The structure of insect cuticles

Discovery of entomopathogenic fungi across geographical regions in southern China on pine sawyer beetle Monochamus alternatus and implication for multi-pathogen vectoring potential of this beetle

Entomopathogen-based biocontrol is crucial for blocking the transmission of vector-borne diseases; however, few cross-latitudinal investigations of entomopathogens have been reported for vectors transmitting woody plant diseases in forest ecosystems. The pine sawyer beetle Monochamus alternatus is an important wood borer and a major vector transmitting pine wilt disease, facilitating invasion of the pinewood nematode Bursaphelenchus xylophilus (PWN) in China. Due to the limited geographical breadth of sampling regions, species diversity of fungal associates (especially entomopathogenic fungi) on M. alternatus adults and their potential ecological functions have been markedly underestimated. In this study, through traditional fungal isolation with morphological and molecular identification, 640 fungal strains (affiliated with 15 genera and 39 species) were isolated from 81 beetle cadavers covered by mycelia or those symptomatically alive across five regional populations of this pest in southern China. Multivariate analyses revealed significant differences in the fungal community composition among geographical populations of M. alternatus, presenting regionalized characteristics, whereas no significant differences were found in fungal composition between beetle genders or among body positions. Four region-representative fungi, namely, Lecanicillium attenuatum (Zhejiang), Aspergillus austwickii (Sichuan), Scopulariopsis alboflavescens (Fujian), and A. ruber (Guangxi), as well as the three fungal species Beauveria bassiana, Penicillium citrinum, and Trichoderma dorotheae, showed significantly stronger entomopathogenic activities than other fungi. Additionally, insect-parasitic entomopathogenic fungi (A. austwickii, B. bassiana, L. attenuatum, and S. alboflavescens) exhibited less to no obvious phytopathogenic activities on the host pine Pinus massoniana, whereas P. citrinum, Purpureocillium lilacinum, and certain species of Fusarium spp.-isolated from M. alternatus body surfaces-exhibited remarkably higher phytopathogenicity. Our results provide a broader view of the entomopathogenic fungal community on the vector beetle M. alternatus, some of which are reported for the first time on Monochamus spp. in China. Moreover, this beetle might be more highly-risk in pine forests than previously considered, as a potential multi-pathogen vector of both PWN and phytopathogenic fungi.

Determination of Chitin Content in Insects: An Alternate Method Based on Calcofluor Staining

Chitin is an aminopolysaccharide present in yeast cells and arthropod cuticle and is one of the most abundant biopolymers. The conventional methods for the quantitation of chitin content in biological samples are based on its hydrolysis (acid or enzymatic), and the assessment of the byproduct, glucosamine. However, previously described methodologies are time-consuming, laborious, low throughput, and not applicable to insect samples in many cases. Here we describe a new approach to chitin content quantitation based on calcofluor fluorescent brightener staining of samples, followed by microplate fluorescence readings. Calcofluor is a specific chitin stain commonly used for topological localization of the polymer. The protocol was tested in three important disease vector species, namely Lutzomyia longipalpis, Aedes aegypti, and Rhodnius prolixus, and then compared to a classic colorimetric chitin assessment method. Results show that chitin content in the tested insects can vary largely in a range of 8–4600 micrograms of chitin per insect, depending on species, sex, and instar. Comparisons between measurements from the previous protocol and calcofluor method showed statistically significant differences in some samples. However, the difference might be due to interference in the classic method from non-chitin sources of glucosamine and reducing agents. Furthermore, chitinase hydrolysis reduces the total chitin mass estimated between 36 and 74%, consolidating the fluorescent measurements as actual stained chitin in the same extent that was observed with the standard protocol. Therefore, the calcofluor staining method revealed to be a fast and reliable technique for chitin quantitation in homogenized insect samples.

Water vapor absorption allows for volume expansion during molting in Armadillidiumvulgare and Porcelliodilatatus (Crustacea, Isopoda, Oniscidea)

Arthropods require periodic molting in order to grow which presents a number of challenges to terrestrial taxa. Following ecdysis, the pliant new cuticle is susceptible to buckling under gravity and requires elevated hydrostatic pressure for support. Terrestrial species also require a mechanism of volume expansion and stretching of the integument prior to sclerotization, a need that is readily met in aquatic arthropods by drinking. Options for land arthropods include drinking of dew, swallowing of air, or using muscular contractions to inflate air sacs in tracheate taxa. In this study we tested the hypothesis that crinochete terrestrial isopods (Isopoda: Oniscidea: Crinocheta) exploit their capacity for active water vapor absorption (WVA) to increase volume during molting. Two crinochete species, Armadillidiumvulgare and Porcelliodilatatus, were studied and compared with the non-absorbing species Ligidiumlapetum (Oniscidea: Ligiamorpha). Pre-molting animals were identified by sternal CaCO₃ deposits and exposed to 100% or 97% relative humidity (RH). Mass-changes were monitored by daily weighing and the timing of the posterior and anterior ecdyses was used to categorize time (days premolt and days post-molt) over the molt cycle. In each treatment RH, A.vulgare and P.dilatatus showed a progressive mass increase from 5 days premolt until the posterior or anterior ecdysis, followed abruptly by period of mass-loss lasting 3–4 days post-molt. The fact that the initial mass-gain is seen in 97 % RH, a humidity below the water activity of the hemolymph, confirms the role of WVA. Similarly, since the post-molt mass-loss is seen in 100 % RH, this must be due to active expulsion of water, possibly via maxillary urine. Concurrent changes in hemolymph osmolality were monitored in a separate batch of A.vulgare and show sustained osmolality during premolt and an abrupt decrease between the anterior and posterior ecdysis. These patterns indicate a mobilization of sequestered electrolytes during premolt, and a loss of electrolytes during the post-molt mass-loss, amounting to approximately 8.6 % of total hemolymph solutes. WVA, in conjunction with pulses of elevated hemolymph pressure, provides an efficient mechanism of pre-molt volume expansion prior to and during the biphasic molt in these species. Premolt Ligidiumlapetum exposed to same treatments failed to molt successfully and no premolt animals survived to day 3 (72 h) even in 100 % RH. The apparent dependence of this species on liquid water for successful molting could explain its obligatory association with riparian fringe habitats.

A massive incorporation of microbial genes into the genome of Tetranychus urticae, a polyphagous arthropod herbivore

A number of horizontal gene transfers (HGTs) have been identified in the spider mite Tetranychus urticae, a chelicerate herbivore. However, the genome of this mite species has at present not been thoroughly mined for the presence of HGT genes. Here, we performed a systematic screen for HGT genes in the T. urticae genome using the h-index metric. Our results not only validated previously identified HGT genes but also uncovered 25 novel HGT genes. In addition to HGT genes with a predicted biochemical function in carbohydrate, lipid and folate metabolism, we also identified the horizontal transfer of a ketopantoate hydroxymethyltransferase and a pantoate β-alanine ligase gene. In plants and bacteria, both genes are essential for vitamin B5 biosynthesis and their presence in the mite genome strongly suggests that spider mites, similar to Bemisia tabaci and nematodes, can synthesize their own vitamin B5. We further show that HGT genes were physically embedded within the mite genome and were expressed in different life stages. By screening chelicerate genomes and transcriptomes, we were able to estimate the evolutionary histories of these HGTs during chelicerate evolution. Our study suggests that HGT has made a significant and underestimated impact on the metabolic repertoire of plant-feeding spider mites.

The Evolution and Metamorphosis of Arthropod Proteomics and Genomics

This article presents an overview of the development of techniques for analyzing cuticular proteins (CPs), their transcripts, and their genes over the past 50 years based primarily on experience in the laboratory of J.H. Willis. It emphasizes changes in the kind of data that can be gathered and how such data provided insights into the molecular underpinnings of insect metamorphosis and cuticle structure. It describes the techniques that allowed visualization of the location of CPs at both the anatomical and intracuticular levels and measurement of the appearance and deployment of transcripts from CP genes as well as what was learned from genomic and transcriptomic data. Most of the early work was done with the cecropia silkmoth, Hyalophora cecropia, and later work was with Anopheles gambiae.

The structure and dynamics of chitin nanofibrils in an aqueous environment revealed by molecular dynamics simulations

The structure–property relations reveal the typical size of chitin nanofibrils observed in natural systems.

Ordering of protein and water molecules at their interfaces with chitin nano-crystals

Synchrotron X-ray diffraction was applied to study the structure of biogenic α-chitin crystals composing the tendon of the spider Cupiennius salei. Measurements were carried out on pristine chitin crystals stabilized by proteins and water, as well as after their deproteinization and dehydration. We found substantial shifts (up to Δq/q=9% in the wave vector in q-space) in the (020) diffraction peak position between intact and purified chitin samples. However, chitin lattice parameters extracted from the set of reflections (hkl), which did not contain the (020)-reflection, showed no systematic variation between the pristine and the processed samples. The observed shifts in the (020) peak position are discussed in terms of the ordering-induced modulation of the protein and water electron density near the surface of the ultra-thin chitin fibrils due to strong protein/chitin and water/chitin interactions. The extracted modulation periods can be used as a quantitative parameter characterizing the interaction length.

Decrease in fruit moisture content heralds and might launch the onset of ripening processes

It is known that fruit ripening is a genetically programmed event but it is not entirely clear what metabolic cue(s) stimulate the onset of ripening, ethylene action notwithstanding. Here, we examined the conjecture that fruit ripening might be evoked by an autonomously induced decrease in tissue water status. We found decline in water content occurring at the onset of ripening in climacteric and nonclimacteric fruit, suggesting that this phenomenon might be universal. This decline in water content persisted throughout the ripening process in some fruit, whereas in others it reversed during the progression of the ripening process. Applied ethylene also induced a decrease in water content in potato (Solanum tuberosum) tubers. In ethylene-mutant tomato (Solanum lycopersicum) fruit (antisense to1-aminocyclopropane carboxylate synthase), cold-induced decline in water content stimulated onset of ripening processes apparently independently of ethylene action, suggesting cause-and-effect relationship between decreasing water content and onset of ripening. The decline in tissue water content, occurring naturally or induced by ethylene, was strongly correlated with a decrease in hydration (swelling) efficacy of cell wall preparations suggesting that hydration dynamics of cell walls might account for changes in tissue moisture content. Extent of cell wall swelling was, in turn, related to the degree of oxidative cross-linking of wall-bound phenolic acids, suggesting that oxidant-induced wall restructuring might mediate cell wall and, thus, fruit tissue hydration status. We propose that oxidant-induced cell wall remodeling and consequent wall dehydration might evoke stress signaling for the onset of ripening processes.

PRACTICAL APPLICATION

This study suggests that decline in fruit water content is an early event in fruit ripening. This information may be used to gauge fruit maturity for appropriate harvest date and for processing. Control of fruit hydration state might be used to regulate the onset of fruit ripening.

Lack of phenotypic and evolutionary cross-resistance against parasitoids and pathogens in Drosophila melanogaster

Background

When organisms are attacked by multiple natural enemies, the evolution of a resistance mechanism to one natural enemy will be influenced by the degree of cross-resistance to another natural enemy. Cross-resistance can be positive, when a resistance mechanism against one natural enemy also offers resistance to another; or negative, in the form of a trade-off, when an increase in resistance against one natural enemy results in a decrease in resistance against another. Using Drosophila melanogaster, an important model system for the evolution of invertebrate immunity, we test for the existence of cross-resistance against parasites and pathogens, at both a phenotypic and evolutionary level.

Methods

We used a field strain of D. melanogaster to test whether surviving parasitism by the parasitoid Asobara tabida has an effect on the resistance against Beauveria bassiana, an entomopathogenic fungus; and whether infection with the microsporidian Tubulinosema kingi has an effect on the resistance against A. tabida. We used lines selected for increased resistance to A. tabida to test whether increased parasitoid resistance has an effect on resistance against B. bassiana and T. kingi. We used lines selected for increased tolerance against B. bassiana to test whether increased fungal resistance has an effect on resistance against A. tabida.

Results/Conclusions

We found no positive cross-resistance or trade-offs in the resistance to parasites and pathogens. This is an important finding, given the use of D. melanogaster as a model system for the evolution of invertebrate immunity. The lack of any cross-resistance to parasites and pathogens, at both the phenotypic and the evolutionary level, suggests that evolution of resistance against one class of natural enemies is largely independent of evolution of resistance against the other.

Species-specific shells: Chitin synthases and cell mechanics in molluscs

The size, morphology and species-specific texture of mollusc shell biominerals is one of the unresolved questions in nature. In search of molecular control principles, chitin has been identified by Weiner and Traub (FEBS Lett. 1980, 111:311–316) as one of the organic compounds with a defined co-organization with mineral phases. Chitin fibers can be aligned with certain mineralogical axes of crystalline calcium carbonate in a species-specific manner. These original observations motivated the functional characterization of chitin forming enzymes in molluscs. The full-length cDNA cloning of mollusc chitin synthases identified unique myosin domains as part of the biological control system. The potential impact of molecular motors and other conserved domains of these complex transmembrane enzymes on the evolution of shell biomineralization is investigated and discussed in this article.

A possible structural model of members of the CPF family of cuticular proteins implicating binding to components other than chitin

The physical properties of cuticle are determined by the structure of its two major components, cuticular proteins (CPs) and chitin, and, also, by their interactions. A common consensus region (extended R&R Consensus) found in the majority of cuticular proteins, the CPRs, binds to chitin. Previous work established that beta-pleated sheet predominates in the Consensus region and we proposed that it is responsible for the formation of helicoidal cuticle. Remote sequence similarity between CPRs and a lipocalin, bovine plasma retinol binding protein (RBP), led us to suggest an antiparallel beta-sheet half-barrel structure as the basic folding motif of the R&R Consensus. There are several other families of cuticular proteins. One of the best defined is CPF. Its four members in Anopheles gambiae are expressed during the early stages of either pharate pupal or pharate adult development, suggesting that the proteins contribute to the outer regions of the cuticle, the epi- and/or exo-cuticle. These proteins did not bind to chitin in the same assay used successfully for CPRs. Although CPFs are distinct in sequence from CPRs, the same lipocalin could also be used to derive homology models for one A. gambiae and one Drosophila melanogaster CPF. For the CPFs, the basic folding motif predicted is an eight-stranded, antiparallel beta-sheet, full-barrel structure. Possible implications of this structure are discussed and docking experiments were carried out with one possible Drosophila ligand, 7(Z),11(Z)-heptacosadiene.

The dynamics of nacre self-assembly

We show how nacre and pearl construction in bivalve and gastropod molluscs can be understood in terms of successive processes of controlled self-assembly from the molecular- to the macro-scale. This dynamics involves the physics of the formation of both solid and liquid crystals and of membranes and fluids to produce a nanostructured hierarchically constructed biological composite of polysaccharides, proteins and mineral, whose mechanical properties far surpass those of its component parts.

Retroactive, a membrane-anchored extracellular protein related to vertebrate snake neurotoxin-like proteins, is required for cuticle organization in the larva of Drosophila melanogaster

Mutations in the rtv gene cause disarrangement of chitin fibers in the cuticle of the Drosophila larva, and occasionally the cuticle detaches from the epidermis. We have identified the rtv gene, and using the new HHpred homology detection method, we show that the Rtv protein defines a new family of disulfide-rich proteins in insects that are related to vertebrate snake neurotoxin-like proteins, including CD59 and transforming growth factor-beta type II receptors. Rtv is an extracellular membrane-anchored protein exposing six aromatic residues that may mediate binding to chitin. We propose that this binding function of Rtv may assist the organization of chitin fibers at the epidermal cell surface during cuticle assembly.

Unique features of the structural model of 'hard' cuticle proteins: implications for chitin-protein interactions and cross-linking in cuticle

Cuticular proteins are one of the determinants of the physical properties of cuticle. A common consensus region (extended R&R Consensus) in these proteins binds to chitin, the other major component of cuticle. We previously predicted the preponderance of beta-pleated sheet in the consensus region and proposed its responsibility for the formation of helicoidal cuticle (Iconomidou et al., Insect Biochem. Mol. Biol. 29 (1999) 285). Subsequently, we verified experimentally the abundance of antiparallel beta-pleated sheet in the structure of cuticle proteins (Iconomidou et al., Insect Biochem. Mol. Biol. 31 (2001) 877). Homology modelling of soft (RR-1) cuticular proteins using bovine plasma retinol binding protein (RBP) as a template revealed an antiparallel beta-sheet half-barrel structure as the basic folding motif (Hamodrakas et al., Insect Biochem. Molec. Biol. 32 (2002) 1577). The RR-2 proteins characteristic of hard cuticle, have a far more conserved consensus and frequently more histidine residues. Extension of modelling to this class of consensus, in this work, reveals in detail several unique features of the proposed structural model to serve as a chitin binding structural motif, thus providing the basis for elucidating cuticle's overall architecture and chitin-protein interactions in cuticle.

Costs of resistance in insect-parasite and insect-parasitoid interactions

Most, if not all, organisms face attack by natural enemies and will be selected to evolve some form of defence. Resistance may have costs as well as its obvious benefits. These costs may be associated with actual defence or with the maintenance of the defensive machinery irrespective of whether a challenge occurs. In this paper, the evidence for costs of resistance in insect-parasite and insect-parasitoid systems is reviewed, with emphasis on two host-parasitoid systems, based on Drosophila melanogaster and pea aphids as hosts. Data from true insect-parasite systems mainly concern the costs of actual defence; evidence for the costs of standing defences is mostly circumstantial. In pea aphids, the costs of standing defences have so far proved elusive. Resistance amongst clones is not correlated with life-time fecundity, whether measured on good or poor quality plants. Successful defence by a D. melanogaster larva results in a reduction in adult size and fecundity and an increased susceptibility to pupal parasitoids. Costs of standing defences are a reduction in larval competitive ability though these costs only become important when food is limited. It is concluded that costs of resistance can play a pivotal role in the evolutionary and population dynamic interactions between hosts and their parasites.

A structural model of the chitin-binding domain of cuticle proteins

The nature of the interaction of insect cuticular proteins and chitin is unknown even though about half of the cuticular proteins sequenced thus far share a consensus region that has been predicted to be the site of chitin binding. We previously predicted the preponderance of beta-pleated sheet in the consensus region and proposed its responsibility for the formation of helicoidal cuticle (Iconomidou et al., Insect Biochem. Mol. Biol. 29 (1999) 285). Consequently, we have also verified experimentally the abundance of antiparallel beta-pleated sheet in the structure of cuticle proteins (Iconomidou et al., Insect Biochem. Mol. Biol. 31 (2001) 877). In this work, based on sequence and secondary structure similarity of cuticle proteins, and especially that of the consensus motif, to that of bovine plasma retinol binding protein (RBP), we propose by homology modelling an antiparallel beta-sheet half-barrel structure as the basic folding motif of cuticle proteins. This folding motif may provide the template for elucidating cuticle protein-chitin interactions in detail and reveal the precise geometrical formation of cuticle's helicoidal architecture. This predicted motif is another example where nature utilizes an almost flat protein surface covered by aromatic side chains to interact with the polysaccharide chains of chitin.

"Soft"-cuticle protein secondary structure as revealed by FT-Raman, ATR FT-IR and CD spectroscopy

The nature of the interaction of insect cuticular proteins and chitin is unknown even though about half of the cuticular proteins sequenced thus far share a consensus region that has been predicted to be the site of chitin binding. We previously predicted the preponderance of a beta-pleated sheet in the consensus region and proposed its responsibility for the formation of helicoidal cuticle (Iconomidou et al., Insect Biochem. Mol. Biol. 29 (1999) 285). In this study, we examined experimentally the secondary structure of intact and guanidine hydrochloride extracted cuticle and the cuticular protein extract. The studied cuticle came from the larval dorsal abdomen of the lepidopteran Hyalophora cecropia, a classical example of "soft" cuticle. Analysis with FT-Raman, ATR FT-IR and CD spectroscopy indicates that antiparallel beta-pleated sheet is the predominant molecular conformation of "soft-cuticle" proteins both in situ in the cuticle and following extraction. It seems that this conformation dictates the modes of chitin-protein interaction in cuticle, in agreement with earlier proposals (Atkins, J. Biosci. 8 (1985) 375).

Geographic Patterns in the Evolution of Resistance and Virulence in Drosophila and Its Parasitoids

Many insects are attacked by internal parasitoids against which they mount a largely cellular immunological defense. The resistance of a host and the virulence of a parasitoid determine which species survives after parasitism. Drosophila is parasitized by several hymenopterous parasitoids, especially those in the genera Asobara and Leptopilina. Geographic patterns have been found in parasitoid virulence and host resistance, the clearest of which is a cline in Asobara tabida virulence from the north (low) to the south (high) of Europe. Drosophila melanogaster resistance is highest in central-southern Europe and lower elsewhere. We review and interpret these patterns in the light of recent experimental and theoretical studies of the evolution and coevolution of these traits. We find no evidence for genotype-specific virulence and defense, which makes "Red Queen"-type coevolution unlikely. The most important explanation for the patterns is geographic differences in host-parasitoid community structure. Asobara tabida virulence is positively correlated with the resistance of its main hosts, and there is more limited evidence that D. melanogaster resistance is influenced by the virulence of its parasitoids. We critically appraise whether the evidence available so far supports a coevolutionary explanation for the levels of these traits.

Is beta-pleated sheet the molecular conformation which dictates formation of helicoidal cuticle?

Over 100 sequences for cuticular proteins are now available, but there have been no formal analyses of how these sequences might contribute to the helicoidal architecture of cuticle or to the interaction of these proteins with chitin. A secondary structure prediction scheme (Hamodrakas, S.J., 1988. A protein secondary structure prediction scheme for the IBM PC and compatibles. CABIOS 4, 473-477) that combines six different algorithms predicting alpha-helix, beta-strands and beta-turn/loops/coil has been used to predict the secondary structure of chorion proteins and experimental confirmation has established its utility (Hamodrakas, S.J., 1992. Molecular architecture of helicoidal proteinaceous eggshells. In: Case, S.T. (Ed.), Results and Problems in Cell Differentiation, Vol. 19, Berlin-Heidelberg, Springer Verlag, pp. 116-186 and references therein). We have used this same scheme with eight cuticular protein sequences associated with hard cuticles and nineteen from soft cuticles. Secondary structure predictions were restricted to a conserved 68 amino acid region that begins with a preponderance of hydrophilic residues and ends with a 33 amino acid consensus region, first identified by Rebers and Riddiford (Rebers, J.F., Riddiford, L.M., 1988. Structure and expression of a Manduca sexta larval cuticle gene homologous to Drosophila cuticle genes. J. Mol. Biol. 203, 411-423). Both classes of sequences showed a preponderance of beta-pleated sheet, with four distinct strands in the proteins from 'hard' cuticles and three from 'soft'. In both cases, tyrosine and phenylalanine were found on one face within a sheet, an optimal location for interaction with chitin. We propose that this beta-sheet dictates formation of helicoidal cuticle.

Adsorbed layers: the stimulus to settlement in barnacles

The factor responsible for inducing settlement in cyprids ofBalanus balanoides(L.) can be fractionated by ammonium sulphate, and gives positive reactions to a series of tests identifying it with arthropodin, the water soluble protein fraction of arthropod cuticle. Solutions of the settling factor have little effect on the behaviour of cyprids exploring a surface, and do not promote settlement. Slate surfaces previously soaked in a dilute seawater extract of the settling factor can be distinguished by cyprids from freshly cleaned slates, even when cyprids and both surfaces are freshly immersed in the same extract that was previously used to soak the first set of slates. It is argued from this that the cyprids must respond to a specific molecular configuration manifested by the protein only when physically or chemically bound to a surface. Since in nature cyprids respond to a surface consisting of protein tanned by the natural polyphenols of the epicuticle (sclerotin), we consider that in our laboratory experiments with adsorbed layers of soluble arthropodin they respond to the same molecular configuration at the surface. Such recognition of specific molecular groupings of an insoluble material involves a truly contact chemical sense, which we have called a ‘tactile chemical sense’. This facility may exist in other animals. The settlement behaviour of barnacle cyprids is analyzed in terms of instinctive behaviour.

On the structure of the antennular attachment organ of the cypris larva of Balanus balanoides (L.)

The third segment of the antennule of the cypris larva of Balanus balanoides is modified as an attachment organ with a disk by which the cyprid attaches to submerged surfaces. The attachment disk is covered with a felt of fine cuticular villi. Opening on to the disk are terminal branches of the cement duct, numerous glands and an array of sensory hairs. The sensory structures are arthropod scolopidia with the dendrites giving rise to cilia which, distally, change to distal sensory processes. It is suggested that the cuticular hairs situated in invaginations of the cuticle around the margin of the disk function as position receptors and that the two setae lying away from the cuticle of the segment are mechanoreceptors. Three of the scolopidia have structures suiting them for chemoreception; the distal sensory processes are exposed to the exterior at the tip of the hair. Two of these hairs are positioned at the margin and one at the centre of the disk. The fourth segment, which arises from the side of the attachment organ, is packed with sensory cell processes which are associated with setae arising at the distal end; its movements are controlled by a single muscle from the third segment. A suction mechanism of adhesion is precluded as there are no structures which could effect or release suction beneath the disk. The disk could act as an adhesive pad, with the cuticular villi increasing its surface area and the antennular glands possibly secreting a viscous substance. The presence of chemoreceptors on the attachment organ indicates that a chemosensory mechanism could operate during the gregarious behaviour of settling cyprids.

Biology and physics of locust flight. V. Strength and elasticity of locust cuticle

Elastic deformations of the cuticle play a major role in the energetics of flying locusts but the literature provides no relevant information about the elastic properties of any arthropod cuticle. The results are therefore discussed both in relation to locust flight and in relation to strength and elasticity of organic materials in general. InSchistocerca gregariaForskal there are two types of elastic cuticle, ordinarysolid cuticleandrubber-like cuticle. The characteristic material in the latter type is a newly discovered protein rubber,resilin. Samples of both were studied under static and dynamic conditions. The tensile properties of solid cuticle from various parts of the body (hind tibia, pleural wall, forewing) are similar to those of oak wood and of synthetic resins reinforced with cellulose; the static coefficient of elasticity (dcr/de) is 800 to 1000 kg/mm2and the tensile strength 8 to 10 kg/mm2, corresponding to an ultimate extension of 2 to 3 %. At moderate loads, the tensile and compressive moduli are of equal magnitude, but it is argued that the effect of tanning (hardening) is to increase the compressive strength and modulus rather than the tensile properties. Static loading results in lasting deformation. The dynamic modulus is of the same magnitude as the static modulus (forewing), at least up to 5 kg mm-2s-1and, provided the tension does not exceed 0-5 kg/mm2, the loss factor is less than 0.1. The rubber-like sample (prealar arm) consists of parallel lamellae of chitin (0.2μ thick) glued together by sheets of resilin (about 3μ thick). It behaves like a solid when extended in the direction of the lamellae but otherwise like a rubber, the elastic modulus being 0.2 kg/mm2. The swelling pressure of resilin does not play any direct role but swelling alters the geometry and, to a small extent, the elastic modulus. It is suggested that the animal controls the stiffness of its rubber-like structures by altering the swelling equilibrium chemically which, in a model experiment, is done by blocking the free amino groups. Rubber-like cuticle does not encounter any permanent deformation which is attributed to the known lack of flow of pure resilin. Within the biological rate of deformation (up to 6 unit lengths per second), the dynamic stiffness remains within 4 % of the static value and the loss factor is only 0.03, i.e. less than for other natural or synthetic rubbers. A three-component model of arthropod cuticle is suggested. It accounts for the enormous differences in mechanical properties between adjacent parts and also for the fact that strict structural and developmental continuity is observed between the parts. It has three components: (1) crystalline chitin, (2) a rubber-like protein which may act as a deformable matrix and which entraps, (3) water-soluble proteins which can undergo proper tanning.

Pupal and larval cuticle proteins of Drosophila melanogaster

Proteins, soluble in 7 M urea, were extracted from third-instar larval and pupal cuticles of Drosophila melanogaster. Both extracts contain a limited number of polypeptides resolved by one- or two-dimensional electrophoresis. The five major larval proteins have low molecular weights (less than 20000) and are not glycosylated. The major pupal cuticle proteins fall into two size classes: two with apparent molecular weights of 56K and 82K and four with molecular weights between 15K and 25K. The proteins with high apparent molecular weights are glycosylated. In nondenaturing gels, no components of the larval and pupal cuticle extracts comigrate. One-dimensional "fingerprints" indicate that cuticle proteins from these two stages have unique primary structures. Immunological results indicate that the major low molecular weight larval and pupal cuticle proteins are comprised of two families of proteins that share antigenic determinants. The high molecular weight pupal cuticle proteins are immunologically unrelated to the low molecular weight components. We conclude that the pupal and larval proteins are encoded in part by multigene families that have arisen by gene duplication and evolutionary divergence.

Increased rate of melanization in hemolymph of American cockroaches (Periplaneta americana) and house crickets (Acheta domesticus) intoxicated by insecticides

Treatment of house crickets and American cockroaches with any one of a variety of insecticides increased the rate of melanization in hemolymph incubated with diphenol substrates.

FREE AMINO ACIDS IN THE HAEMOLYMPH OF RHODNIUS PROLIXUS STÅHL (HEMIPTERA: REDUVIIDAE)

Nineteen free amino acids and four ninhydrin-positive compounds were detected in the haemolymph of fifth-instar nymphs of Rhodnius prolixus by the technique of thin-layer chromatography. On the sixth day after feeding, tyrosine and tryptophan appeared in the haemolymph. Their concentration increased until the 12th day when testing stopped. The concentrations of alanine, asparagine, cystine, isoleucine, phenylalanine, and threonine fluctuated moderately from day to day. The results obtained by thin-layer chromatography differed from those of a similar study in which the technique of paper chromatography was used.