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PubMed2006

Individual and joint actions of selenate and methylmercury on the development and survival of insect detritivore Megaselia scalaris (Diptera: Phoridae).

Despite the important roles played by insects in most ecosystems, surprisingly little is known about how anthropogenic pollutants or their mixtures interact to affect insect populations. The independent and joint actions of selenate and methylmercury on a ubiquitous insect detritivore, Megaselia scalaris (Loew), were determined in this study. Ovipositing females did not distinguish between untreated food sources and those contaminated with toxic concentrations of selenate, methylmercury, or both chemicals in combination. Even at the highest concentrations of pollutants, no negative effects were observed for the egg stage. However, larval survival was significantly decreased and development significantly prolonged by selenate and methylmercury individually at low or intermediate ecologically relevant treatment levels. Potentiation was strongly evident because mixtures containing concentrations as little as only 1% of the respective individual median lethal tolerances (LC(50)s) caused significantly more mortality and delayed larval development than would be expected from the responses selenate and methylmercury elicit individually. However, survival and pupal development was not affected at any rate tested. Female fecundity was significantly decreased by methylmercury but not by selenate or mixture treatments. The relative toxicity to M. scalaris of each of the individual and joint treatments was selenate (LC(50) = 260 microg/g) < methylmercury (LC(50) = 22 microg/g) < the mixture at approximately 5% of the LC(50) concentration of each of the components (12 microg/g selenate plus 1.0 microg/g methylmercury). The increased mortality and delayed larval development within sites contaminated by selenate, methylmercury, or combination of the two have substantial implications for the ecology, population dynamics, and sustainability of M. scalaris populations. If these results can be extrapolated to other arthropod detritivores, ecosystem food-web function may be substantially affected.

Animals↗
PubMed2006

Selenium and other trace elements in aquatic insects in coal mine-affected streams in the Rocky Mountains of Alberta, Canada.

We determined levels of Se, As, Cd, Pb, and Zn in aquatic insects at coal mine-impacted and reference sites in streams in the Rocky Mountain foothills of west central Alberta from 2001-2003. Selenium levels were greater at coal mine-impacted sites than at reference sites in caddisflies but not in mayflies or stoneflies. Arsenic levels were greater at coal mine-impacted sites than at reference sites in caddisflies and stoneflies but not in mayflies. Zn levels were higher at coal mine-impacted sites than at reference sites in all three groups of insects. At coal mine-impacted sites, Se levels in mayflies and caddisflies were greater than those in stoneflies while at reference sites mayflies contained greater concentrations of Se than either caddisflies or stoneflies. Arsenic levels in mayflies were greater than those in caddisflies at reference and coal mine-impacted sites and were greater than those in stoneflies at reference sites. At both types of sites Cd differed amongst insect taxa in the order of mayflies > caddisflies > stoneflies. The same was true of Zn at coal mine-affected sites. At reference sites, stoneflies had greater concentrations of Zn than both mayflies and caddisflies. At both types of sites, Pb levels were greater in mayflies and caddisflies than they were in stoneflies. Of the five trace elements considered in this study, only Se was sufficiently elevated in aquatic invertebrates to be of potential concern for consumers such as fish and aquatic birds. Such was the case at both coal mine-impacted and reference sites.

Alberta↗
PubMed2000

Effects of sustained-release methoprene and a combined formulation of liquid methoprene and Bacillus thuringiensis israelensis on insects in salt marshes.

Aquatic insects are an important component of the food web in salt marshes, therefore it is necessary to test whether pesticides used to control mosquitoes in salt marshes are safe for nontarget insects. We tested the nontarget effects of a combined formulation (duplex) of Bacillus thuringiensis israelensis (B.t.i.) and liquid methoprene (an insect development regulator) or sustained-release methoprene pellets (Altosid(R) pellets) by applying these materials to replicated salt marsh ponds at maximum label rates. Untreated ponds served as controls. We measured effects of the pesticides by rearing immature mosquitoes (Aedes dorsalis) and water boatmen (Trichocorixa reticulata) in predator-exclusion cages and by monitoring uncaged populations of invertebrates using replicated sweep-net samples. Both pesticides killed caged mosquitoes, and the activity of the Altosid(R) pellets continued through 99 days. There were no detectable effects of either pesticide on the survival or maturation of T. reticulata, or on abundances of uncaged invertebrates. The long-term activity of the pellets could help minimize mosquito abatement activity in salt marshes where there are breeding birds or endangered species. However, other studies suggest that this advantage needs to be balanced against the risks that sustained-release formulations could lead to development of resistance in mosquitoes or that initially undetected nontarget effects could build over time.

Aedes↗
PubMed2006

Secretory production system of bionanocapsules using a stably transfected insect cell line.

Bionanocapsules (BNCs) are hollow nanoscale particles composed of L protein of the hepatitis B virus surface antigen that represent specific affinity for human hepatocytes. BNCs can transfer genes and drugs into human hepatocytes efficiently and specifically. BNC can be expressed in yeast cells. In this study, we developed a new L particle production system using a stably transfected insect cell line. For this purpose, we established a host-vector system using the Trichoplusia ni insect cell line. L particles were efficiently secreted by the overexpression of the L protein, which was fused to the secretion signal peptide. The concentration of L particles was reached approximately 1.7 microg/ml in 5 days during cultivation in a serum-free medium without antibiotic selective pressure. The production of L particles was maintained for at least 75 days. The secretory production of L particles facilitated their easy purification by chromatography. Furthermore, it was demonstrated that purified L particles can transfect only human hepatocytes. Therefore, an insect cell expression system is an attractive tool for the production of BNC.

Animals↗
PubMed2001

Investigation of sequential behavior of carboxyl protease and cysteine protease activities in virus-infected Sf-9 insect cell culture by inhibition assay.

Proteases produced during the culture of Spodoptera frugiperda Sf-9 cells infected with Autographa californica nuclear polyhedrosis virus (AcNPV) were assayed with various protease inhibitors. This inhibitory analysis revealed that: (1) carboxyl and cysteine proteases were predominantly produced by the insect cells infected with recombinant AcNPV, the gene of which encoded a variant of green fluorescent protein in a portion of the polyhedrin gene of the baculovirus, and (2) the protease activity was almost completely blocked by pepstatin A (carboxyl protease inhibitor) and E64 (cysteine protease inhibitor) in an additive manner in the presence of EDTA. Utilizing the additive property of the inhibitors, the inhibition-based protease assay discriminated between the two protease activities and elucidated the sequential behavior of the carboxyl and cysteine proteases produced in the virus-infected Sf-9 cell culture. The carboxyl protease(s) existed in the virus-infected cells all the time and their level in the medium continuously increased. Uninfected cells also contained a carboxyl protease activity, the level of which was similar to that of the virus-infected cells. At a certain time after virus infection, the cysteine protease activity was largely increased in the virus-infected cells and a significant amount of the protease(s) was released into the medium, due to the cell membranes losing their integrity. The behavior of intracellular and extracellular cysteine protease activities coincided with that of a recombinant protein whose expression was under the control of the viral polyhedrin promoter. Similar examinations with wt-AcNPV-infected and uninfected insect cells showed that the inhibition-based protease assay was useful for analyzing the carboxyl protease and cysteine protease activities emerging in the insect cell (Sf-9)/baculovirus expression system.

Animals↗
PubMed2004

Nucleotide sequence variation does not relate to differences in kinetic properties of neutral trehalase from the insect pathogenic fungus Metarhizium anisopliae.

Genetic variability in a putative virulence factor, the neutral trehalase ( Ntl) gene, was examined in strains of the insect pathogenic fungi Metarhizium anisopliae and Metarhizium flavoviride by restriction fragment length polymorphism (RFLP). The Ntl gene was sequenced from four of these strains that showed dissimilar RFLP patterns. Enzyme kinetic experiments were also performed on the partially purified neutral trehalase in order to assess whether nucleotide changes in these strains related to differences in enzyme catalytic function (i.e., Km, Vmax, and Kcat). Finally, the Metarhizium strains were assessed in bioassays against waxworm larvae in order to relate nucleotide variation with Ntl enzyme kinetics and insect virulence. The greatest RFLP variation was observed with Rsa1. M. flavoviride was found to be most dissimilar in RFLP patterns when compared with the M. anisopliae strains. RFLP patterns for Ntl were diagnostic markers for previously studied genetic groups of M. anisopliae. Comparisons of Ntl sequences showed that the introns were found to be more variable (6.2%) than the exons (3.1%). Comparisons of the translated nucleotide codons showed high levels (91%) of synonymous sequence variation between strains. Another fraction of the remaining mutations was neutral, resulting in amino acid substitutions with similar functions. The neutral trehalase was partially purified by preparative isoelectric focus, revealing a single band of enzyme activity as assessed by analytical isoelectric focusing (pI ca. 5). Kinetic properties of the neutral trehalases revealed no differences between the M. anisopliae strains, while the M. flavovoride had a lower Kcat/Km. However, there was lower virulence in one strain that showed Ntl enzyme kinetic properties that were similar to the other strains, suggesting that factors other than neutral trehalase may be responsible for delimiting virulence in this insect pathogenic fungi. Although there is nucleotide variation in genes involved in pathogenicity, this variation is mostly neutral in nature, and there is strong stabilizing selection to maintain enzyme function.

Amino Acid Substitution↗
PubMed1997

Detection and molecular analysis of plant- and insect-associated bacteria harboring aconitate isomerase involved in biosynthesis of trans-aconitic acid as antifeedant in brown planthoppers.

The activity of aconitate isomerase, which is involved in the biosynthesis of trans-aconitic acid as antifeedant in brown planthoppers, was detected in Pseudomonas fluorescens LRB3W1 and Pseudomonas putida MAFF301685 but not in Pseudomonas putida MAFF301684. The enzyme activity was induced in the presence of trans-aconitate, and therefore bacteria showing the enzyme activity were easily detected by their ability to grow on the minimal medium containing trans-aconitate as the sole carbon source (ACO agar medium). Experiments on growth of plant- or insect-associated bacteria on ACO agar medium showed that most of the Gram-negative bacteria displayed the aconitate isomerase activity unlike most of the Gram-positive bacteria isolated mainly from insects. Mini-Tn5 transposon derivatives of P. fluorescens LRB3W1 lacking completely or partially their ability to grow on ACO agar medium were obtained. Southern blot analysis with a mini-Tn5 DNA probe definitely showed that the genes responsible for the biosynthesis of aconitate isomerase present on chromosomal DNA. Thus, it was suggested that genes for aconitate isomerase biosynthesis are commonly present in Gram-negative plant- or insect-associated bacteria, and also the DNA fragments including the genes were detected in P. fluorescens LRB3W1.

Aconitic Acid↗
PubMed2006

The host acts as a genetic bottleneck during serial infections: an insect-fungal model system.

The genetic variation of a pathogen population is a pivotal component of pathogen evolution, having important implications for emerging diseases, nosocomial infections, and laboratory subculturing practices. Furthermore, it is undoubtedly altered during infection of a host. We address this issue using an insect-fungal model system to examine the influence of serial host passage on the genetic variation of a pathogen population. Using amplified fragment length polymorphism, a strain of the opportunistic fungus, Aspergillus flavus, showing initially 98% genetic similarity, was assessed for changes in genetic diversity during repeated passage through Galleria mellonella larvae and compared to that of a parallel population serially subcultured on artificial media. In two independent trials, the genetic diversity of the population passed through the insect dropped significantly, while the genetic variation of the population subcultured on media increased or remained unchanged. However, there were no changes in virulence or the production of protease or aflatoxin, indicating an apparent lack of selection. We suggest that the insect acted as a genetic bottleneck, reducing the genetic diversity of the A. flavus population. The ability of a host to produce a genetic bottleneck in a pathogen population impacts our understanding of emerging diseases, nosocomial infections, and laboratory subculturing practices.

Animals↗
PubMed2002

Colour in the eyes of insects.

Many insect species have darkly coloured eyes, but distinct colours or patterns are frequently featured. A number of exemplary cases of flies and butterflies are discussed to illustrate our present knowledge of the physical basis of eye colours, their functional background, and the implications for insect colour vision. The screening pigments in the pigment cells commonly determine the eye colour. The red screening pigments of fly eyes and the dorsal eye regions of dragonflies allow stray light to photochemically restore photoconverted visual pigments. A similar role is played by yellow pigment granules inside the photoreceptor cells which function as a light-controlling pupil. Most insect eyes contain black screening pigments which prevent stray light to produce background noise in the photoreceptors. The eyes of tabanid flies are marked by strong metallic colours, due to multilayers in the corneal facet lenses. The corneal multilayers in the gold-green eyes of the deer fly Chrysops relictus reduce the lens transmission in the orange-green, thus narrowing the sensitivity spectrum of photoreceptors having a green absorbing rhodopsin. The tapetum in the eyes of butterflies probably enhances the spectral sensitivity of proximal long-wavelength photoreceptors. Pigment granules lining the rhabdom fine-tune the sensitivity spectra.

Animals↗
PubMed2004

Mechanisms of stick insect locomotion in a gap-crossing paradigm.

Locomotion of stick insects climbing over gaps of more than twice their step length has proved to be a useful paradigm to investigate how locomotor behaviour is adapted to external conditions. In this study, swing amplitudes and extreme positions of single steps from gap-crossing sequences have been analysed and compared to corresponding parameters of undisturbed walking. We show that adaptations of the basic mechanisms concern movements of single legs as well as the coordination between the legs. Slowing down of stance velocity, searching movements of legs in protraction and the generation of short steps are crucial prerequisites in the gap-crossing task. The rules of leg coordination described for stick insect walking seem to be modified, and load on the supporting legs is assumed to have a major effect on coordination especially in slow walking. Stepping into the gap with a front leg and antennal contact with the far edge of the gap provide information, as both events influence the following leg movements, whereas antennal "non-contact" seems not to contain information. Integration of these results into the model of the walking controller can improve our understanding of insect locomotion in highly irregular environments.

Animals↗
PubMed1999

Responses of the digestive tract of the omnivorous northern brown bandicoot, Isoodon macrourus (Marsupialia: Peramelidae), to plant- and insect-containing diets.

The gastrointestinal tract of omnivores such as bandicoots (Marsupialia: Peramelidae) must be able to process foods as different as invertebrates, fungi and plant material. We studied the mechanisms involved in the utilisation by captive northern brown bandicoots (Isoodon macrourus) of insect larvae and milled lucerne (Medicago sativa) hay incorporated into a basal diet of a commercial small carnivore mix. Animals on the plant-basal mix digested less dry matter, energy, lipid, fibre and total nitrogen, but consumed 79% more dry matter than those on the insect-basal mix. Consequently intake of digestible energy (i.e. energy absorbed) was not significantly different between diets. Mean retention time (MRT, the mean time a marker remains in the tract) of a large particle marker was shorter on the plant-basal mix, reflecting its higher intake, but MRT of a solute marker was not significantly different between diets. Consequently the solute marker was retained longer than the particle marker on the plant-basal mix, indicating selective retention of solutes and very small particles in the caecum on this diet. This was confirmed by a higher proportion of small particles in the caecum than the distal colon of road-killed I. macrourus. Thus the main responses by I. macrourus to the plant-basal mix appeared to be an increase in gastrointestinal tract capacity (from radiographic evidence), selective retention of solutes and very small particles in the caecum, and facilitated passage of less tractable large particles through the colon. As a consequence, food intake was higher on the plant-basal mix, which compensated for its lower digestibility, and intake of digestible energy was similar to that on the insect-basal mix. This considerable flexibility of the morphologically rather simple digestive tract of northern brown bandicoots helps to explain their ability to cope with naturally variable diets consisting of mainly invertebrates in summer to much more plant and fungal material in winter, and to survive in nutritionally dynamic environments such as heathlands where there can be dramatic changes in food type and availability following periodic wildfires.

Animals↗
PubMed2004

Neurogenesis in the chilopod Lithobius forficatus suggests more similarities to chelicerates than to insects.

In a recent comparative study on neurogenesis in the diplopod Glomeris marginata we have shown that the millipede and the spider share several features that cannot be found in homologous form in insects and crustaceans. The most distinctive difference is that groups of neural precursors are singled out from the neuroectoderm of the spider and the diplopod, rather than individual cells (i.e. neuroblasts) as in insects or crustacean. This observation constitutes the first morphological indication for a close myriapod/chelicerate relationship that has otherwise only been suggested by molecular phylogenetic analysis. To see whether the pattern of neurogenesis described for the diplopod is representative for myriapods, we analysed neurogenesis in the basal chilopod Lithobius forficatus. We show here that groups of cells invaginate from the chilopod neuroectoderm at strikingly similar positions as the invaginating cell groups of the diplopod and the spider. Furthermore, the expression patterns of the proneural and neurogenic genes reveal more similarities to the chelicerate and the diplopod than to insects. Thus, chelicerates and myriapods share the developmental mechanism for neurogenesis, either because they are true sister groups, or because this reflects the ancestral state of neurogenesis in arthropods.

Amino Acid Sequence↗
PubMed2003

Immunocytochemical distribution of pigment-dispersing hormone in the cephalic ganglia of polyneopteran insects.

Material detectable with antisera to the pigment-dispersing hormone (PDH) is regarded as a component of the circadian clock residing in some insects in the optic lobe. This paper demonstrates that the position of the PDH-positive neurones and the course of their processes are similar in all representatives of the insect cohort Polyneoptera. A basic morphological pattern, which includes the proximal frontoventral (Pfv), distal posteriodorsal (Dpd) and posterioventral (Dpv) clusters of PDH-positive neurones, was found in the examined species of locusts, crickets, walking sticks, cockroaches, earwigs and termites. The Pfv cluster is located close to the accessory medulla and usually consists of a set of smaller and a set of larger perikarya. The Dpd and Dpv clusters occupy a dorsal and a ventral position, respectively, at the distal edge of the medulla. These clusters are lacking in stonefly and praying mantid species. The fan-like arrangement of PDH-positive fibres within the frontal medulla face (the locusts and the praying mantid have an additional, smaller fan on the posterior medulla face) is another characteristic feature of Polyneoptera. One (two in the locusts and the praying mantid) nerve bundle runs from the optic lobe to the lateral protocerebrum where it ramifies. One branch gives rise to a fibre network frontally encircling brain neuropile in the area of mushroom bodies. One thin fibre in the crickets and the earwig, and several thicker and anastomosing fibres in the other insects, connect the brain hemispheres. The arrangement of other PDH-positive structures specifies taxa within Polyneoptera. Specific features comprise the presence of PDH-positive perikarya in protocerebrum (walking stick and termite), deutocerebrum (cricket, walking stick, and one cockroach species), tritocerebrum (another cockroach species), and the suboesophageal ganglion (cricket, walking stick and termite). In the walking stick and the termite, PDH-positive fibres pass from the cephalic to the frontal ganglion and from there via the recurrent nerve to the corpora cardiaca where they make varicosities indicative of peptide release into the haemolymph.

Animals↗
PubMed2005

Cell-death mechanisms in the IPLB-LdFB insect cell line: a nuclear located Bcl-2-like molecule as a possible controller of 2-deoxy-D-ribose-mediated DNA fragmentation.

In the IPLB-LdFB insect cell line, oncosis and apoptosis are the two pre-mortal processes, whereas necrosis is the post-mortem condition. As found in mammals, adenosine triphosphate depletion of insect cells by oligomycin A induces oncosis. The apoptotic inducer 2-deoxy-D: -ribose (dRib) provokes cell death through an intrinsic apoptotic pathway similar to that observed in mammalian models and results in oligonucleosomal DNA fragmentation. The addition to insect cells of an anti-Bcl-2 polyclonal antibody known to prevent dRib-mediated apoptosis abolishes DNA fragmentation, whereas cytochrome c release and the increase in a caspase 3-like activity are still detectable. These and previous findings suggest a double role for the Bcl-2-like molecule in IPLB-LdFB, i.e. the maintenance of mitochondrial integrity and the control of apoptotic machinery at the nuclear level.

Animals↗
PubMed2003

Positive and negative effects of leaf shelters on herbivorous insects: linking multiple herbivore species on a willow.

We experimentally examined the effects on other herbivorous insects of leaf shelters constructed by lepidopteran larvae on a willow, Salix miyabeana. Several insect species occupied the vacant leaf shelters. Our experiment using artificial leaf shelters showed that the number of aphids increased with the number of artificial leaf shelters on a shoot, as did the numbers of three ant species ( Camponotus japonicus, Lasius hayashi, and Myrmica jessensis) that entered leaf shelters to collect aphid honeydew. To determine the ant-mediated effect of leaf shelters on herbivorous insects that do not use leaf shelters, we transferred newly hatched larvae of a common leaf beetle, Plagiodera versicolora, to the leaves of shoots with and without artificial leaf shelters. One day after the transfer, larval survival rate was significantly lower on shoots with shelters than on those without shelters, and shoots with shelters had significantly more ants than did shoots without shelters. Our field experiments demonstrated clearly that shelter-making lepidopteran larvae increased the abundance of both aphids and ants and decreased the survival rate of leaf beetle larvae, probably because the larvae were removed by ants that were attracted to the leaf shelters by the aphid colonies.

Animals↗
PubMed2005

Spatial variation in insect community and species responses to habitat loss and plant community composition.

Several experimental studies have examined species responses to manipulations of habitat area and spatial arrangement, but plant composition and spatial variation in species distributions also affect animal responses to habitat alteration. We used an experimental approach to study the combined effects of habitat area, edge, and plant community composition on the spatial structure of insect species richness and composition. The abundance of three guilds (herbivores, predators and parasitoids) and individual species were also analyzed. Habitat patches were created that differed in area and edge by selectively mowing portions of 15 mx15 m plots in a 1.7-ha old field. Spatial and environmental variables were used to predict insect responses in separate multiple regression and ordination models. The variation in species responses due to spatial and environmental variables was then partitioned by combining these variables into an overall regression or ordination. Spatial and environmental variables contributed similar percentages to the total variance in insect species richness, abundance or composition. No significant effects of habitat area were observed in any response variable. Herbivore abundance showed positive responses to legume or grass cover, as well as spatial variation that was unrelated to environmental variables. Predators and parasitoids had greater effects of plant species richness and habitat edge, and less unexplained spatial variation. Individual species differed in their responses to plant variables, depending on host specialization or intraspecific aggregation. Our study highlights the importance of plant community composition and spatial variation apart from environmental variables. Spatial variation stems both from species responses to environmental features as well as species differences in habitat specialization and intraspecific aggregation.

Animals↗
PubMed2006

Stream insect occupancy-frequency patterns and metapopulation structure.

An understanding of the distribution patterns of organisms and the underlying factors is a fundamental goal of ecology. One commonly applied approach to visualize these is the analysis of occupancy-frequency patterns. We used data sets describing stream insect distributions from different regions of North America to analyze occupancy-frequency patterns and assess the effects of spatial scale, sampling intensity, and taxonomic resolution on these patterns. Distributions were dominated by satellite taxa (those occurring in or=90% of sites) determined the overall modality of occupancy-frequency patterns. The proportions of satellite taxa increased with spatial scale and showed positive relationships with sampling intensity (r2=0.74-0.96). Furthermore, analyses of data sets from New York (USA) showed that generic-level assessments underestimated the satellite class and occasionally shifted occupancy-frequency distributions from unimodal to bimodal. Our results indicate that, regardless of species- or generic-level taxonomy, stream insect communities are characterized by satellite species and that the proportion of satellite species increases with spatial scale and sampling intensity. Thus, niche-based models of occupancy-frequency patterns better characterize stream insect communities than metapopulation models such as the core-satellite species hypothesis.

Animals↗
PubMed2006

Catalase effect on cell death for the improvement of recombinant protein production in baculovirus-insect cell system.

Baculovirus expression vector system (BEVS) in host insect cells is a powerful technology to produce recombinant proteins, as well as virus-like particles (VLP). However, BEVS is based on baculovirus infection, which limits the recombinant protein production by inducing insect cell death. Herein a new strategy to enhance cell life span and to increase recombinant protein production was developed. As baculovirus infection induces cellular oxidative stress, the ability of several antioxidants to inhibit cell death was tested during infection. The production of rotavirus structural proteins was used as model to analyse this new strategy. We found that only catalase is able to partially prevent cell death triggered by baculovirus infection and to inhibit lipid peroxidation. An increase in recombinant protein production was coupled with the partial cell death inhibition. In summary, the addition of catalase is a promising strategy to improve recombinant protein production in BEVS, by delaying insect cell death.

Animals↗