Osiris gene family defines the cuticle nanopatterns of Drosophila

Nanostructures of pores and protrusions in the insect cuticle modify molecular permeability and surface wetting and help insects sense various environmental cues. However, the cellular mechanisms that modify cuticle nanostructures are poorly understood. Here, we elucidate how insect-specific Osiris family genes are expressed in various cuticle-secreting cells in the Drosophila head during the early stages of cuticle secretion and cover nearly the entire surface of the head epidermis. Furthermore, we demonstrate how each sense organ cell with various cuticular nanostructures expressed a unique combination of Osiris genes. Osiris gene mutations cause various cuticle defects in the corneal nipples and pores of the chemosensory sensilla. Thus, our study emphasizes on the importance of Osiris genes for elucidating cuticle nanopatterning in insects.

The origins of colour patterns in fossil insects revealed by maturation experiments

Many fossil insects show monochromatic colour patterns that may provide valuable insights into ancient insect behaviour and ecology. Whether these patterns reflect original pigmentary coloration is, however, unknown, and their formation mechanism has not been investigated. Here, we performed thermal maturation experiments on extant beetles with melanin-based colour patterns. Scanning electron microscopy reveals that melanin-rich cuticle is more resistant to degradation than melanin-poor cuticle: with progressive maturation, melanin-poor cuticle regions experience preferential thinning and loss, yet melanin-rich cuticle remains. Comparative analysis of fossil insects with monotonal colour patterns confirms that the variations in tone correspond to variations in preserved cuticle thickness. These preserved colour patterns can thus be plausibly explained as melanin-based patterning. Recognition of melanin-based colour patterns in fossil insects opens new avenues for interpreting the evolution of insect coloration and behaviour through deep time.

Cuticular profiling of insecticide resistant Aedes aegypti

Insecticides have made great strides in reducing the global burden of vector-borne disease. Nonetheless, serious public health concerns remain because insecticide-resistant vector populations continue to spread globally. To circumvent insecticide resistance, it is essential to understand all contributing mechanisms. Contact-based insecticides are absorbed through the insect cuticle, which is comprised mainly of chitin polysaccharides, cuticular proteins, hydrocarbons, and phenolic biopolymers sclerotin and melanin. Cuticle interface alterations can slow or prevent insecticide penetration in a phenomenon referred to as cuticular resistance. Cuticular resistance characterization of the yellow fever mosquito, Aedes aegypti, is lacking. In the current study, we utilized solid-state nuclear magnetic resonance spectroscopy, gas chromatography/mass spectrometry, and transmission electron microscopy to gain insights into the cuticle composition of congenic cytochrome P450 monooxygenase insecticide resistant and susceptible Ae. aegypti. No differences in cuticular hydrocarbon content or phenolic biopolymer deposition were found. In contrast, we observed cuticle thickness of insecticide resistant Ae. aegypti increased over time and exhibited higher polysaccharide abundance. Moreover, we found these local cuticular changes correlated with global metabolic differences in the whole mosquito, suggesting the existence of novel cuticular resistance mechanisms in this major disease vector.

Triazine Herbicide and NPK Fertilizer Exposure: Accumulation of Heavy Metals and Rare Earth Elements, Effects on Cuticle Melanization, and Immunocompetence in the Model Species Tenebrio molitor

The increasing use of agrochemicals, including fertilizers and herbicides, has led to worrying metal contamination of soils and waters and raises serious questions about the effects of their transfer to different levels of the trophic web. Accumulation and biomagnification of essential (K, Na, Mg, Zn, Ca), nonessential (Sr, Hg, Rb, Ba, Se, Cd, Cr, Pb, As), and rare earth elements (REEs) were investigated in newly emerged adults of Tenebrio molitor exposed to field-admitted concentrations of a metribuzin-based herbicide and an NPK blend fertilizer. Chemical analyses were performed using inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) supported by unsupervised pattern recognition techniques. Physiological parameters such as cuticle melanization, cellular (circulating hemocytes), and humoral (phenoloxidase enzyme activity) immune responses and mass loss were tested as exposure markers in both sexes. The results showed that NPK fertilizer application is the main cause of REE accumulation in beetles over time, besides toxic elements (Sr, Hg, Cr, Rb, Ba, Ni, Al, V, U) also present in the herbicide-treated beetles. The biomagnification of Cu and Zn suggested a high potential for food web transfer in agroecosystems. Gender differences in element concentrations suggested that males and females differ in element uptake and excretion. Differences in phenotypic traits show that exposure affects metabolic pathways involving sequestration and detoxification during the transition phase from immature-to-mature beetles, triggering a redistribution of resources between sexual maturation and immune responses. Our findings highlight the importance of setting limits for metals and REEs in herbicides and fertilizers to avoid adverse effects on species that provide ecosystem services and contribute to soil health in agroecosystems.

Cuticular profiling of insecticide resistant Aedes aegypti

Insecticides have made great strides in reducing the global burden of vector-borne disease. Nonetheless, serious public health concerns remain because insecticide-resistant vector populations continue to spread globally. To circumvent insecticide resistance, it is essential to understand all contributing mechanisms. Contact-based insecticides are absorbed through the insect cuticle, which is comprised mainly of chitin polysaccharides, cuticular proteins, hydrocarbons, and phenolic biopolymers sclerotin and melanin. Cuticle interface alterations can slow or prevent insecticide penetration in a phenomenon referred to as cuticular resistance. Cuticular resistance characterization of the yellow fever mosquito, Aedes aegypti , is lacking. In the current study, we utilized solid-state Nuclear Magnetic Resonance (ssNMR) spectroscopy, gas chromatography/mass spectrometry (GC-MS), and transmission electron microscopy (TEM) to gain insights into the cuticle composition of congenic cytochrome P450 monooxygenase insecticide resistant and susceptible Ae. aegypti . No differences in cuticular hydrocarbon content or phenolic biopolymer deposition were found. In contrast, we observed cuticle thickness of insecticide resistant Ae. aegypti increased over time and exhibited higher polysaccharide abundance. Moreover, we found these local cuticular changes correlated with global metabolic differences in the whole mosquito, suggesting the existence of novel cuticular resistance mechanisms in this major disease vector.

Abnormal Antennal Olfactory Sensilla Phenotypes Involved in Olfactory Deficit in Bactrocera correcta (Diptera: Tephritidae)

Simple Summary

Tephritidae fruit flies sense odorants mainly through antennal olfactory sensilla with nanopores. Therefore, theoretically, the development of nanopore-targeted pest control technologies is an important direction in the future. Here, we report naturally occurring abnormal antennal trichoid and basiconic olfactory sensilla phenotypes consisting of abnormal bulges and reduced nanopore numbers in a long-term laboratory rearing colony of the guava fruit fly Bactrocera correcta, and further find that the reduction of nanopore numbers in these sensilla led to an olfactory deficit. Our findings provide a basis for developing nanopore-targeted pest control technologies in the future.

Abstract

The guava fruit fly, Bactrocera correcta, is one of the most destructive pests in the genus Bactrocera and detects environmental odorants mainly through antennal olfactory sensilla phenotypes with nanopores. However, it is unclear whether there are naturally occurring abnormal antennal olfactory sensilla phenotypes that affect olfaction. Here, we found that there were abnormal bulges besides nanopores on the surface of trichoid and basiconic olfactory sensilla in the antennal flagellum of long-term laboratory rearing colony (LTC), and that nanopore number in these olfactory sensilla was also remarkably reduced. Notably, the electroantennogram (EAG) responses of LTC insects to methyl eugenol or β-caryophyllene were inhibited, and their behavioral responses elicited by the same odorants were also impaired. These results revealed naturally occurring abnormal antennal olfactory sensilla phenotypes which were involved in olfactory deficit in B. correcta, providing a platform to further study nanopore-targeted pest control technologies in the future.

Optical inactivation of a proprioceptor in an insect by non-genetic tools

BACKGROUND

The specific role of sensory organs in locomotor pattern generation is traditionally investigated by means of mechanical ablation in arthropods that currently do not allow genetic manipulation. Mechanical ablation is irreversible, and may lead to injury discharges and changes in the structural integrity of the cuticle.

NEW METHOD

Here, we present a new method to temporarily or permanently deprive parts of an insect nervous system of sensory feedback from leg proprioceptors by means of blue light application. We illuminated campaniform sensilla (CS) with a blue LED (420-480 nm) or a 473 nm laser at different light intensities to optically eliminate sensory and motor neuron responses to mechanical stimulation.

RESULTS

We were able to eliminate all stimulus-evoked responses of CS. Individual CS groups were precisely and selectively inactivated without affecting nearby proprioceptors, using an optical fiber (Ø 200 µm) to guide the light. Our results demonstrated that lower light intensities significantly increase the required exposure time, but also the chance for recovery, thus making the effect reversible.

COMPARISON WITH EXISTING METHODS

In contrast to mechanical ablation, optical inactivation of individual sensory organs is non-invasive and does not affect the behavioral state of the animal, nor does it induce escape behavior. This is especially relevant in non-model system experimental animals where optogenetic manipulation cannot be used, due to a lack of established methods of access.

CONCLUSION

Our results show that the proposed method is a reliable alternative to mechanical ablation and can be successfully applied to the CS, as it fulfills all requirements regarding selectivity, efficiency, and reproducibility.

Microstructural design for mechanical-optical multifunctionality in the exoskeleton of the flower beetle Torynorrhina flammea

Biological systems have a remarkable capability of synthesizing multifunctional materials that are adapted for specific physiological and ecological needs. When exploring structure-function relationships related to multifunctionality in nature, it can be a challenging task to address performance synergies, trade-offs, and the relative importance of different functions in biological materials, which, in turn, can hinder our ability to successfully develop their synthetic bioinspired counterparts. Here, we investigate such relationships between the mechanical and optical properties in a multifunctional biological material found in the highly protective yet conspicuously colored exoskeleton of the flower beetle, Torynorrhina flammea Combining experimental, computational, and theoretical approaches, we demonstrate that a micropillar-reinforced photonic multilayer in the beetle's exoskeleton simultaneously enhances mechanical robustness and optical appearance, giving rise to optical damage tolerance. Compared with plain multilayer structures, stiffer vertical micropillars increase stiffness and elastic recovery, restrain the formation of shear bands, and enhance delamination resistance. The micropillars also scatter the reflected light at larger polar angles, enhancing the first optical diffraction order, which makes the reflected color visible from a wider range of viewing angles. The synergistic effect of the improved angular reflectivity and damage localization capability contributes to the optical damage tolerance. Our systematic structural analysis of T. flammea's different color polymorphs and parametric optical and mechanical modeling further suggest that the beetle's microarchitecture is optimized toward maximizing the first-order optical diffraction rather than its mechanical stiffness. These findings shed light on material-level design strategies utilized in biological systems for achieving multifunctionality and could thus inform bioinspired material innovations.

Obtaining chitin, chitosan and their melanin complexes from insects

Interest in insects as a source of valuable biologically active substances has significantly increased over the past few years. Insects serve as an alternative source of chitin, which forms up to 40% of their exoskeleton. Chitosan, a deacetylated derivative of chitin, attracts the attention of scientists due to its unique properties (sorption, antimicrobial, film-forming, wound healing). Furthermore, some insect species are unique and can be used to obtain chitin- and chitosan-melanin complexes in the later stages of ontogenesis. Due to the synergistic effect, chitosan and melanin can enhance each other's biological activity, providing a wide range of potential applications.

Role of Surface Chemistry in the Superhydrophobicity of the Springtail Orchesella cincta (Insecta:Collembola)

Collembola are ancient arthropods living in soil with extensive exposure to dirt, bacteria, and fungi. To protect from the harsh environmental conditions and to retain a layer of air for breathing when submerged in water, they have evolved a superhydrophobic, liquid-repelling cuticle surface. The nonfouling and self-cleaning properties of springtail cuticle make it an interesting target of biomimetic materials design. Recent research has mainly focused on the intricate microstructures at the cuticle surface. Here we study the role of the cuticle chemistry for the Collembola species Orchesella cincta (Collembola, Entomobryidae). O. cincta uses a relatively simple cuticle structure with primary granules arranged to function as plastrons. In contrast to the Collembolan cuticle featuring structures on multiple length scales that is functional irrespective of surface chemistry, we found that the O. cincta cuticle loses its hydrophobic properties after being rinsed with dichloromethane. Sum frequency generation spectroscopy and time-of-flight secondary ion mass spectrometry in combination with high-resolution mass spectrometry show that a nanometer thin triacylglycerol-containing wax layer at the cuticle surface is essential for maintaining the antiwetting properties. Removal of the wax layer exposes chitin, terpenes, and lipid layers in the cuticle. With respect to biomimetic applications, the results show that, combined with a carefully chosen surface chemistry, superhydrophobicity may be achieved using a relatively unsophisticated surface structure rather than a complex, re-entrant surface structure alone.

Cuticle sclerotization determines the difference between the elastic moduli of locust tibiae

A striking characteristic of insect cuticle is the wide range of its material property values, with respect to stiffness, strength and toughness. The elastic modulus of cuticle, for instance, ranges over seven orders of magnitude in different structures and different species. Previous studies suggested that this characteristic is influenced by the microstructure and sclerotization of cuticle. However, the relative role of the two factors in determining the material properties of cuticle is unknown. Here we used a combination of scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and nanoindentation, to investigate the effect of microstructure and sclerotization on the elastic modulus of tibiae of desert locusts. Our results showed that tibial cuticle is an anisotropic material with the highest elastic modulus along the tibial axis. This is likely because majority of the fibers in the cuticle are oriented along this axis. We also found that the hind tibia has a significantly higher elastic modulus, compared with the fore and mid tibiae. This is likely due to the higher sclerotization level of the hind tibia cuticle, and seems to be an adaptation to the locust locomotion by jumping, in which axial loads in the hind tibiae may reach several times the insect body weight. Our results suggest that while sclerotization determines the difference between the elastic moduli of the tibiae, anisotropic properties of each tibia is controlled by the specific fiber orientation. Our study provides one of only a few comprehensive investigations on insect cuticle, and helps to better understand the structure-material-function relationship in this complex biological composite. STATEMENT OF SIGNIFICANCE: Insect cuticle is a biological composite with strong anisotropy and wide ranges of material properties. Using an example of the tibial cuticle of desert locusts, we examined the role of two influential factors on the elastic modulus of cuticle: microstructure and sclerotization. Our results suggested the strong influence of sclerotization on the variation of the elastic modulus among fore, mid and hind tibiae, and that of the microstructure on the anisotropy of each tibia. Our results deepens the current understanding of the structure-material-function relationship in complex insect cuticle.

Nanopore Formation in the Cuticle of an Insect Olfactory Sensillum

Nanometer-level patterned surface structures form the basis of biological functions, including superhydrophobicity, structural coloration, and light absorption [1-3]. In insects, the cuticle overlying the olfactory sensilla has multiple small (50- to 200-nm diameter) pores [4-8], which are supposed to function as a filter that admits odorant molecules, while preventing the entry of larger airborne particles and limiting water loss. However, the cellular processes underlying the patterning of extracellular matrices into functional nano-structures remain unknown. Here, we show that cuticular nanopores in Drosophila olfactory sensilla originate from a curved ultrathin film that is formed in the outermost envelope layer of the cuticle and secreted from specialized protrusions in the plasma membrane of the hair forming (trichogen) cell. The envelope curvature coincides with plasma membrane undulations associated with endocytic structures. The gore-tex/Osiris23 gene encodes an endosomal protein that is essential for envelope curvature, nanopore formation, and odor receptivity and is expressed specifically in developing olfactory trichogen cells. The 24-member Osiris gene family is expressed in cuticle-secreting cells and is found only in insect genomes. These results reveal an essential requirement for nanopores for odor reception and identify Osiris genes as a platform for investigating the evolution of surface nano-fabrication in insects.

Do drowning and anoxia kill head lice?

Chemical, physical, and mechanical methods are used to control human lice. Attempts have been made to eradicate head lice Pediculus humanus capitis by hot air, soaking in various fluids or asphyxiation using occlusive treatments. In this study, we assessed the maximum time that head lice can survive anoxia (oxygen deprivation) and their ability to survive prolonged water immersion. We also observed the ingress of fluids across louse tracheae and spiracle characteristics contrasting with those described in the literature. We showed that 100% of lice can withstand 8 h of anoxia and 12.2% survived 14 h of anoxia; survival was 48.9% in the untreated control group at 14 h. However, all lice had died following 16 h of anoxia. In contrast, the survival rate of water-immersed lice was significantly higher when compared with non-immersed lice after 6 h (100% vs. 76.6%, p = 0.0037), and 24 h (50.9% vs. 15.9%, p = 0.0003). Although water-immersed lice did not close their spiracles, water did not penetrate into the respiratory system. In contrast, immersion in colored dimeticone/cyclomethicone or colored ethanol resulted in penetration through the spiracles and spreading to the entire respiratory system within 30 min, leading to death in 100% of the lice.

Darker eggs of mosquitoes resist more to dry conditions: Melanin enhances serosal cuticle contribution in egg resistance to desiccation in Aedes, Anopheles and Culex vectors

Mosquito vectors lay their white eggs in the aquatic milieu. During early embryogenesis water passes freely through the transparent eggshell, which at this moment is composed of exochorion and endochorion. Within two hours the endochorion darkens via melanization but even so eggs shrink and perish if removed from moisture. However, during mid-embryogenesis, cells of the extraembryonic serosa secrete the serosal cuticle, localized right below the endochorion, becoming the third and innermost eggshell layer. Serosal cuticle formation greatly reduces water flow and allows egg survival outside the water. The degree of egg resistance to desiccation (ERD) at late embryogenesis varies among different species: Aedes aegypti, Anopheles aquasalis and Culex quinquefasciatus eggs can survive in a dry environment for ≥ 72, 24 and 5 hours, respectively. In some adult insects, darker-body individuals show greater resistance to desiccation than lighter ones. We asked if egg melanization enhances mosquito serosal cuticle-dependent ERD. Species with higher ERD at late embryogenesis exhibit more melanized eggshells. The melanization-ERD hypothesis was confirmed employing two Anopheles quadrimaculatus strains, the wild type and the mutant GORO, with a dark-brown and a golden eggshell, respectively. In all cases, serosal cuticle formation is fundamental for the establishment of an efficient ERD but egg viability outside the water is much higher in mosquitoes with darker eggshells than in those with lighter ones. The finding that pigmentation influences egg water balance is relevant to understand the evolutionary history of insect egg coloration. Since eggshell and adult cuticle pigmentation ensure insect survivorship in some cases, they should be considered regarding species fitness and novel approaches for vector or pest insects control.

Adaptive dynamics of cuticular hydrocarbons in Drosophila

Cuticular hydrocarbons (CHCs) are hydrophobic compounds deposited on the arthropod cuticle that are of functional significance with respect to stress tolerance, social interactions and mating dynamics. We characterized CHC profiles in natural populations of Drosophila melanogaster at five levels: across a latitudinal transect in the eastern United States, as a function of developmental temperature during culture, across seasonal time in replicate years, and as a function of rapid evolution in experimental mesocosms in the field. Furthermore, we also characterized spatial and temporal changes in allele frequencies for SNPs in genes that are associated with the production and chemical profile of CHCs. Our data demonstrate a striking degree of parallelism for clinal and seasonal variation in CHCs in this taxon; CHC profiles also demonstrate significant plasticity in response to rearing temperature, and the observed patterns of plasticity parallel the spatiotemporal patterns observed in nature. We find that these congruent shifts in CHC profiles across time and space are also mirrored by predictable shifts in allele frequencies at SNPs associated with CHC chain length. Finally, we observed rapid and predictable evolution of CHC profiles in experimental mesocosms in the field. Together, these data strongly suggest that CHC profiles respond rapidly and adaptively to environmental parameters that covary with latitude and season, and that this response reflects the process of local adaptation in natural populations of D. melanogaster.

SEM characterization of anatomical variation in chitin organization in insect and arthropod cuticles

The cuticles of insects and arthropods have some of the most diverse material properties observed in nature, so much so that it is difficult to imagine that all cutciles are primarily composed of the same two materials: a fibrous chitin network and a matrix composed of cuticle proteins. Various factors contribute to the mechanical and optical properties of an insect or arthropod cuticle including the thickness and composition. In this paper, we also identified another factor that may contribute to the optical, surface, and mechanical properties of a cuticle, i.e. the organization of chitin nanofibers and chitin fiber bundles. Self-assembled chitin nanofibers serve as the foundation for all higher order chitin structures in the cuticles of insects and other arthropods via interactions with structural cuticle proteins. Using a technique that enables the characterization of chitin organization in the cuticle of intact insects and arthropod exoskeletons, we demonstrate a structure/function correlation of chitin organization with larger scale anatomical structures. The chitin scaffolds in cuticles display an extraordinarily diverse set of morphologies that may reflect specific mechanical or physical properties. After removal of the proteinaceous and mineral matrix of a cuticle, we observe using SEM diverse nanoscale and micro scale organization of in-situ chitin in the wing, head, eye, leg, and dorsal and ventral thoracic regions of the periodical cicada Magicicada septendecim and in other insects and arthropods. The organization of chitin also appears to have a significant role in the organization of nanoscale surface structures. While microscale bristles and hairs have long been known to be chitin based materials formed as cellular extensions, we have found a nanostructured layer of chitin in the cuticle of the wing of the dog day annual cicada Tibicen tibicens, which may be the scaffold for the nanocone arrays found on the wing. We also use this process to examine the chitin organizations in the fruit fly, Drosophila melanogaster, and the Atlantic brown shrimp, Farfantepenaeus aztecus. Interestingly many of the homologous anatomical structures from diverse arthropods exhibit similar patterns of chitin organization suggesting that a common set of parameters, govern chitin organization.

Nano-enabled delivery of diverse payloads across complex biological barriers

Complex biological barriers are major obstacles for preventing and treating disease. Nanocarriers are designed to overcome such obstacles by enhancing drug delivery through physiochemical barriers and improving therapeutic indices. This review critically examines both biological barriers and nanocarrier payloads for a variety of drug delivery applications. A spectrum of nanocarriers is discussed that have been successfully developed for improving tissue penetration for preventing or treating a range of infectious, inflammatory, and degenerative diseases.

Mechanical properties of the cuticles of three cockroach species that differ in their wind-evoked escape behavior

The structural and material properties of insect cuticle remain largely unexplored, even though they comprise the majority (approximately 80%) of animals. Insect cuticle serves many functions, including protection against predatory attacks, which is especially beneficial to species failing to employ effective running escape responses. Despite recent advances in our understanding of insect escape behaviors and the biomechanics of insect cuticle, there are limited studies on the protective qualities of cuticle to extreme mechanical stresses and strains imposed by predatory attacks, and how these qualities vary between species employing different escape responses. Blattarians (cockroaches) provide an appropriate model system for such studies. Wind-evoked running escape responses are strong in Periplaneta americana, weak in Blaberus craniifer and absent in Gromphodorhina portentosa, putting the latter two species at greater risk of being struck by a predator. We hypothesized that the exoskeletons in these two larger species could provide more protection from predatory strikes relative to the exoskeleton of P. americana. We quantified the protective qualities of the exoskeletons by measuring the puncture resistance, tensile strength, strain energy storage, and peak strain in fresh samples of thoracic and abdominal cuticles from these three species. We found a continuum in puncture resistance, tensile strength, and strain energy storage between the three species, which were greatest in G. portentosa, moderate in B. craniifer, and smallest in P. americana. Histological measurements of total cuticle thickness followed this same pattern. However, peak strain followed a different trend between species. The comparisons in the material properties drawn between the cuticles of G. portentosa, B. craniifer, and P. americana demonstrate parallels between cuticular biomechanics and predator running escape responses.

Melanins: Skin Pigments and Much More—Types, Structural Models, Biological Functions, and Formation Routes

This review presents a general view of all types of melanin in all types of organisms. Melanin is frequently considered just an animal cutaneous pigment and is treated separately from similar fungal or bacterial pigments. Similarities concerning the phenol precursors and common patterns in the formation routes are discussed. All melanins are formed in a first enzymatically-controlled phase, generally a phenolase, and a second phase characterized by an uncontrolled polymerization of the oxidized intermediates. In that second phase, quinones derived from phenol oxidation play a crucial role. Concerning functions, all melanins show a common feature, a protective role, but they are not merely photoprotective pigments against UV sunlight. In pathogenic microorganisms, melanization becomes a virulence factor since melanin protects microbial cells from defense mechanisms in the infected host. In turn, some melanins are formed in tissues where sunlight radiation is not a potential threat. Then, their redox, metal chelating, or free radical scavenging properties are more important than light absorption capacity. These pigments sometimes behave as a double-edged sword, and inhibition of melanogenesis is desirable in different cells. Melanin biochemistry is an active field of research from dermatological, biomedical, cosmetical, and microbiological points of view, as well as fruit technology.

Superhydrophobic cuticle with a "pinning effect" in the larvae of the iris sawfly, Rhadinoceraea micans (Hymenoptera, Tenthredinidae)

The integument of some sawfly larvae can be easily damaged causing haemolymph bleeding (easy bleeding phenomenon). In the present study, we investigated intact cuticle, cuticle without wax coverage and cuticle replicas of sawfly larvae by using cryo-scanning electron microscopy and contact angle (CA) measurements. The easy bleeder Rhadinoceraea micans was compared to the non-easy bleeder Nematus pavidus (both Tenthredinidae), and the examination showed that the surface structures of R. micans were hierarchically arranged, whereas the cuticle surface of N. pavidus appeared much smoother. The intact cuticle proved to be superhydrophobic in R. micans (CAs: 156° dorsally, 120° ventrally), but not in N. pavidus (CAs: 67° dorsally, 47° ventrally). The wettability of R. micans increased significantly after the waxes had been peeled off. Replicas of the intact cuticle surface were hardly wettable in both species. It is suggested that wax crystals in combination with cuticle microsculptures are the most important features for rendering the integument of the easy bleeder species superhydrophobic. The wax-free tips of the cuticle microsculptures in R. micans are sites where haemolymph droplets can adhere. The integument surface of easy bleeders is assumed to be adapted to their particular defence strategy, simultaneously contributing to the maintenance and "reuse" of released haemolymph droplets on the superhydrophobic surface due to this "pinning effect".

Studies on the structure of the female reproductive system and egg-shell formation inAspiculuris tetrapteraSchulz, (Nematoda: Oxyuroidea)

The histological anatomy of the female reproductive system of an oxyuroid nematode,Aspiculuris tetraptera, Schulz, has been described.

The process of egg-shell formation in this animal has been followed in detail while the structural and chemical characteristics of the egg-shell have been studied by histochemical and other methods. It is shown that there are three layers: a lipoprotein layer, a ‘chitinous’ layer and the so-called vitelline (glycosidal) membrane. Evidence is presented for the exogenous origin of the lipoprotein layer: this being formed by the cells of the upper uterus which are shown to be secretory.

The question of quinone-tanning in the egg-shell ofA. tetrapteraand in other oxyuroids and ascarids is considered. It is shown that neither a polyphenol oxidase nor a high concentration of phenolic substances (apart from protein tyrosine) exists in this system. The significance of these and other observations is discussed in relation to the mechanism of tanning as elucidated in insects and trematodes.

I have to acknowledge with gratitude the support of many during these investigations. To Dr P. Tate for his encouragement and provision of facilities at the Molteno Institute; to Dr D. L. Lee, for much useful discussion and permission to refer to some of his unpublished electron micrographs of nematodes; to Professor J. D. Smyth, who kindly read through the manuscript; to the Cambridge Philosophical Society for a grant that made possible the translation of Fauré-Frémiet's classical study onAscaris;and to the Department of Technical Cooperation for financial assistance.

Photovoltaic Effects in Hornets Are Correlated with the Time of Day¶

This study deals with voltage values recorded off the cuticle of live specimens of the Oriental hornet Vespa orientalis (Hymenoptera, Vespidae). The relevant measurements were taken between the two tips of their bodies at various hours of the day and were made on a total of 90 worker hornets. Recorded voltage values varied within a range of 60-180 mV, with the lower values measured during the morning hours and the afternoon and the highest values during the noon hours. Measurements were made by direct contact of the electrodes with the hornet cuticle and did not prove lethal to the measured specimens. An additional 60 live hornets were measured in the same fashion but in the dark. The values recorded in the dark varied between 40 and 70 mV and displayed considerable fluctuations but were not found to be dependent on the time of measurement. The distribution of the voltage values in hornets measured at various hours in the daytime closely resembled that of the global radiations (in W/m2) on the same days the measurements were taken.

Some unusual structures inLocusta migratoria migratorioidesand their probable function as thermoreceptors

Adults of the African migratory locust,Locusta migratoria migratorioides(Reiche & Fairmaire), are provided with paired, segmentally arranged, specialized areas on the surface of the head, thorax and abdominal segments one to seven. Those on the head have been called theantennal crescentsand those on the thorax and abdomen thefenestrae. The cuticle of these special areas and the cellular layer associated with it are both unusual in structure and differ markedly from other parts of the body wall. Experiments designed to discover the function of the crescents and fenestrae indicate that they are much more sensitive to heat than is the surface in general, and that they probably serve as thermoreceptors. The observations and exeriments of earlier workers on the behaviour of locusts and grasshoppers when exposed to sunlight and other sources of heat are more clearly understandable on the assumption that these specialized areas function as thermorecept.

A study of the oviducal glands and ovisacs of Balanus balanoides (L.) together with comparative observations on the ovisacs of Balanus hameri (Ascanius) and the reproductive biology of the two species

A mainly microscopical study has been carried out on the oviducal glands and ovisacs of two hermaphroditic sessile barnacles, Balanus balanoides and Balanus hameri . In both species each gland secretes an ovisac, once a year, for a very restricted period before copulation. The morphology of the glands of B. balanoides has been worked out from serial sections and a Plasticine model. Three regions have been established within the glands; two are ectodermal in origin, namely the main chamber and exit canal, while the third, the proximal chamber, is mesodermal. The exit canal is always lined with cuticle, but the main chamber for most of the year is not. However, in both species main chamber cells begin to secrete the ovisacs several weeks before copulation. Ovisacs are undoubtedly cuticular structures. The cytology of B. balanoides main chamber cells during the sequence of events leading to the formation of ovisacs has been followed by means of transmission electron microscopy. The cells each develop a long apical cytoplasmic extension; from these extensions and the apical cell surfaces secretions pass out to form the ovisac wall. This wall has two zones, an outer electron-dense zone 14 pm thick and an inner flocculent zone 6 pm thick. When fully formed the ovisac is released from the main chamber cells to lie in the oviducal gland lumen, although the neck of the ovisac continues to be firmly attached to specialized anchor cells. The cytoplasmic extensions of the main chamber cells break away with the ovisac as it is released and eventually form the pores in the ovisac wall. Scanning electron microscopy was used to examine such unstretched sacs. In B. balanoides the main chamber cells then partially retrogress, shedding secretions and portions of cytoplasm into the gland lumen. It is proposed that these ‘formed bodies’, by their osmotic activity, draw water and low molecular mass solutes into the gland lumen from the haemolymph. The ‘formed bodies ’ swell and burst, thereby accumulating fluid in the lumen of the gland, which becomes highly swollen. It is this fluid that has the activating factor(s), thought to be the ammonium ion, needed to activate inseminated sperm. In this condition B.balanoides becomes a receptive female. In B. hameri , although there is some retrogression of the main chamber cells with secretion of ‘formed bodies’, there is much less accumulation of fluid and so the oviducal glands do not become so highly swollen. The copulatory act of B. hameri was observed closely and comparison was made with that of B. balanoides . In B. hameri a single male is involved and a single insemination is sufficient for egg laying to commence, while in B. balanoides more than one male may be involved and multiple inseminations are needed before egg laying begins. Oocytes (eggs) pass from the ovaries down the oviducts and into the elastic ovisacs lying in the oviducal glands. As the ovisacs distend with eggs they first expel the oviducal gland fluid into the mantle cavity and then they themselves are forced out into the mantle cavity. As the stretching continues the ovisac wall becomes very thin and the pores enlarge. Although B. balanoides sperm, which are 0.5 pm in diameter, can easily pass into the 0.7 to 1.6 pm diameter pores of an unstretched ovisac, those of B. hameri , which are also 0.5 pm in diameter, need the ovisac to stretch and the pores to enlarge from their original diameter of 0.2 pm before sperm can pass through and fertilize the eggs. Inseminated sperm, in both species, are deposited as gelled masses. In B. balanoides the expelled oviducal gland fluid activates such sperm, but inseminated sperm of B. hameri become active in seawater. At any one time, only those sperm on the outer surface of the masses are active, and so a staggered release takes place. This is essential when egg laying takes more than 30 min and the sperm of B. balanoides and B. hameri are active for only 5-6 min and 12-13 min respectively. The fully formed egg masses are finally freed from the anchor cells within the glands and moved to the bottom of the mantle cavity, where egg development takes place.

The cuticle of the cockroachPeriplaneta americana- V. The chemical resistance of the impregnating material of the cuticle, and the 'self-tanning' of its protein component

The developing cuticle ofPeriplanetashows some resistance to chemical attack even before the onset of the phenolic tanning which gives it its final hardness and colour. This early resistance is due to the impregnation of the cuticle with a lipoprotein complex. Histological and histochemical examination suggest that the combination of the sterol and protein moieties of the complex is dependent on the occurrence of some degree of aromatic bonding of the protein even before final tanning takes place. During this initial or primary aromatic bonding no marked colour is developed, and the active agent is not derived from a dihydroxyphenol, as it is in final tanning, but is a quinone formed by the oxidation insituof the tyrosine component of the protein moiety. No free dihydroxyphenol is involved, and the protein may be referred to as ‘self-tanning’. During the process of final hardening the protein of the impregnating complex undergoes further tanning. There is some evidence that the sterol also may be involved in this process, not merely through its association with the protein, but directly owing to its combination with the tanning agent.

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.

Synthesis of the major adult cuticle proteins of Drosophila melanogaster during hypoderm differentiation

Differentiating imaginal hypodermal cells of Drosophila melanogaster form adult cuticle during the second half of the pupal stage (about 40 to 93 hr postpupariation). A group of proteins with molecular weights of 23,000, 20,000, and 14,000 is identified as putative major wing cuticle proteins with the following biological properties: These proteins are abundant components of cuticle and are major synthetic products of cuticle-secreting hypodermal cells. They are leucine-rich and methionine-free and are the most prominent proteins of this type synthesized by wing hypoderm at 65 hr, during the period of procuticle formation. Electron microscopic autoradiography shows that leucine-rich, methionine-free proteins specifically localize to the apical cell surface and newly secreted cuticle of 65-hr wing cells. This strongly suggests the export of these proteins to the cuticle. Lastly, these proteins undergo a reduction in extractability just after eclosion, during the period of cuticle protein crosslinking (sclerotization). The synthesis of these major hypoderm proteins is temporally regulated in development. In wing cells, the 14-kDa proteins are synthesized first, from 53 to 78 hr, and the 20- and 23-kDa proteins are synthesized from 63 to 93 hr. The pattern of synthesis for these proteins is similar in abdominal cells but delayed by 6 to 10 hr. Two-dimensional gel electrophoresis shows that each of the 23-, 20-, and 14-kDa size classes contains at least two component polypeptides. Patterns of protein synthesis in cells of the imaginal hypodermis are regulated in a precise temporal sequence during the production of adult cuticle. Their study yields a useful system for the analysis of molecular events in gene control and cell differentiation.