Calcium translocations during the moulting cycle of the semiterrestrial isopod <Emphasis Type="Italic">Ligia hawaiiensis</Emphasis> (Oniscidea,Crustacea)

Terrestrial isopods moult first the posterior and then the anterior half of the body. During the moulting cycle they retain a significant fraction of cuticular calcium partly by storing it in sternal CaCO₃ deposits. We analysed the calcium content in whole Ligia hawaiiensis and the calcium distribution between the posterior, the anterior ventral, and the anterior dorsal cuticle during four stages of the moulting cycle. The results indicate that: (1) overall, about 80% of the calcium is retained and 20% is lost with the exuviae, (2) in premoult 68% of the calcium in the posterior cuticle is resorbed (23% moved to the anterior ventral cuticle, 17% to the anterior dorsal cuticle, and the remaining 28% to internal tissues), (3) after the posterior moult 83% of the calcium in the anterior cuticle is shifted to the posterior cuticle and possibly to internal storage sites, (4) following the anterior moult up to 54% of the calcium in the posterior cuticle is resorbed and used to mineralise the new anterior cuticle. ⁴⁵Ca-uptake experiments suggest that up to 80% of calcium lost with the anterior exuviae may be regained after its ingestion. Whole body calcium of Ligia hawaiiensis is only 0.7 times that of the fully terrestrial isopods. These terrestrial species can retain only 48% of whole body calcium, suggesting that the amount of calcium that can be retained by shifting it between the anterior and posterior integument is limited. We propose that fully terrestrial Oniscidea rely to a larger degree on other calcium sources like internal stores and uptake from the ingested exuviae.     

The cationic composition and pH in the moulting fluid of Porcellio scaber (Crustacea, Isopoda) during calcium carbonate deposit formation and resorption

Before moulting, terrestrial isopods resorb calcium carbonate (CaCO₃) from the posterior cuticle and store it in sternal deposits. These consist mainly of amorphous calcium carbonate (ACC) spherules that develop within the ecdysial space between the anterior sternal epithelium and the old cuticle. Ions that occur in the moulting fluid, including those required for mineral deposition, are transported from the hemolymph into the ecdysial space by the anterior sternal epithelial cells. The cationic composition of the moulting fluid probably affects mineral deposition and may provide information on the ion-transport activity of the sternal epithelial cells. This study presents the concentrations of inorganic cations within the moulting fluid of the anterior sternites during the late premoult and intramoult stages. The most abundant cation is Na⁺ followed by Mg²⁺, Ca²⁺ and K⁺. The concentrations of these ions do not change significantly between the stages whereas the mean pH changed from 8.2 to 6.9 units between mineral deposition in late premoult, and resorption in intramoult, respectively. Measurements of the transepithelial potential show that there is little driving force for passive movements of calcium across the anterior sternal epithelium. The results suggest a possible role of magnesium ions in ACC formation, and a contribution of pH changes to CaCO₃ precipitation and dissolution.     

Amorphous and crystalline calcium carbonate distribution in the tergite cuticle of moulting Porcellio scaber (Isopoda, Crustacea)

The main mineral components of the isopod cuticle consists of crystalline magnesium calcite and amorphous calcium carbonate. During moulting isopods moult first the posterior and then the anterior half of the body. In terrestrial species calcium carbonate is subject to resorption, storage and recycling in order to retain significant fractions of the mineral during the moulting cycle. We used synchrotron X-ray powder diffraction, elemental analysis and Raman spectroscopy to quantify the ACC/calcite ratio, the mineral phase distribution and the composition within the anterior and posterior tergite cuticle during eight different stages of the moulting cycle of Porcellio scaber. The results show that most of the amorphous calcium carbonate (ACC) is resorbed from the cuticle, whereas calcite remains in the old cuticle and is shed during moulting. During premoult resorption of ACC from the posterior cuticle is accompanied by an increase within the anterior tergites, and mineralization of the new posterior cuticle by resorption of mineral from the anterior cuticle. This suggests that one reason for using ACC in cuticle mineralization is to facilitate resorption and recycling of cuticular calcium carbonate. Furthermore we show that ACC precedes the formation of calcite in distal layers of the tergite cuticle.     

Morphometric analysis of the calcium-transporting sternal epithelial cells of the terrestrial isopods Ligia oceanica, Ligidium hypnorum, and Porcellio scaber during molt

Isopods shed first the posterior and then the anterior half of the body. Before molt, most terrestrial species resorb CaCO3 from the posterior mineralized cuticle. The mineral is stored in anterior sternal deposits, which are used to calcify the new posterior cuticle after molt. For Porcellio scaber it is known that the anterior sternal epithelium has specific structural differentiations for epithelial transport. These differentiations include the plasma membrane surface areas, and the volume fraction of the mitochondria. We analyzed the ultrastructure of the sternal epithelium and used a morphometric approach to study the variations of these parameters between species living in different terrestrial environments. In Ligidium hypnorum, which lives in moist environments, the plasma membrane surface area and volume fraction of mitochondria are much larger than in the semiterrestrial Ligia oceanica. This is in accordance with the relatively larger CaCO3 deposits and shorter time intervals for their formation and resorption in L. hypnorum. For P. scaber, which is adapted to mesic habitats, most values are between those of L. oceanica and L. hypnorum. However, P. scaber has even larger CaCO3 deposits which are formed and degraded within similar time intervals as in L. hypnorum. This unexpected result is considered from the standpoint of more effective mechanisms being present for epithelial ion transport.     

Expression of Ca2+-ATPase and Na+/Ca2+-exchanger is upregulated during epithelial Ca2+ transport in hypodermal cells of the isopod Porcellio scaber

It is thought that a plasma membrane Ca(2+)-transport ATPase (PMCA) and a Na(+)/Ca(2+)-exchange (NCE) mechanism are involved in epithelial Ca(2+) transport (ECT) in a variety of crustacean epithelia. The sternal epithelium of the terrestrial isopod Porcellio scaber was used as a model for the analysis of Ca(2+)-extrusion mechanisms in the hypodermal epithelium. Using RT-PCR, we amplified a cDNA fragment of 1173 bp that encodes a protein sequence possessing 72% identity to the PMCA from Drosophila melanogaster and a cDNA fragment of 791 bp encoding a protein sequence with 50% identity to the NCE from Loligo opalescens. Semiquantitative RT-PCR revealed that the expression of both mRNAs increases from the non-Ca(2+)-transporting condition to the stages of CaCO(3) deposit formation and degradation. During Ca(2+)-transporting stages, the expression of PMCA and NCE was larger in the anterior sternal epithelium (ASE) than in the posterior sternal epithelium (PSE). The results demonstrate for the first time the expression of a PMCA and a NCE in the hypodermal epithelium of a crustacean and indicate a contribution of these transport mechanisms in ECT.     

Membrane particle distribution in the sternal epithelia of the terrestrial isopod Porcellio scaber latr. (Crustacea, oniscidea) during CaCO(3) deposit formation and resorption, a freeze-etch analysis.

The anterior sternal epithelium of terrestrial isopods transports cuticular Ca(2+) to and from large sternal CaCO(3) deposits. We analyzed the anterior and posterior sternal epithelium by the means of the freeze-etch technique and measured the size distribution and density of intramembrane particles (IMPs) during three different molting stages. At least three IMP size classes around 4.5, 7.7, and 9.4 nm can be distinguished on the P-face of the apical and basolateral plasma membrane. An additional size class of around 12.8 nm is restricted to the apical compartment. In the anterior sternal epithelium, the density of these large particles changes by a factor of 1.9 during the molt cycle, suggesting a role in CaCO(3) formation and/or resorption. The density of the smaller IMPs rises transiently by a factor of 1.3 in the posterior sternal epithelium only. The IMP density of the basolateral plasma membrane increases significantly by a factor of 1.4 and 1.3 in the anterior and posterior sternal epithelia, respectively. The results indicate that increases in the IMP density contribute to the differentiation to an increased transport activity during the cyclic enlargements of the plasma membrane surface area in the anterior sternal epithelium.     

Analysis of CaCO3 deposit formation and degradation during the molt cycle of the terrestrial isopod Porcellio scaber (Crustacea,Isopoda)

Terrestrial isopods store cuticular calcium in large sternal deposits composed of an amorphous CaCO(3) compound. A large part of the deposits consists of numerous small spherules that increase the exposed surface to facilitate resorption of CaCO(3) during cuticle mineralization. It is not known how these spherules are formed and how they are dissolved. This paper presents for the first time an analysis of ultrastructural changes occurring in the sternal CaCO(3) deposits of a terrestrial isopod during their formation and degradation. Our results indicate that formation of the spherules takes place in a specialized aggregation zone, in which 10- to 30-nm-thick granules form agglomerations that then increase in size to form spherules that reveal a concentric growth pattern. Degradation of the deposits occurs in a manner that exposes a maximum of surface area on all levels of their structural organization.     

X-ray microprobe analysis of epithelial calcium transport

The sternal epithelium of Porcellio scaber was used as a novel model to study the subcellular elemental distribution in control and Ca(2+)-transporting stages in situ. The anterior sternal epithelium (ASE) is specialized for transport of cuticular Ca to sternal CaCO(3) deposits during premolt, and from these deposits during intramolt. The less specialized posterior sternal epithelium transports Ca(2+) to and from the cuticle. In the ASE cells basal [Na], [Cl], and [Mg] are higher than in the apical side. The basal [Na] increases from 105 to 173 mmol/kg dry mass between control and Ca(2+)-transporting stages, accompanied by a decrease in [Cl] and [K]. The [Mg] increases, suggesting transepithelial Mg(2+)-transport. Cytosolic [Ca] varied insignificantly between 4.5 and 5.7 mmol/kg dry mass, however, the number of Ca hot-spots with concentrations between 15 and 50 mmol/kg dry mass increased during transport. Mitochondrial [Ca] decreased in the ASE from 3.3 in the control to 1.0 in the late premolt and to 2.0 mmol/kg dry mass in the intramolt stage. The results suggest Na(+)-dependent mechanisms for transcellular Ca(2+)-transport and the presence of Ca(2+)-binding proteins. Organelles, probably the smooth endoplasmic reticulum, sequester Ca(2+) during intracellular Ca(2+)-transport. A role of mitochondria as a storage site for cuticular Ca is excluded.     

Molting and cuticle deposition in the subterranean trichoniscid Titanethes albus (Crustacea, Isopoda)

Terrestrial isopods are a suitable group for the study of cuticle synthesis and calcium dynamics because they molt frequently and have evolved means to store calcium during molt. Little data is currently available on molting in Synocheta and subterranean isopods. We studied the molting dynamics in the subterranean trichoniscid Titanethes albus under laboratory conditions and performed a microscopic investigation of sternal CaCO(3) deposits and the tergal epithelium during molt in this species. In accordance with its lower metabolic rate, molting in the laboratory is roughly 2-3 times less frequent in Titanethes albus than would be expected for an epigean isopod under similar conditions. Animals assumed characteristic postures following the molt of each body half and did not consume the posterior exuviae after posterior molt. The structure of sternal calcium deposits and the ultrastructural characteristics of the epidermis during cuticle formation in Titanethes albus are similar to those described in representatives of Ligiidae. During the deposition of the exocuticle, the apical plasma membrane of epidermal cells forms finger-like extensions and numerous invaginations. In the ecdysial space of individuals in late premolt we observed cellular extensions surrounded by bundles of tubules.     

Mineral in skeletal elements of the terrestrial crustacean Porcellio scaber: SRμCT of function related distribution and changes during the moult cycle

Terrestrial isopods moult first the posterior and then the anterior half of the body, allowing for storage and recycling of CaCO₃. We used synchrotron-radiation microtomography to estimate mineral content within skeletal segments in sequential moulting stages of Porcellio scaber. The results suggest that all examined cuticular segments contribute to storage and recycling, however, to varying extents. The mineral within the hepatopancreas after moult suggests an uptake of mineral from the ingested exuviae. The total maximum loss of mineral was 46% for the anterior and 43% for the posterior cuticle. The time course of resorption of mineral and mineralisation of the new cuticle suggests storage and recycling of mineral in the posterior and anterior cuticle. The mineral in the anterior pereiopods decreases by 25% only. P. scaber has long legs and can run fast; therefore, a less mineralised and thus lightweight cuticle in pereiopods likely serves to lower energy consumption during escape behaviour. Differential demineralisation occurs in the head cuticle, in which the cornea of the complex eyes remains completely mineralised. The partes incisivae of the mandibles are mineralised before the old cuticle is demineralised and shed. Probably, this enables the animal to ingest the old exuviae after each half moult.     

Membrane Particle Distribution in the Sternal Epithelia of the Terrestrial Isopod Porcellio scaber Latr. (Crustacea, Oniscidea) during CaCO3 Deposit Formation and Resorption, a Freeze-Etch Analysis

The anterior sternal epithelium of terrestrial isopods transports cuticular Ca²⁺ to and from large sternal CaCO₃ deposits. We analyzed the anterior and posterior sternal epithelium by the means of the freeze-etch technique and measured the size distribution and density of intramembrane particles (IMPs) during three different molting stages. At least three IMP size classes around 4.5, 7.7, and 9.4 nm can be distinguished on the P-face of the apical and basolateral plasma membrane. An additional size class of around 12.8 nm is restricted to the apical compartment. In the anterior sternal epithelium, the density of these large particles changes by a factor of 1.9 during the molt cycle, suggesting a role in CaCO₃ formation and/or resorption. The density of the smaller IMPs rises transiently by a factor of 1.3 in the posterior sternal epithelium only. The IMP density of the basolateral plasma membrane increases significantly by a factor of 1.4 and 1.3 in the anterior and posterior sternal epithelia, respectively. The results indicate that increases in the IMP density contribute to the differentiation to an increased transport activity during the cyclic enlargements of the plasma membrane surface area in the anterior sternal epithelium.     

The Structure and Calcification of the Crustacean Cuticle

The integument of decapod crustaceans consists of an outer epicuticle,an exocuticle, an endocuticle and an inner membranous layerunderlain by the hypodermis. The outer three layers of the cuticleare calcified. The mineral is in the form of calcite crystalsand amorphous calcium carbonate. In the epicuticle, mineralis in the form of spherulitic calcite islands surrounded bythe lipid-protein matrix. In the exo- and endocuticles the calcitecrystal aggregates are interspersed with chitin-protein fiberswhich are organized in lamellae. In some species, the organizationof the mineral mirrors that of the organic fibers, but suchis not the case in certain cuticular regions in the xanthidcrabs. Thus, control of crystal organization is a complex phenomenonunrelated to the gross morphology of the matrix. Since the cuticle is periodically molted to allow for growth,this necessitates a bidirectional movement of calcium into thecuticle during postmolt and out during premolt resorption ofthe cuticle. In two species of crabs studied to date, thesemovements are accomplished by active transport effected by aCa-ATPase and Na/Ca exchange mechanism. The epi- and exocuticular layers of the new cuticle are elaboratedduring premolt but do not calcify until the old cuticle is shed.This phenomenon also occurs in vitro in cuticle devoid of livingtissue and implies an alteration of the nucleating sites ofthe cuticle in the course of the molt.     

In vivo and in vitro effects of the nonsteroidal ecdysteroid agonist tebufenozide on cuticle formation in Spodoptera exigua: An ultrastructural approach

To evaluate the ecdysteroid-like mode of action of tebufenozide (RH-5992), the effects on the fine structure of the integument in last- and third-instar larvae of the beet armyworm, Spodoptera exigua, and on cuticle formation in cultured imaginal wing discs, were studied. After 3 h of treatment with tebufenozide, the first signs of a normal moult were observed in treated larvae. A few hours later, ecdysial space formation and secretion of a new epicuticle were started. Furthermore, the new cuticle was incomplete in treated larvae; the new procuticle was absent or contained only a very low number of lamellae. In addition, epidermal cells showed many vacuoles and symptoms of degeneration with increase in time. Only a few lamellae of the old procuticle were digested, and normal ecdysis was inhibited which led to the presence of a double cuticle within 24–48 h after treatment. Similarly, cultured discs were stimulated to deposit a new cuticle within 12 h after cultivation in a medium containing tebufenozide. Our observations in treated S. exigua larvae on the one hand and in imaginal discs cultured with tebufenozide on the other hand are indicative of a hyperecdysteroid action, and confirm that the moult accelerating mode of action of tebufenozide resulted in a forced, untimely synthesis of cuticle by activation of epidermal or epithelial cells, and that its ecdysis inhibitory activity is mediated by its effect on post-apolysis processes. © 1996 Wiley-Liss, Inc.     

Moult cycle and morphogenesis inHyas araneus larvae (decapoda,majidae), reared in the laboratory

Moult cycle and morphogenesis in larval instars (zoea I, zoea II, megalopa) of the spider crabHyas araneus (L.) were studied in the laboratory. Changes in the epidermis and cuticle were documented photographically at daily intervals to characterize the stages of the moult cycle. Stage A (early postmoult) is a very short period during which the larva takes up water. During late postmoult (B) and intermoult (C) the endocuticle is secreted, and there is conspicuous epidermal tissue condensation and growth. The onset of early premoult (D₀) is characterized by epidermal apolysis, occurring first at the bases of the setae in the telson of zoeal instars or in the rostrum of the megalopa, respectively. Intermediate premoult (D₁) is the main period of morphogenesis, in particular of setogenesis: in the setae of the zoeal telson and carapace there is invagination or (in the zoea II) degeneration of epidermal tissues. Formation of new setae in the interior of epidermal tubules was observed in zoeal maxillipeds and in the antennae of the zoea II and megalopa instars. During late premoult (Stages D_2–4) part of the new cuticle is secreted, and the results of morphogenesis become clearly visible. For technical reasons (rigid exoskeleton) only a preliminary account of the moult cycle in the megalopa can be given. A time schedule is suggested for the stages of the moult cycle. It is estimated that postmoult (A–B) takes ca 9 to 15 % of total instar duration, intermoult (C) ca 22 to 37 %, and premoult (D) ca 48 to 69 %. There is an increasing trend of relative portions of time (% of total instar duration) from instar to instar in Stages A–C (mainly in the latter) and a decreasing trend in Stage D (mainly in D₀ and D_2–4).     

The formation of the epicuticle and associated structures inOniscus asellus (Crustacea,Isopoda)

Summary The integument of the woodlouse,Oniscus asellus, consists of a two-layered epicuticle, a largely lamellate procuticle — itself divided into two regions (pre-and postecdysial cuticles), and the epidermis. At the initiation of new cuticle production the epidermal cells become vacuolated and retract away from the cuticle. Apolysis occurs immediately after the cessation of postecdysial cuticle production. The formation of the epicuticle is unique among the arthropods since material aggregates along the distal epidermal membrane. By indenting, doubling back on itself, and incorporating septa, the epicuticle forms surface structures such as plaques and tricorns.The innervation, and so the receptive function of the tricorns is confirmed, but since there is no connection between the old and new receptors during premoult, sensory information from these exoreceptors must be severely curtailed. This may explain the biphasic moult in all isopods since it ensures that only half the body experiences this sensory deprivation at any one time. In terrestrial species there is the additional advantage of restricting the area of permeable new cuticle. The frequency of moulting may be due to the need to renew disrupted receptor surfaces.Tricorns do not appear to be the mechanoreceptors involved in the marked thigmotactic response of woodlice since they do not have the typical internal structure of such receptors; rather, the dendrite —which extends into the lumen of the tricorn —is protected from deformation by the previously unreported combination of a dendritic sheath and a cuticular tube. The modality of tricorns is possibly one of hygro-perception. One of the behavioural responses of woodlice to desiccation is aggregation. The numerical distribution of tricorns over the body surface is admirably suited to assist in the formation and maintenance of such aggregates during desiccation and to their observed dispersal when the relative humidity rises.     

Ultrastructure of the integument during moulting of the quiescent tritonymphal instar of trombiculid mite Hirsutiella zachvatkini (Acariformes: Trombiculidae)

The ultrastructure of the integument of the quiescent reduced tritonymph of the trombiculid mite Hirsutiella zachvatkini (Schluger) was investigated by means of transmission electron microscopy. Mites were investigated daily during the 14–16 day tritonymphal period (imagochrysalis). This period includes the deutonymphal moult (1–3 days), the quiescent tritonymph period (2–4 days), and the tritonymphal moult into the adult mite (6–10 days). A distinct recognizable feature of the tritonymphal moulting cycle is a sequence of events independent of precise time intervals. This process involves partial destruction and reorganization of the hypodermis of the previous instar, and formation of a new hypodermis of the subsequent instar from islands of rudimentary hypodermal cells. The integument of the reduced tritonymph differs greatly from that of both larva and active deutonymph and adult. It consists of a simply organized hypodermal layer of varying thickness and a thick clear poorly lamellate cuticle with curved pore canals, and lacking setae. The epicuticle is very thin and without a clear protein layer. The tritonymphal instar as such with its own cuticle situated near the hypodermis is encased within the detached covering of the previous active deutonymph, and may be considered a calyptostasic and entirely pharate instar. There is a tendency for reduced tritonymphal stage to be eliminated from ontogenesis and this stage is not homologous to the pupa of insects.     

Tissue accumulation and the moult cycle in juveniles of the Australian freshwater crayfish Cherax destructor

1. This paper investigates moult stage and size-specific changes in whole body composition during growth in juvenile crayfish in order to better describe the nature of growth and energy use. 2. Composition is described in terms of moult stage and size-specific wet, dry and ash-free dry weight, water, carbon, protein nitrogen, non-protein nitrogen, ash and energy. Dry weight and ash-free dry weight (AFDW) peaked in the middle and in the later stages of premoult. Both peaks were about 2–2.3 times postmoult weight. Losses in tissue weight during ecdysis were substantial in the smallest crayfish but declined with size. Water was taken up between late premoult and early postmoult. Tissue accumulation occurred primarily between B and D₁.₃, with further weight gain largely the result of fluid uptake. Ash increased immediately postmoult with a major peak occurring during intermoult. Mean organic carbon varied between 33 and 35.5% of the body and 49% of the exuvia. Chitin varied between 9 and 17% of body AFDW and made up about 50.5% of the exuvia. Protein content varied between 47 and 62% of body AFDW and about 25% of the exuvia. Carbon, chitin and protein were not affected by moult stage but protein declined with ocular carapace length (OCL) in larger crayfish. Mean caloric content varied between 19 and 22 J mg-¹ AFDW depending on size and moult stage. Caloric content increased with OCL during premoult and early intermoult then declined with size until part of the way through premoult. 3. Relationships between protein, chitin and remaining carbon (organic carbon minus chitin) were examined. It is suggested that protein and some carbon are catabolized during the moulting process, possibly to fuel metabolism. Models are presented showing changes in proximate composition over the moult cycle for two sizes of crayfish, and tissue and energy accumulation and loss over a series of moult cycles and sizes from 3.1 mm to 17 mm OCL.     

Fluoride in tissues of Krill Euphausia superba Dana and Meganyctiphanes norvegica M. Sars in relation to the moult cycle

Summary The fluoride content of whole animals and different tissues of the euphausiid species Euphausia superba and Meganyctiphanes norvegica was analyzed by two different and improved methods of isolation and determination. In contrast to other authors our findings show that the internal organs (muscle, hepatopancreas and hemolymph) contain less than 6 ppm d.w. fluoride this being the same order of magnitude as for vertebrates. The high concentrations reported by other authors must be mainly due to contamination of the soft tissue during storage (post-mortem migration of fluoride from shell) and/or contamination caused by minute fractions of cuticle during dissection. Over 99% of the total fluoride content is located in the cuticle (i.e. integument) of the euphausiids (2600 ppm/d.w. in E. superba and 3300 ppm/d.w. in M. norvegica in pleon cuticle). Analysis of F^- levels in relation to the moulting cycle showed that the uptake in both euphausiids occurs at a comparable and fast rate during the same physiological phase shortly after moult, parallel to the general construction of the cuticle. The internal organs show homeostasis in respect to fluoride. Accordingly, no internal deposition takes place, and F^- is reaccumulated from the external medium at each moult.This work was supported by grants from the DFG No. Ad 24/9 and Bu 548/1     

Calcium,phosphorus and adenylate levels and Na(+)-K(+)-ATPase activities of prawn,Macrobrachium nipponense,during the moult cycle

Changes in calcium and phosphorus concentrations, adenylate (AMP, ADP and ATP) levels, and ratios and ATPase activities of Macrobrachium nipponense were investigated during the moult cycle. Ca level in the exoskeleton was lowest in early postmoult (stage A), increasing at stages B and through intermoult (stage C) and peaking in premoult (stage D1 and D2). The P concentrations in the exoskeleton and muscle in late premoult and early postmoult stages were higher than those at other moult stages, and were lowest in the intermoult. Muscle adenylate energy charge (AEC) changed with moult stages, and was in agreement with the change in inorganic P level in the muscle. AEC may be a direct indicator of energy metabolic activity during the moult cycle. ATP/ADP and ATP/AMP ratios in premoult and postmoult stages were higher than that in intermoult stage. Na(+)-K(+)-ATPase activities of gills, muscles and hepatopancreatic of prawns were higher in early postmoult and late premoult animals, whereas they were lower in late postmoult, intermoult and early premoult animals. Gill residual ATPase activity was significantly higher in postmoult animals, while the peak value of hepatopancreatic residual ATPase activity appeared in intermoult stage.     

Ultrastructural Effects of a Non-Steroidal Ecdysone Agonist,RH-5992, on the Sixth Instar Larva of the Spruce Budworm,Choristoneura fumiferana

Force feeding of RH-5992 (Tebufenozide), a non-steroidal ecdysone agonist to newly moulted sixth instar larvae of the spruce budworm, Choristoneura fumiferana, (Lepidoptera: Tortricidae) initiates a precocious, incomplete moult. Within 6h post treatment (pt) the larva stops feeding and remains quiescent. Around 12hpt, the head capsule slips partially revealing an untanned new head capsule that appears wrinkled and poorly formed. By 24hrpt, the head capsule slippage is pronounced and there is a mid-dorsal split of the old cuticle in the thoracic region but there is no ecdysis. The larva remains moribund in this state and ultimately dies of starvation and desiccation. The temporal sequence of the external and internal changes of the integument were studied using both scanning and transmission electron microscopy. Within 3hpt, there is hypertrophy of the Golgi complex indicating synthetic activity and soon after, large, putative ecdysial droplets are seen. Within 24h, a new cuticle that lacks the endocuticular lamellae is formed. The formation of the various cuticular components, the degradation of the old cuticle and changes in the organelles of the epidermal cells of the mesothoracic tergite are described. The difference between the natural moult and the one induced by RH-5992 are explained on the basis of molecular events that take place during the moulting cycle. The persistence of this ecdysone agonist in the tissues permits the expression of all the genes that are up-regulated by the presence of the natural hormone but those that are turned on in the absence of the hormone are not expressed.