Structural cuticular proteins in termite queens.

The abdominal cuticle from queens of two termite species, Cubitermes fungifaber and Macrotermes bellicosus, has been investigated with respect to changes occurring during development of physogastry. The following properties have been determined: 1. Relative content of protein and chitin and the percentage of easily extracted protein. 2. Number of proteins separated by electrophoresis and their molecular weights. 3. Amino acid compositions of the intertergal and pleural membranes and of the neosclerites in M. bellicosus. The intertergal and pleural membranes appear to be typical "soft" cuticles, and the neosclerites must also be considered "soft" cuticles, although they are rather rigid.     

Protein synthesis in ‘fat body’ and ovary of the physogastric queen of Macrotermes subhyalinus

In the physogastric queen of Macrotermes subhyalinus the fat body, when incubated in vitro with [¹⁴C] amino acids, synthesizes proteins at a much slower rate than ovarian tissue under the same conditions. Only a very small amount of the labelled proteins is released into the incubation medium. Oxygen consumption of the queen fat body is higher than that of ovarian tissue and the fat body of the king. At 3 hr after injection of [¹⁴C] amino acids in vivo the total fat body of the queen contains three to six times less labelled proteins than the two entire ovaries. It is assumed that in contrast to other insects the physogastric termite queen synthesizes vitellogenins mainly in the ovarian follicle cells and not in the fat body.The fat body of the king with a high incorporation rate of [¹⁴C] amino acids and a rapid release of synthesized protein into the incubation medium is comparable to the fat body of other insects.     

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.     

Ultrastrucuture of the fat body of the reproductive pair in higher termites

The fine structure of the fat body of the higher termite king and queen has been studied both in species with (Macrotermes bellicosus, M. subhyalinus) and without (Cubitermes fungifaber) tracheal rosettes. There is a very pronounced sexual dimorphism. The adipocytes of the queen are highly specialized for protein synthesis and secretion; they store only a small quantity of reserves. The adipocytes of the king are not specialized in protein synthesis, but accumulate large amounts of reserve substances. The previously proposed different functions of the termite queen's fat body are discussed; it appears to be mainly concerned with vitellogenesis.     

Origin and formation of the royal fat body of the higher termite queens

The formation of the royal fat body was studied by electron microscopy in three species of higher termites (Macrotermes bellicosus, Macrotermes subhyalinus, and Cubitermes fungifaber). The swarming alate imago has a storage fat body typical of most insects. In non-physogastric young queens, during the fasting period, the adipocytes deplete their reserves and then, along with the increased vitellogenesis, acquire protein-synthesizing structures (R.E.R.). During the development of physogastry they progressively specialize in protein synthesis and secretion and undergo many cell divisions. The cytological change is paralleled by a spatial reorganization of the fat body. Observations on the transformation of imaginal adipocytes into royal adipocytes show that the royal fat body is derived from the imaginal fat body and not from the tracheal cells as previously claimed.     

The Role of Cuticular Strata Nomenclature in the Systematics of Nemata

A system of cuticular nomenclature based on the strata observed in Enoplia is proposed. Nematode cuticle is divided into four fundamental strata: epicuticle, exocuticle, mesocuticle, and endocuticle. Application of this system allows the correlation of complementary strata throughout Nemata. The major taxonomic categories within Nemata are differentiated on the basis of their cuticular strata as compared with the Enoplia model cuticle.     

Localization of RR-1 and RR-2 cuticular proteins within the cuticle of Anopheles gambiae

The largest arthropod cuticular protein family, CPR, has the Rebers and Riddiford (R&R) Consensus that in an extended form confers chitin-binding properties. Two forms of the Consensus, RR-1 and RR-2, have been recognized and initial data suggested that the RR-1 and RR-2 proteins were present in different regions within the cuticle itself. Thus, RR-2 proteins would contribute to exocuticle that becomes sclerotized, while RR-1s would be found in endocuticle that remains soft. An alternative, and more common, suggestion is that RR-1 proteins are used for soft, flexible cuticles such as intersegmental membranes, while RR-2s are associated with hard cuticle such as sclerites and head capsules. We used TEM immunogold detection to localize the position of several RR-1 and RR-2 proteins in the cuticle of Anopheles gambiae. RR-1s were localized in the procuticle of the soft intersegmental membrane except for one protein found in the endocuticle of hard cuticle. RR-2s were consistently found in hard cuticle and not in flexible cuticle. All RR-2 antibodies localized to the exocuticle and four out of six were also found in the endocuticle. Hence the location of RR-1s and RR-2s depends more on properties of individual proteins than on either hypothesis.     

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.     

Observations on the integument of the water mite Arrenurus major (Acari: Parasitengona)

A study of the integument of the aquatic mite Arrenurus major Marshall is presented. When the cuticle is examined with the unaided eye and the light microscope, it appears to possess numerous tiny pits. However, scanning electron micrographs of the cuticle reveal that it is a solid surface with topographical sculpturing of the epicuticle, indicating that the “pits” are an internal phenomenon. In cuticle which has been sectioned, areas devoid of cuticular material beneath the thin exocuticle are revealed. These areas are the pits which are goblet-shaped. The integument consists of five major strata. These are from the outside to the inside: (1) a superficial layer with a maximum observed thickness of 725 Å, (2) an epicuticle with a thickness of about 900 Å and composed of at least four sublayers, (3) an exocuticle with a thickness of about 1.5 Å. Fibers of the exocuticle are arranged in a Bouligand pattern and exhibit a regularly occurring discontinuity with a spacing of 200 Å. (4) An endocuticle ranging from 15 to 20 μ in thickness. The endocuticle is characterized by bandings which superficially resemble the lamellae of insects but are not homologous, microfibers which exhibit a preferred orientation, and the presence of the pits; and (5) an epidermis lying beneath the endocuticle and extending into the pits. Pore canals are present only in the exocuticle and have their origin at the apices of the pits. The pore canals contain a central filament, and a plug is present just beneath the epicuticle.     

Microscopic anatomy of pycnogonida: I. Cuticle,epidermis, and muscle

The integument of Pycnogonida (Arthropoda) consists of an epicuticle decorated with tubercles and a filamentous coat, an exocuticle with a small number of ill-defined layers, and an endocuticle whose numerous layers are composed of conspicuously cross-banded fibrils. This cuticular periodicity, attributable to cross-linked chitin, has been observed previously in uncalcified and untanned cuticle of many lower crustaceans, especially branchiopods and copepods, and in scattered examples of thin respiratory or excretory cuticles of other arthropods. It is uniformly present in all representatives of all nine pycnogonid families examined to date. Stomodeal, proctodeal, and arthrodial cuticles are devoid of the endocuticular periodicity. The cuticle is decorated with sensory filaments and setae, but is more noteworthy for a dense coverage by glands, up to 1,400/mm². Myocuticular junctions have desmosomal fine structure previously found only in chelicerates. Muscle fine structure is that of slow fibers with long sarcomeres and a high actin to myosin filament ratio, except for cardiac muscle, which has short sarcomeres. Among the arthropods, only merostomates resemble the pycnogonids in the lack of fast somatic muscle fibers. Pycnogonids display a hybrid array of fine structural features that variously serve to relate them to some arthropod subphyla and distance them from others. © 1994 Wiley-Liss, Inc.     

Structure of the integument in Paranthessius anemoniae claus,a copepod associate of the snakelocks anemone Anemonia sulcata (Pennant)

The integument of Paranthessius anemoniae has been studied with light and electron microscopy. A cuticle with clearly defined epicuticular, exocuticular and endocuticular regions overlies a cellular hypodermal layer. The distribution of carbohydrate, lipid and protein components of the cuticle were demonstrated histochemically. Parabolic striations in oblique sections of cuticle suggest that its molecular architecture fits a “twisted sheet” theory proposed for other species. Arthrodial membranes at body and limb joints have a homogeneous structure, lacking exocuticle and endocuticle. Subcuticular glands appear to secrete substances thought to be responsible for the immunity which Paranthessius seems to have to the nematocysts of its host. Small hairs, situated in cuticular cups which occur over the dorsal body surface are considered to function as rheoreceptors.     

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.     

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     

Physical and chemical properties of primary defences in Tenebrio molitor

Prevention and reaction are the foundation for any defence system. In insects, the primary defences against pathogens and parasites limit invasion; the secondary ones (e.g. immune system) act when the cuticle and other primary defences fail. Because investment in both aspects of defence may be costly, they should be regulated in a plastic or variable way in accordance with the risk of infection. The mealworm beetle Tenebrio molitor L. changes cuticle colour and its resistance to fungal infection when subject to high population density, although such resistance is a result of the primary (cuticle) defences rather than the secondary (immunological) ones. The present study tests the hypothesis that the physical and chemical properties of the primary defences in T. molitor change with cuticular darkness. Beetles expressing black phenotypes (or with darker cuticle) have a thicker cuticle, with four well organized layers (epi‐, exo‐, endocuticle and formation zone) and more melanin than tan beetles. The cuticle properties investigated in the present study are likely to be the underlying mechanisms of pathogen resistance in black beetles, including the content of carbonylated proteins, which in black beetles was almost half that of tan beetles after exposure to ultraviolet radiation. It is proposed that, in polyphenic insects (such as mealworm beetles), primary and secondary defences are regulated pleiotropically, with the genes responsible for the expression of one defence having a positive effect on others, whereas, in polymorphic insects, there is no such link and so investment in one defence may impair others.     

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.     

The structure and modification of integumental tissues in Pagurus bernhardus (L.) (Decapoda: Anomura)

The histological structure of cephalothoracic and abdominal integuments has been studied in the hermit crab Pagurus bernhardus (L.). In the branchial region of the carapace, the integument shows a similar structure as described hitherto in a number of other decapod species; there are a thin epicuticle, an exocuticle, and a relatively thick endocuticle, followed by a layer of columnar epithelium and underlying connective tissue. This pattern is repeated on the inner surface of the carapace fold but with generally thinner cuticular layers. Within the connective tissue there are tegumental glands, haemocytes, and some reserve inclusions. The abdominal integument shows a modified cuticle structure which is probably related to its specific function as an adhesive organ attaching the hermit crab to the inner surface of the gastropod shell. The cuticle is uncalcified and it shows deep wrinkles and grooves. Endocuticle and exocuticle are thick and layered whereas the epicuticle is very thin. Large funnel-shaped ducts with secretions occur frequently in the abdominal integument. The cells that are responsible for these secretions are described. The chemical nature of integumental structures has been studied with histochemical tests.     

Postemergence Growth in the Fly <Emphasis Type="Italic">Sarcophaga falculata</Emphasis> initiated by Neurosecretion from the Ocellar Nerve

THE formation of the endocuticle and growth of skeletal muscles which takes place in the fly after eclosion is termed the postemergence growth. An increase in volume of skeletal muscles was observed in Glossina¹ and the deposition of cuticular growth layers described for some orders of both Exopterygota² and Endopterygota³. The postemergence growth which was shown to be induced by some blood-borne factor from the head⁴, hitherto considered to be the tanning hormone bursicon⁵, is initiated by neurosecretion from the ocellar nerve of the pharate adult. Experiments have been performed which indicate that neurosecretion induces the growth of the endocuticle. The process of postemergence growth was assessed by measuring the size of the longitudinal skeletal apodemes. This begins after eclosion and is correlated with the growth in thickness of the cuticle. The enlargement of the surface of the apodemes also indicates the growth of the skeletal muscles, which spread over the newly deposited cuticle. This phenomenon is a constant feature of this species since more than 2,000 specimens were examined at different periods of the year and none were found in which postemergence growth had not occurred.