen cells are concentrically arranged. The dendritic outer segments of the sensory cells are unbranched. In the fully developed sensillum, all trichogen and tormogen cells border on the outer receptor lymph cavity. It is suggested that the multicellular organization of the type-A sensilla can be regarded as being advanced rather than primitive.Supported by the Dcutschc Forschungsgemeinschaft (SFB 4/G1)     

Etude infrastructurale de la stipule de Vicia faba L. au niveau du nectaire

Summary In the extrafloral nectary of the broad bean there is evidence of two fundamental types of cells: one with dense hyaloplasm, well developed ergastoplasm and golgi apparatus, all features of glandular cells, and another with opposite features. The cells of the head of the secretory hairs and those of the subjacent epidermis which are not prolonged with such a hair are of the first type. The epidermal cells prolonged with a hair and the pedicellar cell of this hair are of the second type. Moreover, the companion cells of the subjacent conducting bundle look like cells of the first type, especially those of the head of the secretory hairs owing to their numerous wall protuberances. Cells of the second type are presumably involved in transit processes between phloem and trichome, and cells of the first type in excretory processes.

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Ce travail fait partie d'une Thèse de Doctorat d'Etat sur la cyto-physiologie des nectaires. — (Travail effectué au Laboratoire de Bot. Appl. et Microbiologie et au Centre de Microscopie électronique de la Faculté des Sciences de Bordeaux (France).     

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。     

Birds as predators of the pine processionary moth (Lepidoptera: Notodontidae)

The beneficial role of insectivorous birds potentially contributing to the biological control of forest insect pests appears crucial in the context of climate warming, especially for species currently expanding their range such as the pine processionary moth Thaumetopoea pityocampa. Larvae of T. pityocampa are aposematic and carry true urticating setae which, together with overwintering in silk winter nests, prevent them from predation by most insectivorous forest birds. The present review aims at pointing out which bird species can regularly feed on this key forest defoliator throughout its distribution range, and which predation strategies allow birds to cope with the urticating setae carried by late-instar larvae. At least seven bird species can be considered as regular predators of the pine processionary moth: four large migrant specialists (great spotted cuckoo Clamator glandarius, common cuckoo Cuculus canorus, European nightjar Caprimulgus europaeus and Eurasian hoopoe Upupa epops) and three small sedentary generalists (great tit Parus major, crested tit Lophophanes cristatus and coal tit Periparus ater). Each species has developed morphological traits and foraging techniques to feed on different life stages of T. pityocampa throughout the year: (i) gizzard wall structure allowing the consumption of caterpillars with urticating setae (cuckoos); (ii) nocturnal foraging on moth imagos by aerial hawking (nightjars); (iii) ground probing on below-ground pupae with long curved bill (hoopoe); and (iv) shifted predation period in autumn and winter on eggs, early- and late-instar larvae, with particular feeding technique allowing to eat only the inner parts of urticating larvae stages (tits). Although several avian predators regularly feed on T. pityocampa, only a few specialist and generalist insectivorous birds may contribute to regulate its populations, especially when population density of the moth is low. Moreover, their efficiency may possibly be threatened by mismatches associated with climate change.     

The development of taste and tactile hairs in the pharate fly Protophormia terraenovae (Diptera,Calliphoridae) and in the embryonal cricket Acheta domestica (Orthopteroidea,Ensifera)

Summary 1. The development of taste hairs and tactile hairs of the fly Protophormia terraenovae is described using light microscope, scanning, and transmission electron microscope methods.2. The development of taste hairs proceeds in the same way on tarsi, labella, and wings. First the dendritic outer segments of ciliary origin become visible above the hypodermal cell surface [2 days after pupariation (AP) at 19° C]; then the dendritic sheath starts growing out and finally the trichogen process follows. In a typical intermediate stage (stage C) the distal sections of the dendrites float freely in the fluid surrounding the pharate adult. The more proximal sections are enclosed by the dendritic sheath around which the trichogen process is wrapped (4 days AP). The protruding dendrites disappear when the cuticle starts being deposited on the fully grown trichogen process, and the sheath vanishes later (9–10 days AP or 1 day before eclosion). The development is discussed with respect to the known structural organization of the adult hair.3. In the tactile hairs the single dendrite which grows outwards is completely covered by the dendritic sheath and lies beside the trichogen process [stage C(m)].4. The taste and tactile hair development proceeds in the same way on legs isolated from the pupa after disc eversion in an artificial medium containing ecdysterone.5. To check that both these patterns of development are widespread the development of taste and tactile hairs of the first instar cercus of the cricket Acheta domestica was studied with the light microscope: Both hair types pass through identical early stages.     

Morphogenesis of the antenna of the male silkmoth. Antheraea polyphemus, III. Development of olfactory sensilla and the properties of hair-forming cells

During adult development of the male silkmoth Antheraea polyphemus, the anlagen of olfactory sensilla arise within the first 2 days post-apolysis in the antennal epidermis (stage 1-3). Approximately on the second day, the primary dendrites as well as the axons grow out from the sensory neurons (stage 4). The trichogen cells start to grow apical processes approximately on the third day, and these hair-forming 'sprouts' reach their definite length around the ninth day (stages 5-6). Then the secretion of cuticle begins, the cuticulin layer having formed on day 10 (stage 7a). The primary dendrites are shed, the inner dendritic segments as well as the thecogen cells retract from the prospective hair bases, and the inner tormogen cells degenerate around days 10/11 (stage 7b). The hair shafts of the basiconic sensilla are completed around days 12/13 (stage 7c), and those of the trichoid sensilla around days 14/15 (stage 7d). The trichogen sprouts retract from the hairs after having finished cuticle formation, and the outer dendritic segments grow out into the hairs: in the basiconic sensilla directly through, and in the trichoid sensilla alongside, the sprouts. The trichogen sprouts contain numerous parallel-running microtubules. Besides their cytoskeletal function, these are most probably involved in the transport of membrane vesicles. During the phase of cuticle deposition, large numbers of vesicles are transported anterogradely from the cell bodies into the sprouts, where they fuse with the apical cell membrane and release their electron-dense contents (most probably cuticle precursors) to the outside. As the cuticle grows in thickness, the surface area of the sprouts is reduced by endocytosis of coated vesicles. When finally the sprouts retract from the completed hairs, the number of endocytotic vesicles is further increased and numerous membrane cisterns seem to be transported retrogradely along the microtubules to the cell bodies. Here the membrane material will most probably be used again in the formation of the sensillum lymph cavities. Thus, the trichogen cells are characterized by an intensive membrane recycling. The sensillum lymph cavities develop between days 16-20 (stage 8), mainly via apical invaginations of the trichogen cells. The imago emerges on day 21.     

Three odorant-binding proteins are co-expressed in sensilla trichodea of Drosophila melanogaster

Odorant-binding proteins (OBPs) are small soluble proteins present in the aqueous medium surrounding olfactory receptor neurones. In this study we examine the expression patterns of three Drosophila OBPs (LUSH=OBP76a, OS-E=OBP83b and OS-F=OBP83a), using post-embedding immunocytochemistry. All three OBPs are co-expressed in sensilla trichodea whereas sensilla intermedia show co-expression of OS-E and OS-F only, but not of LUSH. Thus, it is confirmed that an individual sensillum can contain more than one OBP, even if it comprises only a single receptor neurone, such as the subtype T-1. In s. trichodea of lush⁻ mutants, expression of OS-E and OS-F is not impaired. No other sensillum type on antenna or maxillary palp (e.g. sensilla basiconica, sensilla coeloconica) expresses LUSH, OS-E or OS-F. Within the s. trichodea the three OBPs show the same labelling pattern: the extracellular sensillum lymph in the hair lumen and the sensillum-lymph cavities are heavily labelled. Intracellularly, the three OBPs are co-localised in a variety of dense granules in all auxiliary cells, and also in the receptor neurones. Immunocytochemical data from antennal sections of flies where lush gene expression has been tagged with the reporter gene lacZ suggest that LUSH is synthesised only in the trichogen and the thecogen cells. Thus, LUSH OBP is produced and secreted by two auxiliary cells, whereas its turnover and decomposition does not appear to be restricted to these auxiliary cells but may also occur in the tormogen and receptor cells. The immunocytochemical results are discussed with respect to current concepts of the function of odorant-binding proteins.     

Structure of isolated sensilla and sensory neurons in vitro: Observations on developing silkmoth antennae

Summary By combined enzymatic and mechanical treatment, it was possible to dissociate the sensory epithelium of developing antennae of male Antheraea polyphemus and A. pernyi silkmoths from the stage of separation of the antennal branches up to the early stages of cuticle deposition. Large numbers of entire developing trichoid sensilla were isolated. These are characterized by a large trichogen cell with a long apical, hair-forming process and a large nucleus. A cluster of 2–3 sensory neurons, enclosed by the thecogen cell, is situated in the basal region. The dendrites run past the nucleus of the trichogen cell into the apical process from which they protrude laterally. The nuclei of the tormogen and a 4^th enveloping cell can be distinguished near the base of the prospective hair. After further dissociation, only the neuron clusters remain, still enclosed by their thecogen cell and often attached to the antennal branch nerve via their axons. It is finally possible to disrupt the thecogen cells and the axons, leaving the sensory neurons with inner dendritic segments and axon stumps. The majority of these neurons can be expected to be olfactory.     

Hair regeneration in a solfugid chemotactile sensillum during moulting (Arachnida: Solifugae)

Summary The hair regeneration of a chemotactile sensillum was studied in the sunspiderGluvia during moulting. The sensilla in the old cuticle remain connected to the epidermis by dendrites which extend outwards during apolysis. The trichogen cells forming the new hairshaft in the exuvial space grow along the chemoreceptive dendrites, while the mechanoreceptive dendrites run separately. Morphogenetic aspects are discussed in comparison to results from other arthropods.     

Thaumetopoein, an urticating protein of the processionary hairs of the caterpillar (Thaumetopoea pityocampa Schiff) (Lepidoptera, Thaumetopoeidae)

The irritating fraction extracted from processionary caterpillar hairs contains soluble proteins which were separated by various electrophoretic and immuno-electrophoretic techniques. Some of these proteins are present also in cuticle and haemolymph. One protein of 28,000 daltons, formed of two subunits (13,000 and 15,000 daltons) is hair specific and causes a reaction in pig skin identical to that produced by hair extract. It is therefore an urticating protein and which we have named "Thaumetopoein".     

Embryonic development and molting of the antennal coeloconic no pore- and double-walled wall pore sensilla in Locusta migratoria (Insecta,Orthopteroidea)

Summary The embryonic development of antennal coeloconic sensilla was studied at four stages between 132 and 252 h after oviposition in Locusta migratoria. Initially the anlagen of the sensilla consist of 2–4 sensory cells and 3 enveloping cells. Two additional cells contribute later to the formation of socket and pit. The dendritic outer segments of the sensory cells elongate before the trichogen process grows out (ecdysis type I) with exception of one sensory cell in anlagen of poreless (np) sensilla. Other differences between np and double-walled wall pore (dw wp) sensilla are not visible until at least about 220 h after oviposition. Molting, which was studied in four stages, follows ecdysis type I in both sensillum types. The fourth enveloping cell maintains its tight connection to the socket of the sensillum even after apolysis. Its apical portion is torn off and shed together with the old cuticle. The electron-dense material between the dendritic sheath and the cuticular wall of the peg in np sensilla, which is regarded important for stimulus transmission, is not deposited during retraction of the trichogen cell. The concentric walls and spoke channels characteristic of dw wp sensilla result from deposition of cuticular material around wedge-shaped projections of the trichogen cell. The typical trilaminar 15 nm cuticulin layer is produced only on the ridges of these sensilla. The first cuticular lining of the spoke channels is only 7 nm thick and of a different structure. A flocculent material surrounds the outgrowing trichogen process. It is continuous with the filling of the spoke channels and can thus be considered as component of the stimulus-transmitting material in the functioning intermolt dw wp sensilla.     

Development of the hair mechanosensilla on the pupal labial palp of the butterfly,Pieris rapae L. (Lepidoptera : Pieridae)

Structure and ontogeny of the hair mechanosensilla on the distal segment of the pupal labial palp of Pieris rapae (Lepidoptera : Pieridae) were investigated in 7 successive stages between 28 hr after pupation and emergence of the imago. There are 7–8 mechanosensilla in the distal region of each palp in both sexes. These sensilla house a single sensory cell characterized by a tubular body, and 3 enveloping cells.At 28 hr after pupation, the anlagen of the hair mechanosensila are visible. Consecutive steps in the formation of the sensilla are: (1) elongation of the outer dendritic segment and of the dendritic sheath; (2) outgrowth of the trichogen cell and cuticle deposition; (3) increase in the diameter of the dendritic outer segment and in the number of microtubules within it; (4) reduction of the distal part of the dendritic outer segment and formation of the tubular body; (5) folding of the membrane of the dendritic outer segment and appearance of the receptor lymph cavity.The tubular body is formed during a period of about 80 hr. Its earliest appearance comprises groups of 3–4 microtubules, which are connected by electron-dense material. The final dense tubular body develops via microtubules linked together by electron-dense material.     

The structure and development of the hairpencil glands in males of the queen butterfly, Danaus gilippus berenice

Queen butterflies do not mate until the male has brushed the tufts of his scented, abdominal ”?hairpencils? over the female's head and antennae. The trichogen cells located at the base of each hairpencil are secretory. Presumably, these cells produce the sex pheromone necessary for mating. The liquid secretion must move from a central, microvillus-lined vesicle through the cuticle of the hairs to coat numerous, free, cuticular ?dust”? particles which adhere to the hairs' surface. The dust carries the secretion to or near the female's antennae. In the pupal stage the dust particles develop as outpocketings of the hair epicuticle. An amorphous matrix, probably protein epicuticle, is deposited in the outpocketings between the cuticulin layer and plasma membrane of the hair. Before the butterfly emerges from the pupa the matrix becomes enclosed by cuticulin, and the particles pinch off from the hair.     

Morphology and ontogeny of single-walled multiporous sensilla of hemimetabolous insects

Comparative morphological investigations were made to determine the common organization plan of single-walled multiporous sensilla. The development of multiporous chemoreceptive sensilla of Gryllus, Oncopeltus and Lepisma follows the same path. Each chemoreceptive sensillum is associated with four types of enveloping cell. During ontogeny, enveloping cell 1 secretes the dendritic sheath. Enveloping cell 4 builds the connection of the hair base with the antennal cuticle. In Gryllus and Oncopehus, enveloping cells 2 and 3 build the hair shaft, the wall pores and pore tubules in nearly equal parts. Enveloping cells 2 and 3 lie side by side in the hair process, in which enveloping cell 2 produces the inner part, enveloping cell 3 the outer part of the hair shaft. In Lepisma the predominant part of the hair shaft with the wall pores is formed by the doubled enveloping cells 3. Interpreting our findings and the literature data, a new proposal is given for the homology of the enveloping cells. In singlewalled chemoreceptors, enveloping cell 1 is considered as thecogen and enveloping cell 4 as tormogen cell. Enveloping cell 2 is interpreted as inner trichogcn cell and enveloping cell 3 as outer trichogen cell.     

Das Puffmuster der Borstenapparat-Chromosomen vonSarcophaga barbata

The chromosome complement ofSarcophaga barbata polytene scutellar trichogen and tormogen cells is described and the puffing sequences of chromosome IV were analysed from day 5 to day 17 of pupariation, i. e. from the beginning up to the end of bristle and socket formation at 21°C. There are 5 normal polytene chromosomes and a complex of fibrillar and granular heterochromatin in the giant cell nuclei. It is supposed that the heterochromatic masses represent the underreplicaetd sex-chromosomes. During a 13 day period of development 105 puffs appear in the trichogen cell chromosome IV respective 102 puffs in the tormogen cell chromosome IV. The puffing patterns of these two sister cells show many similarities. However, according to the differences in development, morphology and function of bristle and socket, there are also specific differences in the puffing patterns of the trichogen and tormogen cell. Preliminary observation suggest that the hormone bursicon induces some new puffs in the tormogen cell chromosomes of freshly emerged adults.     

Development of the male scent organ ofCreatonotos transiens (Lepidoptera,Arctiidae) during metamorphosis

Summary (1) The male abdominal scent organ (corema) of the arctiid mothCreatonotos transiens consists of a basal bladder and four tubes. It can be everted from the sternal intersegmental membrane 7/8. Its scent hairs (scales) produce and release the pheromone hydroxydanaidal, which attracts both sexes. Pyrrolizidine alkaloids (PA) ingested by the larva with its food are not only precursors of the pheromone but also a morphogen, which quantitatively controls the growth of the pupal corema and, thus, its final size and number of hairs. (2) The coremata arise from epidermalanlagen at the anterior border of the 8th abdominal sternite. If male larvae are fed 1 mg PA these organs begin to develop from small vesicles, and four tubes then arise during the first 3 pupal days. The corresponding mitoses reach their peak at 36 h. During the next 2 days the tubes shorten, while the walls become thin and doubly folded. The total surface of the corema increases about 20 times because of the shape transformation of the epidermal cells from prismatic to very flat. (3) The scent hairs originate from trichogen cells, which arise together with their associated tormogen cells during the 1st pupal day by way of differential mitoses. As the trichogen cells grow, their nuclei enlarge by way of endomitoses, elongate distally, and thus produce the hairs that extend into the lumen of the corema. Tormogen cells degenerate by the 8th day at latest. The hairs in each tube form a thick, caudally oriented bundle. The hair cells are finally bottle-shaped and at day 6 they extend freely into the hemolymph space. They are probably also the pheromoneproducing cells in later pupal and early imaginal life. Mitoses that produce trichogen cells stop after the 1st day, those producing epithelial cells 2 days later. This delay shifts the ratio of the two cell types from about 111 (18 h) to 140. (4) The processes hitherto described refer to normogenesis with ample PA supply. Control coremata in PA-free or PA-deficient specimens develop in principle in the same way, but at a slower rate, with minimal hair cell numbers barely 1/10th of normal, or at any rates between, depending upon the earlier PA supply. The size of control coremata varies from very small to small; even the hair cells and the hairs are smaller. (5) PA regulates corema development quantitatively through the number of mitoses of its cells and of endomitotic steps of the hair cells. In PA-treated specimens the coremaanlage is already advanced prior to pupation, at about the time when its sensitivity to PA influence terminates, in the early prepupa. Since PA only affects the anlagen of the corema and not that of any other body part (not even the basal coremal bladder), we postulate a selective interaction of PA with the presumptive corema cells. We found earlier that ecdysone is also involved, since the respective cell numbers can only be realized if this hormone is present.     

Ultrastructure of sensillum t1 on the foretarsus of Acerentomon majus berlese (Protura : Acerentomidae)

The shape and ultrastructure of sensillum t₁ on the foretarsus of the proturan, Acerentomon majus Berlese have been described by means of scanning and transmission electron microscopy. Sensillum t₁ is a club-shaped structure, innervated by 3 sensory cells. Each cell is bipolar, with a single dendrite whose ciliary region has a 9-doublet structure. The terminal parts of 2 of the 3 dentrites, filled with many single microtubules, penetrate the cuticular hair, and in the apical swollen region of the sensillum divide into several dendritic branches. The third dendrite terminates as a tubular body at the base of the peg. A sheath-producing cell, a trichogen cell, and one tormogen cell envelop the dendrites. The latter cell has abundant smooth endoplasmic reticulum and produces a very peculiar secretion that is discharged in the space between the cuticular sheath around the dendrites and the cuticle of the hair. A palisade of tubules, 14nm high, is present beneath the cuticle of the apical part of the sensillum; at this level, the cuticle is perforated by numerous pores through which passes a dense material, forming a continuous layer over the cuticle. An olfactory function of sensillum t₁ has been proposed.     

Comparative morphological,anatomical and biochemical studies of the urticating apparatus and urticating hairs of some lepidoptera: Thaumetopoea pityocampa Schiff., Th. processionea L. (Lepidoptera,Thaumetopoeidae) and Hylesia metabus Cramer (Lepidoptera,Saturniidae)

• 1.1. Morphological similarities and differences for the urticating apparatus of three Lepidoptera were studied using a scanning electron microscope.
• 2.2. Complementary anatomical studies of the urticant apparatus were undertaken to explain the morphological results.
• 3.3. Biochemical identity of a thaumetopoein-like protein (an urticating protein) was demonstrated for Thaumatopoea urticating hairs but not for Hylesia moth spicules.
• 4.4. Urticating mechanisms appear to be different across species of Lepidoptera.