Phenoloxidases from larval cuticle of the sheep blowfly,Lucilia cuprina: Characterization,developmental changes,and inhibition by antiphenoloxidase antibodies

A tyrosinase, enzyme A (EC 1.10.3.1, o-diphenol: O₂ oxidoreductase), and a laccase, enzyme B (EC 1.10.3.2, p-diphenol: O₂ oxidoreductase), have been partially purified and characterized from larval cuticle of the sheep blowfly, Lucilia cuprina. Enzyme A is active toward a range of o-diphenols but not p-diphenols, is strongly inhibited by thiourea and phenylthiourea, has a pH optimum between 6.5 and 7.0, and yields a single, 60,000 molecular weight subunit following SDS gel electrophoresis. Enzyme B is active toward both o-diphenols and p-diphenols, is only slightly inhibited by phenylthiourea, has a pH optimum near 4.5, is highly thermostable, and has an apparent molecular weight of 90,000. Enzyme A appears to be activated from an inactive proenzyme in the cuticle and to be present throughout the wandering phase of the final larval instar, declining at pupariation. Enzyme B is present in active form, increases greatly in the cuticle just at the time of pupariation, and then decreases as sclerotization occurs. Antibodies against enzyme A have been raised in sheep and rabbits, and against enzyme B in rabbits, but diets containing antiphenoloxidase antibodies did not affect development or mortality of fly larvae.     

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.     

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.     

An enzyme from Myrothecium verrucaria that degrades insect cuticles for biocontrol of Aedes aegypti mosquito

Summary Myrothecium verrucaria produced a high activity of extracellular insect cuticle degrading enzymes, chitinases, proteinases and lipases. Both first (I) instar and fourth (IV) instar larvae of a mosquito, Aedes aegypti, a vector of yellow fever and dengue, were susceptible to crude culture filtrate (100% mortality within 48 h at 170 mg/l) . The supplementation of purified M. verrucaria endo-chitinase with commercial lipase decreased the lethal time (LT₅₀) from 48 h to 24 h for I instar and 120 h to 96 h for IV instar. Our results of the larvicidal activity indicate that the cuticle degrading enzyme complex of M. verrucaria has a good potential for the control of mosquitoes.     

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.     

Cyanoglucoside storing cuticle of Zygaena Larvae (Insecta,Lepidoptera)

Summary As a deterrent against predators, larvae of Zygaena trifolii release droplets of fluid containing cyanoglucosides from segmentally arranged cuticular cavities. Histological examinations show that during the moulting period, the old cuticle, including the cavities and the secretion within them, is degraded, with the exception of a thin mesocuticular layer forming the exuviae. When the endocuticular layer of the new cuticle is deposited, the cuticle detaches from the underlying epidermis in specific areas, which leads to the formation of the cuticular cavities. During a moult-intermoult sequence the concentration of cyanoglucosides in both the haemolymph and the defensive secretion shows specific changes. These changes seem to be related to the formation and degradation of the cavities. We suggest that during the moult the cyanoglucosides are transported through the epidermis into the haemolymph to prevent them from being wasted with the exuviae and, after ecdysis, are retranslocated into the newly formed cavities.     

Biometric studies of some stoneflies and a mayfly (Plecoptera and Ephemeroptera)

Aspects of the nymphal/adult developmental change were investigated in biometric studies of several species of Plecoptera: Nemouridae near Schlitz, Hesse, Germany. Preliminary information on the mayfly, Baetis vernus Curtis, is also provided. Nemourid nymphs pass through 3 wing bearing stages before reaching adulthood. Instars can be identified by their characteristic shapes, as expressed by the wing length/head width (WL/HW) ratio. Size does not allow instar discrimination, mainly due to sexual size differences. HW is ca 10% larger in last instar female than in male nemourid nymphs; exuviae shed at the moult to adult represent about 14% of nymphal ash free dry weight (AFDW). Biomass lost with exuviae during the many larval moults should be accounted for in estimates of production. Freshly emerged nemourid females are about 6% larger and 30% heavier than males. The HW/AFDW relationship is the same in both sexes. Through terrestrial feeding during adult life, males double their weight on average. Mature females are up to three times heavier than freshly emerged ones. They invest about 30% of their final AFDW in reproduction.Shape of last instar nymphal Baetis was expressed as the ratio wing length/mesonotum length. It is size-dependent, a characteristic, instar-specific shape may not occur in this mayfly. Nymphal and subimaginal exuviae together represent about 14% of last instar nymphal dry weight. Females of Baetis are about 55% heavier than males. Unlike in Plecoptera, the size/weight (ML/AFDW) relationship differs between sexes.     

The characteristics of encapsulated whole cell β-galactosidase

We prepared encapsulated whole cell β-galactosidase using E. coli. The cell culture was divided into two steps for the cell accumulation inside the capsule and enzyme production in the cell. Growth and production media were used individually for this purpose. The dry cell weight of the free cell culture was increased 2.8 times by controlling the pH of the growth medium during cultivation. However, the weight of cells accumulated in the capsule reduced 40% with pH control. The dry cell weight increased with lactose concentration of the production medium for both cases of free and capsule cultures. The dry cell weights were 1.5?g/l for free culture and 100?g/l in the capsule when the lactose concentration of the production medium was 10?g/l. The dry cell weight increased about 60% for both cases as the lactose concentration increased from 10 to 50?g/l. The specific activity of whole cell enzyme decreased with lactose concentration from 5 to 1.4?unit/g dry cell for free culture and from 1.1 to 0.65?unit/g dry cell in the capsule. The value of Michaelis constant, K_m, of whole cell enzyme increased 3 times because of the resistance of mass transfer through the capsule membrane. The constants of Michaelis-Menten equation for the whole cell enzyme in the capsule were V_m: 0.0479?mM/min and K_m: 44.86?mM. These constants of the membrane-free cells were V_m: 0.0464?mM/min and K_m: 15.64?mM. To increase the whole cell enzyme activity, we treated encapsulated cells with organic solvents. The activity of encapsulated whole cell enzyme was increased 3.5 times with the treatment of chloroform and ethanol. The activity of the encapsulated whole cell enzymes was reserved after repeating the process 30 times.     

Juvenile hormone esterase is a biochemical anti-juvenile hormone agent

Juvenile hormone esterase, purified by affinity chromatography from the larval hemolymph of Manduca sexta in the fifth stadium, was injected into larvae of the same species in the earlier stadia resulting in a blackening of the cuticle following ecdysis to the next larval stadium. This anti-juvenile hormone response was dose-dependent for an injection in the second, third or fourth stadium. Cuticular blackening was prevented by treating larvae with the juvenoid epofenonane. Larval response to injected juvenile hormone esterase also varied with the time of injection within a single stadium, having a maximum effect for injections at the time of head capsule slippage. Juvenile hormone esterase activity measured from the hemolymph after injection of larvae in the second stadium decreased over an 11 h time-course. Because the anti-juvenile hormone effects resulting from a single injection of juvenile hormone esterase were dependent on the time of injection, it appears that when juvenile hormone biosynthesis is active in the insect, the duration of enzyme activity limits the anti-juvenile effects that can be induced.     

Prophenoloxidase activation in the hemolymph of Sarcophaga bullata larvae

Phenoloxidase in the hemolymph of Sarcophaga bullata larvae is present as an inactive proenzyme form. Localization studies indicate that the majority of the prophenoloxidase is present in the plasma fraction whereas only a minor fraction (about 4%) is present in the cellular compartments (hemocytes). Inactive prophenoloxidase can be activated by zymosan, not by either endotoxin or laminarin. This activation process is inhibited by the serine protease inhibitors, benzamidine and p-nitrophenyl-p～-guanidobenzoate. Exogenously added proteases, such as chymotrypsin and subtilisin, also activated the prophenoloxidase in the whole hemolymph but failed to activate the partially purified proenzyme. However, an activating enzyme isolated from the larval cuticle, which exhibits trypsinlike specificity, activated the partially purified prophenoloxidase. Inhibition studies and activity measurements also revealed the presence of a similar activating enzyme in the hemolymph. Thus, the phenoloxidase system in Sarcophaga bullata larval hemolymph seems to be comprised of a cascade of reactions. An endogenous protease inhibitor isolated from the larvae inhibited chymotrypsin-mediated prophenoloxidase activation but failed to inhibit the cuticular activating enzyme-catalyzed activation. Based on these studies, the roles of prophenoloxidase, endogenous activating proteases, and protease inhibitor in insect immunity are discussed.     

Control of ommochrome synthesis by both juvenile hormone and melanization hormone in the cabbage armyworm,Mamestra brassicae

Summary Pigmentation of last instar larvae of the cabbage armyworm,Mamestra brassicae is of two types: melanin in the cuticle and ommochrome in the epidermis. The latter was found to be primarily xanthommatin. When allatectomy was performed 8 h before head capsule slippage (HCS) in the last larval molt, later ommochrome synthesis was inhibited. Application of juvenile hormone (JH) up to 12 h after HCS (9 h before ecdysis) (activity: methopreneJH I>JH II>JH III) restored ommochrome synthesis. After that time it has less and less effect.Removal of the suboesophageal ganglion from the larvae 8 h before HCS prevented both later ommochrome synthesis and melanization. Melanization of isolated abdomens was restored by implantation of 3 suboesophageal ganglia or injection of melanization and reddish coloration hormone (MRCH) 18 h after HCS. Restoration of ommochrome synthesis required exogenous JH in addition to melanization hormone from suboesophageal ganglion or MRCH. Therefore, melanization appears to be critical for the later onset of ommochrome synthesis even in a larva which has been exposed to JH during the critical period.Abbreviations CC·CA corpora cardiaca-corpora allata complex - JH juvenile hormone - MRCH melanization and reddish coloration hormone - HCS head capsule slippage     

PARASITÄRE VERÄNDERUNGEN DER WIRTSKUTIKULA BEI PIERIS BRASSICAE UND CYDIA POMONELLA DURCH ENTOMOPHAGE ENDOPARASITEN

Zusammenfassung An den Wirt-Parasit-Systemen Pieris brassicae-Apanteles glomeratus sowie Cydia pomonella-Ascogaster quadridentatus wurde der parasitäre Einfluß auf die Kutikula der Wirtsraupen im 5. Stadium histologisch und chemisch untersucht. Die Dickenentwicklung der Exo-und insbesondere der Endokutikula unterliegt einer starken parasitären Hemmung, die bei beiden Wirt-Parasit-Systemen schließlich in einer Reduktion der Dicke und des Trockengewichts um etwa 50% bis 58% resultiert. Der Parasitismus von Apanteles wirkt sich schon in der frühen Aufbauphase der Kutikula auf deren Wachstum und Eigenschaften aus und verändert auch im weiteren Verlauf die Kutikulaentwicklung. Qualitative Veränderungen betreffen die Dichte und chemische Zusammensetzung. Besondere Gewichtsdefizite beim Stickstoff sowie bei der alkalilöslichen Fraktion zeigen an, daß insbesondere der Einbau von Proteinen, aber auch die chemische Stabilisierung des Chitin-Protein-Komplexes gehemmt sind.

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Summary Parasitism by Apanteles glomeratus and Ascogaster quadridentatus affects the development of cuticle of the host larvae, Pieris brassicae and Cydia pomonella, respectively. Inhibitory parasitic effects on cuticular growth of the host during its last larval instar are evident in differences in surface area, thickness and dry weight of the integument. They amount to 32% reduction in surface area, 56% of thickness and 54% of dry weight in Pieris and to 37%, 50% and 58% in Cydia. Thickness of endocuticle is reduced much more than that of exocuticle. This may be due to the continuous influence of the parasite larvae on the deposition of endocuticular material during the intermoult period.Extraction of cuticles with hot water and hot 5% aqueous potassium hydroxide revealed changing differences between the relative amounts of the three fractions, obtained by this treatment. Relative gain of dry weight is less in the alkali-soluble fraction of parasitized Pieris and Cydia. Deficiency of nitrogen (29% to 62% in water extract and 56% to 75% in alkali extract) is generally greater than reduction of total cuticle dry weight. This is more pronounced in the alkali-soluble fraction than in the water extract.These data suggest that the presence of parasites has greatest effect on incorporation of nitrogenous compounds. Moreover, chemical stabilization of the chitin-protein complex seems to stop earlier and to be less perfect in parasitized caterpillars. Since specific gravity of dry cuticle is also subject to effects of parasites, it is assumed that in the investigated hostparasite associations the cuticle of parasitized hosts differs from unparasitized ones in quantity, physical quality and chemical composition.

     

Role of an extracellular neutral protease in infection against nematodes by <Emphasis Type="Italic">Brevibacillus laterosporus</Emphasis> strain G4

Proteases have been proposed as virulence factors in microbial pathogenicity against nematodes. However, what kinds of extracellular proteases from these pathogens and how they contribute to the pathogenesis of infections against nematode in vivo remain largely unknown. A previous analysis using a strain with a deletion in an extracellular alkaline protease BLG4 gene from Brevibacillus laterosporus demonstrated that BLG4 was responsible for the majority of nematicidal activity by destroying host’s cuticle. In recent studies, a neutral protease NPE-4, purified from the mutant BLG4–6, was found to be responsible for the majority of the remaining EDTA-inhibited protease activity. However, the purified NPE-4 and recombinant NPE-4 in a related species Bacillus subtilis showed little nematicidal activity in vitro and were unable to degrade the intact cuticle of the host. It is interesting to note that the addition of NPE-4 improved the pathogenicity of crude enzyme extract from wild-type B. laterosporus but had no effect on the BLG4-deficient mutant. This result suggests that NPE-4 functions in the presence of protease BLG4. Moreover, NPE-4 could degrade proteins from the inner layer of purified cuticles from nematode Panagrellus redivivus in vitro. These results indicated that the two different bacterial extracellular proteases might play differential roles at different stages of infection or a synthetic role in penetration of nematode cuticle in B. laterosporus. This is among the first reports to systematically evaluate and define the roles of different bacterial extracellular proteases in infection against nematodes.     

Effects of the ecdysteroid agonists RH 5849 an RH 5992, alone and in combination with a juvenile hormone analogue, pyriproxyfen, on larvae ofSpodoptera exigua

Biological activity assays with RH 5849 and RH 5992 indicated that both compounds affected growth and development of last-instar larvae ofSpodoptera exigua (Hübner) (Lepidoptera: Noctuidae) in a dose-dependent manner. Within the first 24 h after treatment by continuously offering leaves dipped in a water solution of ≥50 mg/l RH 5849 and ≥0.5 mg/l RH 5992, symptoms of a prematurely induced larval moult and head capsule apolysis were visible. Intoxicated larvae died shortly afterwards, showing signs of unsuccessful ecdysis. LC₅₀-values of RH 5849 and RH 5992 for fifth-instarS. exigua larvae were 110 and 2.5 mg/l, respectively. Pyriproxyfen alone affected the larval stage and disturbed normal metamorphosis. One supernumerary larval instar occurred occasionally. LC₅₀-value for pyriproxyfen was 1.7 mg/l. Larvae simultaneously treated with RH 5849 or RH 5992 and pyriproxyfen, continued to grow until they attained a size and weight about 2–3 times that of the controls. This growth was accompanied by at least one and sometimes two supernumerary moults. Concerning thein vivo imaginal wing disc growth and development, only in larvae treated with 10 and 50 mg/l RH 5849 or 0.5 mg/l RH 5992, tracheole migration was observed earlier than in the controls. When applying 300 mg/l RH 5849 or 3–7 mg/l RH 5992, the discs remained small and no signs of tracheole migration were observed. In larvae simultaneously treated with RH 5849 or RH 5992 and pyriproxyfen, tracheole migration was not prematurely induced and a pupal cuticle was produced in the discs of larvae, undergoing a supernumerary moult. No clear signs of evagination were observed.     

Morphology and development of <Emphasis Type="Italic">Pteromalus cerealellae</Emphasis> (Ashmead) (Hymenoptera: Pteromalidae) on <Emphasis Type="Italic">Callosobruchus maculatus</Emphasis> (F.) (Coleoptera: Chrysomelidae)

Pteromalus cerealellae (Ashmead) (Hymenoptera: Pteromalidae) is an ectoparasitoid of several stored-product insect pests. Very little information has been published on its biology and development in host larvae, which typically are concealed within seeds. We documented the development of P. cerealellae within fourth instar larvae of its concealed host, Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae) infesting cowpea seeds. The preimaginal life stages of the parasitoid were characterized for the first time using morphological structures revealed by microscopic techniques including scanning electron microscopy. Pteromalus cerealellae produces hymenopteriform eggs and larvae. Eggs hatch into 13-segmented first instar larvae with peripneustic condition of spiracles. The larvae have simple, tusk-like mandibles, whereas the mandibles of the pupae and the adults are of the conventional toothed types. Using statistical analyses of the sizes of the larval mandibles and head capsules in conjunction with reliable characters such as the number of exuviae on the body of parasitoid larvae, cuticular folding, and excretion of the meconium, we recorded four larval instars for P. cerealellae. The data showed significant positive correlations between larval mandible lengths and widths of larval head capsules, as well as between mandible lengths and larval instars, suggesting that mandible length is a good predictor of the number of instars in P. cerealellae. Developmental time from egg to adult emergence was ∼12 d for females and ∼11 days for males at 30 ± 1°C, 70 ± 5% r.h. and 12L:12D photoperiod.     

Impact of Embryonopsis halticella eaton larvae (Lepidoptera: Yponomeutidae) feeding in Marion Island tussock grassland

Summary Embryonopsis halticella is a brachypterous moth endemic to the Kerguelen Province of sub-Antarctic islands. Its larvae are strictly host-specific grass-borers of the tussock grass Poa cookii, and are the major herbivores on Marion Island. Monthly sampling over one year (1984) on Marion Island showed that E. halticella larvae reach a biomass of 0.222 g m^-2 (dry mass) in P. cookii grassland in summer. In feeding experiments conducted in the laboratory on Marion Island, larvae consumed 0.3 X their own live mass in leaf material daily. Extrapolated consumption rates in the field range from 1 kg ha^-1 month^-1 in winter to 18 kg ha^-1 month^-1 (dry mass) in summer. Total annual consumption, based on leaf feeding only, amounts to 86 kg ha^-1 (dry mass). Significant shifts in diet from foliage to seeds occur during spring, and larvae also consume their own frass and exuviae. It is calculated that E. halticella larvae remove 2.5% of the annual production of Poa cookii in Marion Island tussock grassland.     

Roles of dopa decarboxylase and phenoloxidase in the melanization of the tobacco hornworm and their control by 20-hydroxyecdysone

Summary WhenManduca sexta larvae are allatectomized 5 h before head capsule slippage (HCS) in the final larval molt, the new larval cuticle contains granules that melanize 3 h before ecdysis when the ecdysteroid titer falls (Curtis et al. 1984). In both the epidermis and hemolymph of these allatectomized larvae dopamine was higher than dopa prior to and at the time of melanization. Dopamine also increased in the new cuticle as melanization began. Dopa decarboxylase (DDC) activity increased in the epidermis, cuticle, and fat body beginning 16 h after HCS, with a two-fold greater increase in the epidermis of allatectomized larvae. Both -MDH and -fluoromethyl-dopa inhibited epidermal DDC activity and inhibited melanization in vitro when dopa was used as a precursor. Addition of dopamine to the medium allowed melanization in the presence of the inhibitors. All these results indicate that dopamine is likely the primary precursor of cuticular melanin. The diphenoloxidase in the premelanin granules was activated in vivo between 19 and 21 h after HCS and was found to prefer dopamine to dopa and not to convert tyrosine to melanin. The activation of the prophenoloxidase was inhibited by 20-hydroxyecdysone (20-HE), both in vivo and in vitro, if hormone was given by 16 h after HCS. Infusion of 1.2 g/ml 20-HE into allatectomized larvae for 24 h from HCS prevented both the increase in DDC activity and the activation of the premelanin granules. Although the larvae ecdysed after a 15 h delay, melanization never occurred.Abbreviations -MDH L-3-(3,4 dihydroxyphenyl)-2-hydrazine-methylpropionic acid - -FM-dopa R-S--fluoromethyl-dopa - DCC dopa decarboxylase - 20-HE 20-hydroxyecdysone - JH juvenile hormone - HCS head capsule slippage     

Exuviae eating: a nitrogen meal?

Many insects eat their cast cuticle (exuviae) after moulting. The functional significance of this behaviour has not been addressed experimentally. I tested the hypothesis that exuviae eating constitutes a meal, so the animal recycles its nitrogen content. Nitrogenous compounds (protein and chitin) are major components of the cuticle in Periplaneta americana, accounting for as much as 87% of the total weight. It was found that insects almost invariably ate their exuviae during their larval life. The frequency of the behaviour decreased in newly emerged adults and varied between the sexes, males eating their exuviae less frequently than females. This may be due to the extra nitrogen endowment which females need for reproduction. Aposymbiotic animals, which lack the supply of essential amino acids from endosymbiotic bacteria, always ate their exuviae regardless of sex. When animals were reared on different diets throughout their larval life protein level in the diet correlated with exuviae eating. Animals reared on a low protein diet showed the highest levels of exuviae eating; animals reared on a high protein diet showed the highest levels of exuviae rejection. Analysis of the frass produced after exuviae meals showed that over 58% of the nitrogen present in the exuviae was recycled. This demonstrated that cockroaches digested nitrogenous compounds contained in the cuticle. The possibility that the exuviae meal has other functions is discussed, although the evidence supports a nutritional role.     

Cost of shield defence for tortoise beetles (Coleoptera: Chrysomelidae)

Abstract.

• 1 Tortoise beetle larvae possess a shield composed of exuviae and faeces which functions as an effective defence against some invertebrate predators.
• 2 In the laboratory, Charidotella bicolor, Deloyala guttata and Chelymorpha cassidea larvae with their shields experimentally removed did not exhibit enhanced performance (i.e. decreased development time, increased body mass, or higher survival) compared to control larvae with shields intact.
• 3 Disturbance caused during shield removal did not adversely affect larvae because performance did not differ among controls (undisturbed larvae with intact shields), disturbance controls (shield removal simulated, but shield left in place), and larvae with shields removed.
• 4 Larvae without shields did not exhibit compensatory feeding to reconstruct the shield following its removal.
• 5 In a field experiment in which predators were excluded, larvae with shields removed did not develop faster than controls; in fact, survival was slightly reduced (10%) for larvae without shields and may have resulted from desiccation.
• 6 For slow-moving tortoise beetle larvae, the cost of bearing the shield is minimal. Thus, larval shields, composed of recycled waste products, provide an inexpensive mode of protection from some natural enemies.