The salivary gland and salivary enzymes of the giant waterbugs (Heteroptera; Belostomatidae)

The Predatory Stink Bug Arma custos (Hemiptera: Pentatomidae) Produces a Complex Proteinaceous Venom to Overcome Caterpillar Prey

Predatory stink bugs capture prey by injecting salivary venom from their venom glands using specialized stylets. Understanding venom function has been impeded by a scarcity of knowledge of their venom composition. We therefore examined the proteinaceous components of the salivary venom of the predatory stink bug Arma custos (Fabricius, 1794) (Hemiptera: Pentatomidae). We used gland extracts and venoms from fifth-instar nymphs or adult females to perform shotgun proteomics combined with venom gland transcriptomics. We found that the venom of A. custos comprised a complex suite of over a hundred individual proteins, including oxidoreductases, transferases, hydrolases, ligases, protease inhibitors, and recognition, transport and binding proteins. Besides the uncharacterized proteins, hydrolases such as venom serine proteases, cathepsins, phospholipase A₂, phosphatases, nucleases, alpha-amylases, and chitinases constitute the most abundant protein families. However, salivary proteins shared by and unique to other predatory heteropterans were not detected in the A. custos venom. Injection of the proteinaceous (>3 kDa) venom fraction of A. custos gland extracts or venom into its prey, the larvae of the oriental armyworm Mythimna separata (Walker, 1865), revealed insecticidal activity against lepidopterans. Our data expand the knowledge of heteropteran salivary proteins and suggest predatory asopine bugs as a novel source for bioinsecticides.

You are what you eat-ecological niche and microhabitat influence venom activity and composition in aquatic bugs

True water bugs (Nepomorpha) are mostly predacious insects that live in aquatic habitats. They use their piercing-sucking mouthparts to inject venomous saliva that facilitates the capture and extra-oral digestion of prey animals, but their venom can also be deployed for defence. In Central Europe, nepomorph species representing different families coexist in the same habitat. However, their feeding ecology, including venom composition and deployment, has not been investigated in detail. We used an integrated proteotranscriptomic and bioactivity-based approach to test whether venom composition and activity differ between four water bug species sharing the same habitat but occupying different ecological niches. We found considerable species-dependent differences in the composition of digestive enzymes and venom components that probably evolved as adaptations to particular food sources, foraging strategies and/or microhabitats. The venom of Corixa punctata differed substantially from that of the three strictly predatory species (Ilyocoris cimicoides, Notonecta glauca and Nepa cinerea), and the abundance of herbivory-associated proteins confirms a mostly plant-based diet. Our findings reveal independent adaptations of the digestive and defensive enzyme repertoires accompanied by the evolution of distinct feeding strategies in aquatic bugs.

Proteotranscriptomic Analysis and Toxicity Assay Suggest the Functional Distinction between Venom Gland Chambers in Twin-Spotted Assassin Bug, Platymeris biguttatus

Assassin bugs use their salivary venoms for various purposes, including defense, prey paralyzation, and extra-oral digestion, but the mechanisms underlying the functional complexity of the venom remain largely unclear. Since venom glands are composed of several chambers, it is suggested that individual chambers may be specialized to produce chemically distinct venoms to exert different functions. The current study assesses this hypothesis by performing toxicity assays and transcriptomic and proteomic analysis on components from three major venom gland chambers including the anterior main gland (AMG), the posterior main gland (PMG), and the accessory gland (AG) of the assassin bug Platymeris biguttatus. Proteotranscriptomic analysis reveals that AMG and PMG extracts are rich in hemolytic proteins and serine proteases, respectively, whereas transferrin and apolipophorin are dominant in the AG. Toxicity assays reveal that secretions from different gland chambers have distinct effects on the prey, with that from AG compromising prey mobility, that from PMG causing prey death and liquifying the corpse, and that from AMG showing no significant physiological effects. Our study reveals a functional cooperation among venom gland chambers of assassin bugs and provides new insights into physiological adaptations to venom-based predation and defense in venomous predatory bugs.

"Fearing the enemy": Growth and stress biomarker responses of sexually reversed Oreochromis niloticus in the presence of aquatic predatory insects

Fishes can change their physiological responses when threatened by the presence of predators. Such physiological plasticity, however, usually implies costs that may impede organismal development and reproduction and reduce the ability to cope with other biotic and abiotic stresses. Here, we evaluated the growth and stress biomarker responses in sexually reversed Nile tilapia, Oreochromis niloticus, fingerlings indirectly threatened by the presence of the aquatic insect predator Belostoma anurum (Hemiptera: Belostomatidae). We also evaluated whether the presence of B. anurum would affect growth in fingerlings that received food containing the masculinizing hormone 17 α-methyltestosterone. The antioxidant responses were evaluated by measuring the activity of enzymes (e.g., superoxide dismutase, catalase, and glutathione-S-transferase). Oxidative stress biomarkers (e.g., malondialdehyde and nitric oxide) and blood glucose and lactate responses were also evaluated. Our results revealed that predator exposure did not affect growth in O. niloticus fingerlings reared in the presence or absence of the masculinizing hormone. However, sexually reversed tilapia fingerlings significantly increased not only the glucose and lactate blood levels, but also exhibited increased activities of superoxide dismutase and glutathione-S-transferases enzymes when threatened by the presence of B. anurum nymphs. Collectively, our findings indicate that despite not exhibiting reduced growth performance, sexually reversed tilapia fingerlings were physiologically stressed by the presence of the predator, which may reduce their ability to face environmental and abiotic stresses.

Extraoral digestion: outsourcing the role of the hemipteran midgut

Extraoral digestion allows for breakdown of dietary components before they reach the midgut for final enzymatic degradation and absorption. In the Hemiptera, this is achieved by the secretion of enzyme-rich fluids from the salivary gland, with the combination of protein and mRNA from these tissues termed the sialome. Separate channels within the hemipteran stylets allow for secretion of saliva and ingestion of predigested material in a non-reflux mechanism. Both feeding mode and diet type influence the composition of the hemipteran sialome, as illustrated by 1) differences in protease abundance between hematophagous and predatory heteropteran sialomes, 2) diet specific aminopeptidase-N genes among aphid biotypes, and 3) adaptation-induced sialome variation in related cicada populations. Despite challenges associated with incomplete genome annotation, -omics analysis of the sialomes of diverse hemipteran species will enhance understanding of both sialome function and the evolution of extraoral digestion within the order.

Context-dependent venom deployment and protein composition in two assassin bugs

The Heteroptera are a diverse suborder of phytophagous, hematophagous, and zoophagous insects. The shift to zoophagy can be traced back to the transformation of salivary glands into venom glands, but the venom is used not only to kill and digest invertebrate prey but also as a defense strategy, mainly against vertebrates. In this study, we used an integrated transcriptomics and proteomics approach to compare the composition of venoms from the anterior main gland (AMG) and posterior main gland (PMG) of the reduviid bugs Platymeris biguttatus L. and Psytalla horrida Stål. In both species, the AMG and PMG secreted distinct protein mixtures with few interspecific differences. PMG venom consisted mostly of S1 proteases, redulysins, Ptu1-like peptides, and uncharacterized proteins, whereas AMG venom contained hemolysins and cystatins. There was a remarkable difference in biological activity between the AMG and PMG venoms, with only PMG venom conferring digestive, neurotoxic, hemolytic, antibacterial, and cytotoxic effects. Proteomic analysis of venom samples revealed the context-dependent use of AMG and PMG venom. Although both species secreted PMG venom alone to overwhelm their prey and facilitate digestion, the deployment of defensive venom was species-dependent. P. biguttatus almost exclusively used PMG venom for defense, whereas P. horrida secreted PMG venom in response to mild harassment but AMG venom in response to more intense harassment. This intriguing context-dependent use of defensive venom indicates that future research should focus on species-dependent differences in venom composition and defense strategies among predatory Heteroptera.

Life History Traits and Predatory Performance of Belostoma anurum (Hemiptera: Belostomatidae), a Biological Control Agent of Disease Vector Mosquitoes

Understanding the life cycle and dietary requirements of laboratory-reared insects is critical for optimizing resources (including time) and can provide more reliable ecological basis for using such biological control agents in realistic programs. Here, we evaluated the complete development and the predatory abilities of Belostoma anurum (Herrich-Schäffer, 1848) (Hemiptera: Belostomatidae), an aquatic predator widely distributed in Neotropical region, when reared at different diets. We firstly investigated the predatory performance of B. anurum nymphs upon mosquito larvae (i.e., larvae of Aedes aegypti (Linnaeus, 1758) or Culex sp. (Diptera: Culicidae)) and, second, whether the immature diets (i.e., arthropod-based diet (mosquito larvae and adults of Notonectidae) or vertebrate (fish larvae)-based diet) affect the predatory behavior of B. anurum adults. The B. anurum egg-to-adult developmental time was 85.1 days in an arthropod-based diet. However, when a fish-based diet was offered after nymphs reached 3rd instar, we recorded up to 50% reductions on the B. anurum developmental time. Interestingly, B. anurum adults could live more than 1 year under laboratory conditions, independently of the immature diet regime. Furthermore, the fish diet-experienced B. anurum adults spent less time feeding on fish larvae when compared with adults that never experienced this type of diet. Predatory results revealed that 2nd instar B. anurum were more efficient to catch and consume larvae of A. aegypti than of Culex sp. Collectively, our findings show that B. anurum is long-lived aquatic predators, and demonstrate the impacts of dietary regime on the life history traits and predatory performance of these insects.

Giant fish-killing water bug reveals ancient and dynamic venom evolution in Heteroptera

True Bugs (Insecta: Heteroptera) produce venom or saliva with diverse bioactivities depending on their feeding strategies. However, little is known about the molecular evolution of the venom toxins underlying these biological activities. We examined venom of the giant fish-killing water bug Lethocerus distinctifemur (Insecta: Belostomatidae) using infrared spectroscopy, transcriptomics, and proteomics. We report 132 venom proteins including putative enzymes, cytolytic toxins, and antimicrobial peptides. Over 73% (96 proteins) showed homology to venom proteins from assassin bugs (Reduviidae), including 21% (28 proteins from seven families) not known from other sources. These data suggest that numerous protein families were recruited into venom and diversified rapidly following the switch from phytophagy to predation by ancestral heteropterans, and then were retained over > 200 my of evolution. In contrast, trophic switches to blood-feeding (e.g. in Triatominae and Cimicidae) or reversions to plant-feeding (e.g., in Pentatomomorpha) were accompanied by rapid changes in the composition of venom/saliva, including the loss of many protein families.

X-ray computed tomography and its potential in ecological research: A review of studies and optimization of specimen preparation

Imaging techniques are a cornerstone of contemporary biology. Over the last decades, advances in microscale imaging techniques have allowed fascinating new insights into cell and tissue morphology and internal anatomy of organisms across kingdoms. However, most studies so far provided snapshots of given reference taxa, describing organs and tissues under "idealized" conditions. Surprisingly, there is an almost complete lack of studies investigating how an organism's internal morphology changes in response to environmental drivers. Consequently, ecology as a scientific discipline has so far almost neglected the possibilities arising from modern microscale imaging techniques. Here, we provide an overview of recent developments of X-ray computed tomography as an affordable, simple method of high spatial resolution, allowing insights into three-dimensional anatomy both in vivo and ex vivo. We review ecological studies using this technique to investigate the three-dimensional internal structure of organisms. In addition, we provide practical comparisons between different preparation techniques for maximum contrast and tissue differentiation. In particular, we consider the novel modality of phase contrast by self-interference of the X-ray wave behind an object (i.e., phase contrast by free space propagation). Using the cricket Acheta domesticus (L.) as model organism, we found that the combination of FAE fixative and iodine staining provided the best results across different tissues. The drying technique also affected contrast and prevented artifacts in specific cases. Overall, we found that for the interests of ecological studies, X-ray computed tomography is useful when the tissue or structure of interest has sufficient contrast that allows for an automatic or semiautomatic segmentation. In particular, we show that reconstruction schemes which exploit phase contrast can yield enhanced image quality. Combined with suitable specimen preparation and automated analysis, X-ray CT can therefore become a promising quantitative 3D imaging technique to study organisms' responses to environmental drivers, in both ecology and evolution.

Harvesting Venom Toxins from Assassin Bugs and Other Heteropteran Insects

Heteropteran insects such as assassin bugs (Reduviidae) and giant water bugs (Belostomatidae) descended from a common predaceous and venomous ancestor, and the majority of extant heteropterans retain this trophic strategy. Some heteropterans have transitioned to feeding on vertebrate blood (such as the kissing bugs, Triatominae; and bed bugs, Cimicidae) while others have reverted to feeding on plants (most Pentatomomorpha). However, with the exception of saliva used by kissing bugs to facilitate blood-feeding, little is known about heteropteran venoms compared to the venoms of spiders, scorpions and snakes. One obstacle to the characterization of heteropteran venom toxins is the structure and function of the venom/labial glands, which are both morphologically complex and perform multiple biological roles (defense, prey capture, and extra-oral digestion). In this article, we describe three methods we have successfully used to collect heteropteran venoms. First, we present electrostimulation as a convenient way to collect venom that is often lethal when injected into prey animals, and which obviates contamination by glandular tissue. Second, we show that gentle harassment of animals is sufficient to produce venom extrusion from the proboscis and/or venom spitting in some groups of heteropterans. Third, we describe methods to harvest venom toxins by dissection of anaesthetized animals to obtain the venom glands. This method is complementary to other methods, as it may allow harvesting of toxins from taxa in which electrostimulation and harassment are ineffective. These protocols will enable researchers to harvest toxins from heteropteran insects for structure-function characterization and possible applications in medicine and agriculture.

The assassin bug Pristhesancus plagipennis produces two distinct venoms in separate gland lumens

The assassin bug venom system plays diverse roles in prey capture, defence and extra-oral digestion, but it is poorly characterised, partly due to its anatomical complexity. Here we demonstrate that this complexity results from numerous adaptations that enable assassin bugs to modulate the composition of their venom in a context-dependent manner. Gland reconstructions from multimodal imaging reveal three distinct venom gland lumens: the anterior main gland (AMG); posterior main gland (PMG); and accessory gland (AG). Transcriptomic and proteomic experiments demonstrate that the AMG and PMG produce and accumulate distinct sets of venom proteins and peptides. PMG venom, which can be elicited by electrostimulation, potently paralyses and kills prey insects. In contrast, AMG venom elicited by harassment does not paralyse prey insects, suggesting a defensive role. Our data suggest that assassin bugs produce offensive and defensive venoms in anatomically distinct glands, an evolutionary adaptation that, to our knowledge, has not been described for any other venomous animal.

Venom can be used both offensively for prey capture and defensively to deter predators. Here, Walker and colleagues demonstrate that the assassin bug Pristhesancus plagipennis has two distinct venom glands that produce venoms with distinct compositions that can be elicited by different stimuli.

Venoms of Heteropteran Insects: A Treasure Trove of Diverse Pharmacological Toolkits

The piercing-sucking mouthparts of the true bugs (Insecta: Hemiptera: Heteroptera) have allowed diversification from a plant-feeding ancestor into a wide range of trophic strategies that include predation and blood-feeding. Crucial to the success of each of these strategies is the injection of venom. Here we review the current state of knowledge with regard to heteropteran venoms. Predaceous species produce venoms that induce rapid paralysis and liquefaction. These venoms are powerfully insecticidal, and may cause paralysis or death when injected into vertebrates. Disulfide-rich peptides, bioactive phospholipids, small molecules such as N,N-dimethylaniline and 1,2,5-trithiepane, and toxic enzymes such as phospholipase A2, have been reported in predatory venoms. However, the detailed composition and molecular targets of predatory venoms are largely unknown. In contrast, recent research into blood-feeding heteropterans has revealed the structure and function of many protein and non-protein components that facilitate acquisition of blood meals. Blood-feeding venoms lack paralytic or liquefying activity but instead are cocktails of pharmacological modulators that disable the host haemostatic systems simultaneously at multiple points. The multiple ways venom is used by heteropterans suggests that further study will reveal heteropteran venom components with a wide range of bioactivities that may be recruited for use as bioinsecticides, human therapeutics, and pharmacological tools.

Enzyme Activity, Cold Hardiness, and Supercooling Point in Developmental Stages of Acrosternum arabicum (Hemiptera: Pentatomidae)

Several species of pentatomid bugs feed on pistachio fruits in Iran. Acrosternum arabicum Wagner (Hemiptera: Pentatomidae) is one of the most important pests of pistachio in Rafsanjan, Iran. This study was carried out to investigate the carbohydrase activities, supercooling points, and cold hardiness profiles of different developmental stages of A. arabicum under laboratory conditions. The midgut amylolytic of A. arabicum showed an optimal pH at 7.0. The highest amylolytic activity was found in the female adults (35.41 ± 0.90 nmol/min/gut). The mean amylolytic activity measured in first instar nymph was 6.75 ± 0.54 nmol/min/gut. Midgut α- and β-glucosidase showed an optimal activity at pH 5 and 7, respectively. These activities increased from first (83 ± 5 and 54 ± 5 nmol/min, respectively) to fifth (881 ± 17 and 237 ± 14 nmol/min, respectively) instar nymphs. The enzyme activities increased in the adults. Midgut α- and β-galactosidase showed an optimal activity at pH 5. α- and β-galactosidase activities were low in the first instar nymphs (73 ± 5 and 21 ± 3 nmol/min, respectively). The level of α- and β-galactosidase activities in the female adults (533 ± 18 and 246 ± 6 nmol/min, respectively) was higher than the nymphs. The lowest super cooling points (-19 and -18.2 °C, respectively) and the highest cold hardiness (22 and 18% following 24 h exposure at - 20 °C, respectively) were recorded for the eggs and adult females.

Stink bug predator kills prey with salivary non-proteinaceous compounds

Podisus nigrispinus Dallas (Hemiptera: Pentatomidae) is a predator insect with potential applications in biological control because both nymphs and adults have been shown to prey on other insect pests by injection of toxic salivary gland contents. This study identified non-proteinaceous compounds with insecticidal activity from the saliva of P. nigrispinus in Anticarsia gemmatalis. In particular, the ether extract from P. nigrispinus saliva led to mortality in A. gemmatalis larvae, with a LC50 = 2.04 μL and LC90 = 3.27 μL. N,N-dimethylaniline and 1,2,5-trithiepane fractions were identified as non-proteinaceous extract components. N,N-dimethylaniline had a LC50 = 136.1 nL and LC90 = 413.8 nL, suggesting that it could be responsible for toxicity in P. nigrispinus saliva.

Morphology and ultrastructure of the salivary glands of the spittlebug Lepyronia coleopterata (L.) (Hemiptera: Aphrophoridae)

We investigated the salivary glands in Lepyronia coleopterata (L.), and found that the salivary glands are paired structures and consist of principal and accessory glands. Each principal gland contains an anterior lobe and a posterior lobe. Three types of acini (I, II, III) are observed in the anterior lobe, whereas the posterior lobe contains only one type of acini (IV). Rhabdus emerges from the middle portion of the acini III and IV. The oval-shaped accessory gland connects with the principal gland via a long duct. The long duct consists of a slightly coiled basal segment and a highly convoluted distal segment, with the terminal end of the latter constricted and connected with the accessory gland. A slightly convoluted transparent tube connects with the accessory gland at the former's distal end. The accessory gland, accessory salivary duct and the accessory salivary tube are observed for the first time in spittlebugs. Ultrastructurally, each type of acinus is made up of one type of secretory cells, but the rhabdus comprises two types of cells. Secretory granules in different type of cells are different in size, shape and electron density, which indicate either different materials are synthesized or these materials undergo a process of maturation. The rhabdus is empty in structure and contains several channels, with the lumen filled with abundant fine granular materials. Fine dark granules existed in the periphery of some secretory granules are probably virus particles. Microorganisms are observed in the cells of the acini I, III and rhabdus.

Salivary digestive enzymes of the wheat bug, Eurygaster integriceps (Insecta: Hemiptera: Scutelleridae)

The digestive enzymes from salivary gland complexes (SGC) of Eurygaster integriceps, and their response to starvation and feeding were studied. Moreover, digestive amylases were partially purified and characterized by ammonium sulfate precipitation and gel filtration chromatography. The SGC are composed of two sections, the principal glands and accessory glands. The principal glands are further divided into the anterior lobes and posterior lobes. The SGC main enzyme was α-amylase, which hydrolyzed starch better than glycogen. The other carbohydrases were also present in the SGC complexes. Enzymatic activities toward mannose (α/β-mannosidases) were little in comparison to activities against glucose (α/β-glucosidases) and galactose (α/β-galactosidases), the latter being the greatest. Acid phosphatase showed higher activity than alkaline phosphatase. There was no measurable activity for lipase and aminopeptidase. Proteolytic activity was detected against general and specific protease substrates. Activities of all enzymes were increased in response to feeding in comparison to starved insects, revealing their induction and secretion in response to feeding pulse. The SGC amylases eluted in four major peaks and post-electrophoretic detection of the α-amylases demonstrated the existence of at least five isoamylases in the SGC. The physiological implication of these findings in pre-oral digestion of E. integriceps is discussed.

Regulation of mycolactone, the Mycobacterium ulcerans toxin, depends on nutrient source

BACKGROUND

Mycobacterium ulcerans, a slow-growing environmental bacterium, is the etiologic agent of Buruli ulcer, a necrotic skin disease. Skin lesions are caused by mycolactone, the main virulence factor of M. ulcerans, with dermonecrotic (destruction of the skin and soft tissues) and immunosuppressive activities. This toxin is secreted in vesicles that enhance its biological activities. Nowadays, it is well established that the main reservoir of the bacilli is localized in the aquatic environment where the bacillus may be able to colonize different niches. Here we report that plant polysaccharides stimulate M. ulcerans growth and are implicated in toxin synthesis regulation.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, by selecting various algal components, we have identified plant-specific carbohydrates, particularly glucose polymers, capable of stimulating M. ulcerans growth in vitro. Furthermore, we underscored for the first time culture conditions under which the polyketide toxin mycolactone, the sole virulence factor of M. ulcerans identified to date, is down-regulated. Using a quantitative proteomic approach and analyzing transcript levels by RT-qPCR, we demonstrated that its regulation is not at the transcriptional or translational levels but must involve another type of regulation. M. ulcerans produces membrane vesicles, as other mycobacterial species, in which are the mycolactone is concentrated. By transmission electron microscopy, we observed that the production of vesicles is independent from the toxin production. Concomitant with this observed decrease in mycolactone production, the production of mycobacterial siderophores known as mycobactins was enhanced.

CONCLUSIONS/SIGNIFICANCE

This work is the first step in the identification of the mechanisms involved in mycolactone regulation and paves the way for the discovery of putative new drug targets in the future.

Mycobacterium ulcerans causes minimal pathogenesis and colonization in medaka (Oryzias latipes): an experimental fish model of disease transmission

Mycobacterium ulcerans causes Buruli ulcer in humans, a progressive ulcerative epidermal lesion due to the mycolactone toxin produced by the bacterium. Molecular analysis of M. ulcerans reveals it is closely related to Mycobacterium marinum, a pathogen of both fish and man. Molecular evidence from diagnostic PCR assays for the insertion sequence IS2404 suggests an association of M. ulcerans with fish. However, fish infections by M. ulcerans have not been well documented and IS2404 has been found in other mycobacteria. We have thus, employed two experimental approaches to test for M. ulcerans in fish. We show here for the first time that M. ulcerans with or without the toxin does not mount acute or chronic infections in Japanese Medaka "Oryzias latipes" even at high doses. Moreover, M. ulcerans-infected medaka do not exhibit any visible signs of infection nor disease and the bacteria do not appear to replicate over time. In contrast, similar high doses of the wild-type M. marinum or a mycolactone-producing M. marinum "DL" strain are able to mount an acute disease with mortality in medaka. Although these results would suggest that M. ulcerans does not mount infections in fish we have evidence that CLC macrophages from goldfish are susceptible to mycolactones.

Role of proteases in extra-oral digestion of a predatory bug, Andrallus spinidens

Roles of salivary proteases in the extra-oral digestion of the predatory bug, Andrallus spinidens Fabricius (Hemiptera: Pentatomidae) were studied by using 2% azocasein as a general substrate and specific protease substrates, as well as synthetic and endogenous inhibitors. It was found that salivary glands of A. spinidens have two anterior, two lateral, and two posterior lobes. Azocasein was used to measure the activity of general proteases in the salivary glands using different buffer solutions. The enzyme had the highest activity at pH 8. General protease activity was highest at 40 °C and was stable for 6-16 hours. The use of specific substrates showed that trypsin-like, chymotrypsin-like, aminopeptidase, and carboxypeptidase are the active proteases present in salivary glands, by the maximum activity of trypsin-like protease in addition to their optimal pH between 8-9. Ca(2+) and Mg(2+) increased proteolytic activity about 216%, while other ions decreased it. Specific inhibitors including SBTI, PMSF, TLCK, and TPCK significantly decreased enzyme activity, as well as the specific inhibitors of methalloproteases including phenanthroline, EGTA, and TTHA. Extracted endogenous trypsin inhibitors extracted from potential prey, Chilo suppressalis, Naranga aenescens, Pieris brassicae, Hyphantria cunea, and Ephestia kuhniella, had different effects on trypsin-like protease activity of A. spinidens salivary glands. With the exception of C. suppressalis, the endogenous inhibitors significantly decreased enzyme activity in A. spinidens.

Density-Dependent Effects of Amphibian Prey on the Growth and Survival of an Endangered Giant Water Bug

Amphibian predator-insect prey relationships are common in terrestrial habitats, but amphibian larvae are preyed upon by a variety of aquatic hemipterans in aquatic habitats. This paper suggests that the survival of the nymphs of the endangered aquatic hemipteran Kirkaldyia (=Lethocerus) deyrolli (Belostomatidae: Heteroptera) is directly and indirectly affected by the abundance of their amphibian larval prey (tadpoles). Young nymphs of K. deyrolli mainly feed on tadpoles, regardless of differences in prey availability. Nymphs provided with tadpoles grow faster than nymphs provided with invertebrate prey. Therefore, tadpole consumption seems to be required to allow the nymphs to complete their larval development. In addition, the survival of K. deyrolli nymphs was greater during the period of highest tadpole density (June) than during a period of low tadpole density (July). Higher tadpole density moderates predation pressure from the water scorpion Laccotrephes japonensis (Nepidae: Heteroptera) on K. deyrolli nymphs; i.e., it has a density-mediated indirect effect. These results suggest that an abundance of tadpoles in June provides food for K. deyrolli nymphs (a direct bottom-up effect) and moderates the predation pressure from L. japonensis (an indirect bottom-up effect). An abundance of amphibian prey is indispensable for the conservation of this endangered giant water bug species.

Paralytic activity of lysophosphatidylcholine from saliva of the waterbug Belostoma anurum

Lysophosphatidylcholine (LPC) is a major bioactive lipid that is enzymatically generated by phospholipase A2 (PLA2). Previously, we showed that LPC is present in the saliva of the blood-sucking hemipteran Rhodnius prolixus and modulates cell-signaling pathways involved in vascular biology, which aids blood feeding. Here, we show that the saliva of the predator insect Belostoma anurum contains a large number of lipids with LPC accounting for 25% of the total phospholipids. A PLA2 enzyme likely to be involved in LPC generation was characterized. The activity of this enzyme is 5-fold higher in Belostoma saliva than in other studied hemipterans, suggesting a close association with the predator feeding habits of this insect. Belostoma employs extra-oral digestion, which allows for ingestion of larger prey than itself, including small vertebrates such as amphibians and fish. Therefore, prey immobilization during digestion is essential, and we show here that Belostoma saliva and B. anurum saliva purified LPC have paralytic activity in zebrafish. This is the first evidence that lysophospholipids might play an important role in prey immobilization, in addition to contributing to blood feeding, and might have been an evolutionary acquisition that occurred long before the appearance of hematophagy in this animal group.

A salivary serine protease of the haematophagous reduviid Panstrongylus megistus: sequence characterization, expression pattern and characterization of proteolytic activity

A cDNA encoding a trypsin-like protease from the salivary glands of the haematophagous reduviid Panstrongylus megistus was cloned and sequenced. The deduced protein sequence showed similarities to serine proteases of other hemipterans but with substitutions in the catalytic triad and the substrate binding site. The expression of the gene increased more than sixfold after feeding. Saliva showed the highest proteolytic activity at neutral to slightly basic pH. Substrate and inhibitor profiles and zymography indicated the presence of a trypsin-like protease with preference for Arg and Lys at P1. Using chromatography, a fibrinolytic enzyme was purified whose sequence was identified by tandem mass spectrometry as that encoded by the cDNA.

Bites caused by giant water bugs belonging to Belostomatidae family (Hemiptera, Heteroptera) in humans: a report of seven cases

We report 7 cases of patients bitten by giant water bugs, large predatory insects belonging to the Belostomatidae family (Hemiptera, Heteroptera). These insects have toxic saliva capable of provoking intense pain and paralysis in vertebrates. Victims experienced intense, excruciating pain and 1 manifested hypoesthesia in the forearm. Bites by Belostomatidae are often reported by clinicians working in areas where these insects live, but there are no detailed case reports in the medical literature. There are no specific treatment modalities known to be effective, making prevention an important strategy.

Ontogenetic dietary shift in the larvae of Cybister japonicus (Coleoptera: Dytiscidae) in Japanese rice fields

A number of fragmentary reports suggest that the endangered diving beetle Cybister japonicus larvae feed on tadpoles, fish, and aquatic insects. However, no quantitative study on the feeding habits of C. japonicus larvae has been reported. In this study, field observations and rearing experiments were carried out to show the feeding ecology of C. japonicus larvae. Unlike previous commentaries, the first- and second-instar larvae of C. japonicus preyed on insects, mainly Odonata nymphs and Notonecta triguttata, irrespective of prey availability, but did not eat vertebrates such as tadpoles and fish in the field. On the contrary, the third-instar larvae fed on both insects and vertebrates. Rearing experiments showed that the number of Odonata nymphs consumed was significantly more than the number of tadpoles consumed by the first and second instars but third-instar larvae ate both the Odonata nymphs and tadpoles in the tadpole-Odonata nymph mixture experiment. The total body lengths of C. japonicus new adults in the Odonata nymph and tadpole-Odonata nymph mixture treatments were statistically equal. These results suggested that the first- and second-instar larvae of C. japonicus prey mainly on insects and do not eat vertebrate animals (insectivore), whereas the third-instar larvae fed on both insects and vertebrates (generalist).

Ultrastructure of the salivary glands in Cimex hemipterus (Hemiptera: Cimicidae)

Cimex hemipterus (Fabricius) is a hematophagous insect that can be an experimental host of Trypanosoma cruzi and may play a role as vector of Chagas' disease. This work analyzed the structure of the salivary glands of C. hemipterus. The secretory portion of main salivary glands has a single oval lobe that is translucent and is formed from a simple columnar epithelium lined by muscle cells. The gland cells are high, with one or two spherical nuclei, nucleolus, and some condensed chromatin. The cell cytoplasm has a well-developed rough endoplasmic reticulum, electron lucent vesicles, lysosomes, and glycogen deposits. The apical plasma membrane has microvilli, zonula adherens, and desmosomes, whereas the basal plasma membrane has some infoldings associated with mitochondria. The duct of the main salivary glands has flattened cells. The secretory portion of the accessory salivary glands is a single vesicular lobe that is translucent and is formed from a single layer of cells that varies from flattened to cubical onto muscle cells. The cytoplasm contains a well-developed smooth endoplasmic reticulum, vacuoles of different sizes containing secretions, electron lucent, and abundant mitochondria. The baso-lateral plasma membrane of adjacent cells shows septate junctions. The duct is formed from a flattened epithelium like the duct of the principal salivary gland. The secretory cells of the main salivary glands are related to protein synthesis and transport of ions. However, the secretory cells of the accessory salivary glands are related mainly to transport of ions and water from the hemolymph to glandular lumen.

Persistent association of Mycobacterium ulcerans with West African predaceous insects of the family belostomatidae

A number of studies have suggested that Mycobacterium ulcerans, the etiological agent of Buruli ulcer, may be transmitted to humans by insect bites. M. ulcerans has been isolated from a predaceous aquatic insect, and PCR detection of M. ulcerans DNA in aquatic environments suggests that the organism is widely distributed within many invertebrate taxa and functional feeding groups. Thus, M. ulcerans may be concentrated through different trophic links. However, the specific environmental niche of M. ulcerans and route of transmission to humans remain a mystery. In this study, a biologically relevant infection model in which M. ulcerans-infected mosquito larvae were fed to a species of predaceous hemiptera (African Belostomatidae) was used to demonstrate the persistent colonization of M. ulcerans and subsequent transmission of bacteria to naïve prey. The association of M. ulcerans with specific anatomical compartments showed that M. ulcerans accumulates preferentially on the exoskeleton. In contrast, few organisms were found in dissected guts or salivary glands. No difference was found between the ability of wild-type M. ulcerans and an M. ulcerans isogenic mycolactone-negative mutant to colonize belostomatids. These data show that African belostomatids can successfully be colonized by M. ulcerans and support the trophic transfer of M. ulcerans within the environment.