Factors that influence the post-emergence growth in Sarcophaga falculata

The post-emergence growth (deposition of endocuticle and growth of skeletal muscles) in Sarcophaga falculata is induced by a blood-borne factor secreted from the head of the pharate adult. The secretion begins 24 to 28 hr before eclosion (at 28°C). A second blood-borne factor, appearing in the haemolymph of the flies a few hours after tanning, suppresses the post-emergence growth in flies, the heads of which have been ligatured at the time of eclosion.     

Ultrastructure of Porocephalus crotali (Pentastomida) cuticle with phylogenetic implications.

The cuticle of P. crotali is pro-arthropodan, composed of an epi-, exo-, and endocuticle. The exo- and endocuticles are separated by a 600-A intermediate cuticular zone. The epicuticle is homogeneous and varies from 100 to 350 A in thickness. The exocuticle varies from 2 to eight mu in thickness and is divided into superficial and deep exocuticular zones. The endocuticle is lamellate and varies from 8 to 30 mu in thickness. Lamellae result from ordered parabolic orientations of 40-A chitin fibrils. Underlying cells lack a basement membrane. Subcuticular muscle cells insert tonofibrils directly into the adjacent endocuticle. No apodemes or apophyses occur.     

Cuticle secretion during larval growth in Drosophila melanogaster

The moulting cycle and growth of the larval integument of Drosophila melanogaster has been studied by light and electron microscopy. Growth during the first, second and third larval instars is accompanied by 3.0-, 3.4- and 3.7-fold increases in surface area, respectively. Growth in surface area occurs continuously during the larval stages, with no detectable relationship to the moulting cycle. Measurements of the thickness of the cuticular layers show that the endocuticle grows in thickness by apposition and in surface area by stretching. The pre-apolytic epicuticle remains at fairly constant thickness during the increase in surface area, indicating that it grows by intussusception of new components. Post-apolytic epicuticle becomes thinner and increases in surface area by stretching. The epicuticle and pre-ecdysial endocuticle are traversed by filaments, but these do not penetrate the endocuticle secreted after ecdysis. We suggest that the filaments transport breakdown products from the old cuticle inward to the epidermis for reutilization. The growth and deposition of cuticle in two larval growth mutants, lethal (2) giant larvae and Chubby Tubby, involves mechanisms similar to those found in wild-type larvae, but in Chubby Tubby the endocuticle contains inclusions which are ultrastructurally similar to dense epicuticle.     

Mode of entry of insecticides in Triatoma infestans

Penetration of insecticides through the integument of adult and nymph V of Triatoma infestans was examined. Intersegmental membranes and the union between dorsal and ventral cuticle appear to be preferential portals of entry of [¹⁴C]parathion in adult insects. In both possible entry points, cuticle has a higher proportion of endocuticle over exocuticle, in comparison to other areas of the integument. In nymph V the whole integument seems to be the entry point for [¹⁴C]parathion, which correlates with its cuticle being almost completely composed of endocuticle. The percent penetration of [¹⁴C]parathion was almost double in nymph V compared with adult insects. The effect of carriers on [¹⁴C]malathion penetration was that they modified the penetration rate and the mode of entry. Differences in the surface distribution of carriers with and without malathion were established.     

Internal and external morphology of the deutonymph of Caloglyphus boharti (Arachnida: Acari)

A band of flexible cuticle encircles the deutonymph, separating the dorsal and ventral plates. The coxae are large, flat and fused with one another to form most of the ventor. Individual coxal margins are redefined as sternites, epimerites or simply apodemes according to which margins fuse with which others. A given area of cuticle may have patches of dark or light cuticle not corresponding to particular structures or cuticular contours; this is a source of confusion to taxonomists. Each leg has a dicondylic coxal-trochantal (adduction-abduction) and trochantal-femoral (promotion-remotion) joint with opposing muscles. The three more distal monocondylic joints (flexion-extension) have only flexor muscles; extension is by increased haemolymph pressure. The five apodemes of the sucker plate provide rigidity; the four suckers attach by a flexible cuticular ring to a solid flange or socket in the sucker plate. The sucker muscles attach to the center of each sucker. The flat, external face of the sucker plate apodemes may complement sucker action by adhesion. Coxal discs and sucker plate discs are identical, contain birefringent cuticular elements, and are considered modified setae. Functional mouthparts and a pharynx are lacking, but a cheliceral anlage is present. The esophagus, midgut and caecae, and malpighian tubules are lumenless and the cells small. The hindgut has a lumen, larger cells and opens externally via the anus. Whereas the digestive tract is regressed, the reproductive system is yet incompletely developed. In older deutonymphs anlagen of ducts, accessory glands and gonads are discernible. The nature of the haemocoel and peritoneum remains nuclear. The central nerve mass is conspicuously large for the size of the deutonymph. The supraesophageal ganglion gives rise to the cheliceral nerves; all other nerves arise from the subesophageal ganglion. Most major nerves were traced to the effector organs. The muscles are divided into leg, dorso-ventral (derived from coxal muscles), dorsal, sucker, and anogenital muscles. The trochantal adductor muscles originate on an endosternite, which is supported by muscles running to the dorsal hysterosoma. The dorso-ventral and propodosomal retractor muscles affect haemolymph pressure. The massive sucker retractor muscles are unique to this instar. Anogenital muscles are not well developed.     

Structure of the cuticle of the common house cricket with reference to the location of lipids

Cuticle segments from the thorax, abdomen, and jumping legs of the house cricket. Acheta domesticus, were examined using histological techniques for light microscopy, scanning and transmission electron microscopy, and direct examination of frozen-fractured cuticle. The surface of untreated cuticle is covered by a lipid film which obscures fine surface detail. Standard EM preparative procedures, as well as washing the cuticle with ethanol before examination, remove this film exposing previously covered openings to dermal gland ducts and wax canals. An epicuticle, exocuticle, mesocuticle, endocuticle, and a deposition layer were present in all transverse sections of cuticle. Light microscopy showed that the exocuticle and mesocuticle are heavily impregnated with lipids, whereas there is little lipid associated with the endocuticle. Frozen-fractured cuticle clearly shows the ‘plywood’ structure of the meso- and endocuticle, while the exocuticle fractures as if it were a solid sheet. The epicuticle is composed of a dense homogeneous layer, cuticulin, outer epicuticle, and the outer membrane. Superficial wax was detected only in cuticle samples prepared using vinylcyclohexane dioxide as a polar dehydrant. The results were used to construct a comprehensive model of the cuticle of A. domesticus.     

The incorporation of precursors into Drosophila larval cuticle

Incorporation of tritiated leucine, tyrosine and glucosamine into the integument of larval Drosophila melanogaster was followed by electron-microscope autoradiography. Tritiated leucine, tyrosine, and glucosamine were incorporated into the endocuticle by apposition, giving rise to a distinct band of label in the endocuticle at a level which depended on the time between labelling and fixation. The labelled amino acids, but not glucosamine, were also detected in the epicuticle and both above and below the distinct labelled band in the endocuticle. The results indicate that the epicuticle grows within the third instar by intussusception of new materials which are transported from the epidermal cells through the endocuticle to the epicuticle. Breakdown of cuticle which was radioactively labelled by feeding larvae tritiated precursors was also followed by autoradiography. The results indicate that the breakdown products from the old cuticle may be reutilized in the synthesis of new cuticle.     

Electron microscopical localization of chitin in the cuticle of Halicryptus spinulosus and Priapulus caudatus (Priapulida) using gold-labelled wheat germ agglutinin: phylogenetic implications for the evolution of the cuticle within the Nemathelminthes

 The ultrastructure of the cuticle of adult and larval Priapulus caudatus and Halicryptus spinulosus is investigated and new features of cuticle formation during moulting are described. For the localization of chitin by TEM wheat germ agglutinin coupled to colloidal gold was used as a marker. Proteinaceous layers of the cuticle are revealed by digestion with pronase. The cuticle of larval and adult specimens of both species consists of three main layers: the outer, very thin, electron-dense epicuticle, the electron-dense exocuticle and the fibrillar, electron-lucent endocuticle. Depending on the body region, the exocuticle comprises two or three sublayers. The endocuticle can be subdivided into two sublayers as well. In strengthened parts such as the teeth, the endocuticle becomes sclerotized and appears electron-dense. Only all endocuticular layers show an intense labelling with wheat germ agglutinin-gold conjugates in all investigated specimens. Additional weak labelling is observed in the exocuticle III layer of the larval lorica of P. caudatus. All other cuticular layers remain unlabelled. Chitinase dissolves the unsclerotized endocuticular layers almost completely, but also exocuticle II and partly the loricate exocuticle III. The epicuticle, the homogeneous exocuticle I and the sclerotized endocuticle are not affected by chitinase. The labelling is completely prevented in all layers after incubation with chitinase. Pronase dissolves all exocuticular layers, but not evenly. The presumably sclerotized regions of exocuticle I are not affected as well as the complete epicuticle and the endocuticle. All cuticular features of the Priapulida are compared with the cuticle of each high-ranked taxon within the Nemathelminthes with special regard to the occurrence of chitin. Based on this out-group comparison it can be concluded that: (1) a two-layered cuticle with a trilaminate epicuticle and a proteinaceous basal layer represents an autapomorphic feature of the Nemathelminthes, (2) the stem species of the Cycloneuralia have already evolved an additional basal chitinous layer, (3) such a three-layered cuticle is maintained as a plesiomophy in the ground pattern of the Scalidophora and (4) in the Nematoida, the chitinous basal layer is replaced by a collagenous one at least in the adults; the synthesis of chitin is restricted to early developmental phases or the pharyngeal cuticle. Accepted: 12 March 1998     

Female ixodid ticks grow endocuticle during the rapid phase of engorgement

Lees (Proc Zool Soc Lond 121:759–772, 1952) concluded that the ixodid tick Ixodes ricinus grows endocuticle during the slow but not during the rapid, phase of engorgement, a conclusion supported by Andersen and Roepstorff (Insect Biochem Mol Biol 35:1181–1188, 2005) for the same species. In this study analysis of dimensional data and cuticle weight measurements from female ixodid ticks (Amblyomma hebraeum) were used to test this hypothesis. Both approaches showed that endocuticle growth continues during the rapid phase, tapering to zero at a fed/unfed weight ratio of ~60. Of the total mass of cuticle in the engorged tick 32–43% was formed during the rapid phase. We demonstrate that if cuticle growth stopped at the end of the slow phase, there would not be sufficient cuticle to account for the thickness of cuticle observed at the end of engorgement. This finding is consistent with prior studies of Rhipicephalus (Boophilus) microplus, and with a dimensional analysis of the cuticle thickness data of Lees for I. ricinus, in contradiction to his conclusion from an analysis of tick cuticle weight measurements. An examination of cuticle weight measurements for I. ricinus by Andersen and Roepstorff similarly supports the finding of cuticle growth during the rapid phase. All ixodid ticks undergo major body expansion, typically tenfold or more, during a rapid phase of engorgement and require sufficient cuticle at the end of that process to contain their body. The fact that cuticle grows during the rapid phase of engorgement in three species suggests that this is a general characteristic of the family Ixodidae.     

Ultrastructure and cuticle formation of the carapace in the myodocopan ostracod exemplified by Euphilomedes japonica (Crustacea: Ostracoda)

The ultrastructure and formation of the cuticle of a myodocopan ostracod, Euphilomedes japonica, are investigated utilizing scanning and transmission electron microscopy. The outer lamella cuticle consists of four layers; epicuticle, exocuticle, endocuticle, and membranous layer like in the cuticle of other arthropods. The exocuticle and endocuticle are well-calcified and the organic matrix develops within the both cuticles. The outermost layer of new cuticle (epicuticle) is secreted first and the inner layers (exocuticle, endocuticle and membranous layer) are added proximally in the pre-, and postmoult stages. The calcification takes place in the whole area of carapace at the same time together with the synthesis of organic matrix within the endocuticle. This study demonstrates that the ultrastructure and formation of the cuticle in myodocopans are different from those in podocopans, and that the myodocopan carapaces have achieved a structural diversity for adaptation to different lifestyles.     

Ultrastructure and formation of the physogastric termite queen cuticle

The physogastric termite queen is the most striking example in insects of growth in size without cuticular moulting. This phenomenon has been studied with electron microscopy and histochemical tests in two species of higher termites, Cubitermes fungifaber and Macrotermes bellicosus. The abdominal hypertrophy (physogastry) is allowed by growth of the arthrodial membranes of the swarming imago. The growth is slow (over several years) but important: the cuticular dry weight is multiplied by 20 in C. fungifaber, by 100-150 in M. bellicosus. The termite queen cuticle arises from the transformation of the cuticle of the swarming imago or imaginal cuticle (unfolding and growing of the epicuticle, stretching of the endocuticle, resorption of the subcuticle) and from the secretion of a new endocuticle or royal endocuticle. The termite queen is the first example known in insects of epicuticular growth. In the physogastric queen, three cuticular types are observed: the rigid cuticle of the sclerites, the soft cuticle of the arthrodial membranes and the partially rigid cuticle of special structures, the neosclerites, which show both rigidity and growth. The fibrillar architecture varies according to the abdominal zones and the position within the cuticle. It appears to be determined by the forces arising from the musculature and the anisometric abdominal growth. The king does not become physogastric, although its cuticle is also modified.     

Integument and sensory nerve differentiation ofDrosophila leg and wing imaginal discs in vitro

Summary An ultrastructural analysis is presented of the cuticular and neural structures formed by the prothoracic leg and wing imaginal discs of maleDrosophila melanogaster larvae during culture in vitro with 0.2 g/ml of -ecdysone. A pupal cuticle, and subsequently an imaginal cuticle with a well-defined epicuticle and a laminated endocuticle is formed. The ultrastructure of the epidermis and of cuticular structures such as bristles, trichomes, apodemes, and tracheoles is very similar to that found in situ. Dendrites and nerve cell bodies are formed in vitro, and sensory axons form nerve bundles similar to those of normal appendages in situ, despite their isolation from the central nervous system. It is concluded that at the ultrastructural level, differentiation in vitro closely parallels the normal course of development.     

Cuticular differences of the exoskeleton relative to habitat preferences among three terrestrial isopods

Terrestrial isopods have adapted to land life by diverse morphological, physiological and behavioral changes. Isopod species exhibit a large variety of preferences ranging from moist to dry habitats. Isopod cuticle is an interesting model for studying adaptations to terrestrial life. The cuticle consists of a hierarchically organized material which provides protection and sites for muscle attachment. The present paper aimed to investigate the structure of the cuticle in three isopod species in order to relate some peculiar features to an adaptive process to environmental constraints. Results showed that general thickness of Ligia italica cuticle was quite similar to that observed in Porcellio lamellatus. Nevertheless, this cuticle was half as thick as in Porcellio laevis. Although the positive relationship found between total body lengths and the total thickness of the cuticle, the exocuticle did not show any differences between the three species. However, it is the development of a thicker endocuticle in P. laevis which make its total cuticle thickness more important.     

Morphology and ultrastructure of the esophagus during the ontogeny of the spider crab Maja brachydactyla (Decapoda,Brachyura, Majidae)

The esophagus of the eucrustaceans is known as a short tube that connects the mouth with the stomach but has generally received little attention by the carcinologists, especially during the larval stages. By this reason, the present study is focused on the morphology and ultrastructure of the esophagus in the brachyuran Maja brachydactyla during the larval development and adult stage. The esophagus shows internally four longitudinal folds. The simple columnar epithelium is covered by a thick cuticle. The epithelial cells of the adults are intensively interdigitated and show abundant apical mitochondria and bundles of filamentous structures. The cuticle surface has microspines and mutually exclusive pores. Three muscle layers surrounded by the connective tissue are reported: circular muscles forming a broad continuous band, longitudinal muscle bundles adjacent to the circular muscles, and dilator muscles crossing the connective tissue vertically toward the epithelium. The connective tissue has rosette glands. The esophagus of the larvae have epithelial cells with big vesicles but poorly developed interdigitations and filamentous structures, the cuticle is formed by a procuticle without differentiated exocuticle and endocuticle, the connective layer is thin and the rosette glands are absent. The observed features can be explained by his role in the swallowing of the food.     

Post‐eclosion temperature effects on insect cuticular hydrocarbon profiles

The insect cuticle is the interface between internal homeostasis and the often harsh external environment. Cuticular hydrocarbons (CHCs) are key constituents of this hard cuticle and are associated with a variety of functions including stress response and communication. CHC production and deposition on the insect cuticle vary among natural populations and are affected by developmental temperature; however, little is known about CHC plasticity in response to the environment experienced following eclosion, during which time the insect cuticle undergoes several crucial changes. We targeted this crucial to important phase and studied post‐eclosion temperature effects on CHC profiles in two natural populations of Drosophila melanogaster. A forty‐eight hour post‐eclosion exposure to three different temperatures (18, 25, and 30°C) significantly affected CHCs in both ancestral African and more recently derived North American populations of D. melanogaster. A clear shift from shorter to longer CHCs chain length was observed with increasing temperature, and the effects of post‐eclosion temperature varied across populations and between sexes. The quantitative differences in CHCs were associated with variation in desiccation tolerance among populations. Surprisingly, we did not detect any significant differences in water loss rate between African and North American populations. Overall, our results demonstrate strong genetic and plasticity effects in CHC profiles in response to environmental temperatures experienced at the adult stage as well as associations with desiccation tolerance, which is crucial in understanding holometabolan responses to stress.     

PORE CANALS AND RELATED STRUCTURES IN INSECT CUTICLE

The fine structure and the distribution of an esterase have been studied in the cuticle of Galleria larvae, Tenebrio larvae and pupae, and in the wax-secreting cuticle of the honey bee, and compared with those in the cuticle of the caterpillar of Calpodes. In Galleria and Tenebrio the pore canals are spaces passing through the lamellate endocuticle from the epithelium to the epicuticle. They contain a filament from the cells which may be concerned in their formation. The shape of the pore canal is probably determined by the orientation of the fibres making up the lamellae in the endocuticle and is not a regular helix. The pore canals also contain numerous filaments of another sort which pass on through the epicuticle and are believed to be the origin of the surface wax. They are particularly abundant in the pore canals of the honey bee wax-secreting cuticle and extend into the cell in long pockets surrounded by an envelope of the plasma membrane. The esterase is probably concerned with the final stage of wax synthesis, for its distribution is similar to that of the lipid filaments.     

Anatomy of the extrinsic gut musculature of Gammarus minus (Crustacea: Amphipoda)

Inserting on the buccal and esophageal foregut of Gammarus minus are numerous pairs of serially arranged dorsal dilator muscles, a single pair of lateral muscles, and two pairs of posterior muscles. Muscles of the cardiac stomach include three dorsal sets, a single pair associated with the pterocardiac ossicles, and two pairs inserting on the ventral aspect. A single pair of muscles inserts on the lateral aspect of the pyloric stomach. The extrinsic muscles of the foregut originate from exoskeletal apodemes of the cephalothoracic cuticle, sockets of the mandible, and a maxillary bridge that lies just ventral to the cardiac stomach. The extrinsic musculature of the hindgut is restricted to the rectal region and consists of paired dorsal and ventral series in an X-configuration. A single unpaired muscle inserts on the ventral midline. Extrinsic muscles of the hindgut originate from the integument of the last pleonic segment. The general arrangement of extrinsic gut muscles in G. minus is similar but not identical to that of other amphipods studied. However, the pattern is quite different from that of other malacostracans.     

Cuticular morphogenesis during continuous growth of the final instar larva of a moth

The larvae of the tobacco hornworm, Manduca sexta, grow continuously. During the feeding period of the fifth larval instar their weight increases ten-fold (ca. 1·2–12 g) accompanied by a four-fold expansion of the surface area of the abdominal cuticle. We have found that this cuticle contains structures which facilitate its expansion. Folds in the epicuticle (papillae) flatten as the cuticle expands. The endocuticle, in contrast, does not unfold but rather is plastically deformed. This plastic deformation is assisted by vertical structures in the cuticle (cuticular columns) which are more easily deformed than the surrounding lamellate cuticle. The head capsule cuticle, which does not expand as the larva grows, lacks papillae and cuticular columns. Thus, these are specialized structures that are reserved for cuticle that must expand as the larva grows.     

Some ultrastructural observations on the integument of a pentastomid

The cuticle of the cephalobaenid pentastomid Reighardia sternae is described at various stages of the moult-intermoult cycle. The intermoult cuticle comprises four layers: an outer epicuticle; an underlying dense layer, the protein epicuticle; a fibrillar endocuticle; and a denser subcuticle. The overall similarity between the structure and composition of these layers and those of insects is discussed. However, the orientation of the chitin-protein fibres in the endocuticle does not show the rotating structure characteristic of many arthropod species, but this does appear in the sclerotized hooks. It is suggested that this comparatively loose, poorly oriented endocuticular structure produces a highly extensible cuticle which is precisely adapted to the specialized, endoparasitic habit of this species. Events at ecdysis, particularly the secretion of moulting fluid and the deposition of cuticulin, follow the insect pattern precisely. The phyletic significance of these observations is discussed.