Histopathological effects of tannic acid on the midgut epithelium of some aquatic Diptera larvae

The impact of tannins on larval Nematocera was investigated by an extensive survey of the relative toxicity of tannic acid in Diptera larvae representative of mosquito communities from alpine hydrosystems (Culicidae, Chaoboridae, Chironomidae, and Simuliidae) together with a nonindigenous vector competent Culicidae species. Bioassays indicate that exposure to tannic acid at concentrations from 0.25 to 4 mM is deleterious for Culex pipiens, Simulium variegatum, and Chironomus annularius, but not for Aedes, Anopheles, Culiseta, and Chaoborus species. Histopathological observations reveal that, among the target organs of tannic acid, mainly the midgut epithelium is affected by treatment. However, the extent of degeneration varies according to the taxon, the duration of the treatment, and the concentrations assayed. The vulnerability of epithelial cells differs among cell types, clear cells of the anterior midgut showing symptoms of intoxication before dark cells of the posterior midgut. The toxic effects of tannic acid are discussed, particularly in comparison to those of insecticidal bacteria, in order to evaluate the potential for use of tannins in the regulation of larval populations of dipteran pests.     

Differential toxicity of leaf litter to dipteran larvae of mosquito developmental sites

The relative toxicity of leaf litter to nematocerous dipteran larvae characteristic of mosquito developmental sites was investigated. Culicidae, Chironomidae, and Simuliidae taxa originating from alpine hydrosystems were tested together with two laboratory nonindigenous culicid taxa. Bioassays indicate that ingestion of 10-month-old decaying leaves from Alnus glutinosa, Populus nigra, and Quercus robur by larvae is more deleterious for Aedes aegypti, A. albopictus, Culex pipiens, Simulium variegatum, and Chironomus annularius than for A. rusticus. Histopathological observations reveal that the midgut epithelium is the main target organ of the toxic effect of dietary leaf litter, which appears to be stronger than that of previously reported tannic acid. There is a general response of the nematocerous larval midgut epithelium to dietary tannins-phenolic compounds: clear cells of the anterior midgut showing symptoms of intoxication before dark cells of the posterior midgut.     

Crustacean biodiversity as an important factor for mosquito larval control

Newly established ponds, which are highly dynamic systems with changing levels of biological interactions among species, are common larval mosquito habitats. We investigated the impact of crustacean abundance and taxa diversity on mosquito oviposition and larval development. The effects of the biological larvicide Bacillus thuringiensis israelensis (Bti) on mosquito larvae were monitored according to fluctuations in crustacean communities. Populations of the mosquito Culex pipiens colonized artificial ponds that contained crustacean communities at different time points of colonization by crustaceans: 1) ‘no colonization’ (no crustaceans), 2) ‘simultaneous colonization’ by crustaceans and mosquitoes, and 3) ‘head‐start colonization’ by crustaceans (preceding colonization by mosquitoes). All types of ponds were treated with three concentrations of Bti (10, 100, or 1,000 µg/liter). Colonization of all ponds by Cx. pipiens (in terms of oviposition, larval abundance, and larval development) decreased significantly with increasing diversity of crustacean taxa. The total abundance of crustaceans had a minor effect on colonization by Cx. pipiens. The presence of crustaceans increased the sensitivity of Cx. pipiens larvae to Bti treatment by a factor of 10 and delayed the time of recolonization. This effect of Bti was relevant in the short term. In the long term, the presence of Cx. pipiens was determined by crustacean biodiversity.     

Mosquito species composition and phenology (Diptera,Culicidae) in two German zoological gardens imply different risks of mosquito‐borne pathogen transmission

Due to their large diversity of potential blood hosts, breeding habitats, and resting sites, zoological gardens represent highly interesting places to study mosquito ecology. In order to better assess the risk of mosquito‐borne disease‐agent transmission in zoos, potential vector species must be known, as well as the communities in which they occur. For this reason, species composition and dynamics were examined in 2016 in two zoological gardens in Germany. Using different methods for mosquito sampling, a total of 2,257 specimens belonging to 20 taxa were collected. Species spectra depended on the collection method but generally differed between the two zoos, while species compositions and relative abundances varied seasonally in both of them. As both sampled zoos were located in the same climatic region and potential breeding sites within the zoos were similar, the differences in mosquito compositions are attributed to immigration of specimens from surrounding landscapes, although the different sizes of the zoos and the different blood host populations available probably also have an impact. Based on the differences in species composition and the various biological characteristics of the species, the risk of certain pathogens to be transmitted must also be expected to differ between the zoos.     

Mosquitoes as Bioindicators of Forest Degradation in Southeastern Brazil,a Statistical Evaluation of Published Data in the Literature

The data of 20 mosquito surveys performed in areas of tropical forest in southeastern Brazil were analyzed by means of multivariate statistical procedures (correspondence analysis and cluster analysis). The results are interpreted in relation to the degree of degradation reported for each forest in the collecting sites, allowing the selection of species or groups of species that act as good indicators of local environmental changes. By this approach the different localities were scaled along a gradient of anthropogenic modifications correlated with a particular mosquito fauna. The resulting model allows to classify different woods in southeastern Brazil according to their state of preservation, by means of their mosquito species. Four bioindicators for the particular levels of forest degradation in southeastern Brazil are proposed: Kerteszia, Aedes scapularis, Mansoniini and Haemagogus.     

Comparative biodiversity of crustaceans and aquatic insects from various water body types in coastal Mediterranean wetlands

Coastal wetlands are characterized by a high biodiversity. At the same time, biodiversity is one of the main criteria used to establish protection policy priorities, or to propose management actions. In this study, crustacean and aquatic insect species richness in the Empordà wetlands was investigated. These two groups contribute in an important way to the total biodiversity, and still they are seldom taken into account in the management of natural areas. Representative samples (38 points) of all aquatic water body types in the Empordà wetlands were taken monthly (dip net with 250 μm mesh). Sampling was carried out between 1996 and 2000, but until present, only qualitative data have been extracted. A rich fauna of 125 crustacean taxa and 295 aquatic insect taxa were found. Some environments were characterized by low richness and high singularity (isolated artesian freshwater springs), some by high richness and high singularity (estuarine waters, brackish and meso-eutrophic freshwater wetlands), and others by low richness and low singularity (hypertrophic freshwater wetlands and hyperhaline wetlands). Factors determining singularity and richness are discussed. Comparison with crustacean richness of other western Mediterranean wetlands showed a similar high species richness in our study sites, probably due to high spatial heterogeneity of these areas.     

Temporal and Taxonomic Variability in Response of Fauna to Riparian Restoration

Evaluating the success of restoration projects requires well‐designed studies. Among the decisions that need to be made are what taxonomic groups to study and when to conduct the monitoring. To explore how these decisions can influence assessments of restoration success, we examined species richness and composition data collected over several years on different terrestrial fauna (landbirds, rodents, bees, and beetles) at Sacramento River restoration and remnant riparian sites. Our selection of study organisms enabled us to ask whether variability in species richness among restoration sites is less for vagile taxa than for sedentary taxa, and if invertebrates display greater variability among sites than vertebrates. Our results demonstrate that responses to restoration can vary depending upon the season when it is assessed, and the taxa that are studied. For all taxa except bees, there was considerable variability in the relative performance of taxa at restoration sites from one sampling date to the next, such that the relative ranking of the sites often changed dramatically. Comparisons of β ‐diversity (variability in species richness across sites) revealed that certain taxonomic groups were more spatially variable in their response to restoration than others. Among vertebrates, sedentary taxa (rodents) had significantly higher variability in species richness across sites than highly vagile taxa (birds); however, no such pattern was observed for invertebrates. Overall, vertebrates had lower variability than invertebrates, suggesting that evaluations of restoration success based on a few better‐known taxonomic groups (e.g., birds, rodents) may be inadequate to represent the biodiversity response of other groups (e.g., insects).     

Comparative histopathology of some Diptera and Crustacea of aquatic alpine ecosystems, after treatment with Bacillus thuringiensis var. israelensis

Species of Diptera (larval Culicidae, Chironomidae and Simuliidae) and Crustacea (cladoceran adults) that are representative of the fauna of aquatic alpine ecosystems are routinely treated with Bacillus thuringiensis var. israelensis (Bti) for mosquito control. The toxicity of Bti on these organisms was investigated. Bioassays indicated that Bti used at the concentration for operational field application is deleterious to all dipteran species, but not to Cladocera. Histopathological observations reveal that, in all cases, the midgut epithelium is affected by Bti treatment. However, the vulnerability of epithelial cells to the microbial insecticide is different from one cell-type to another, clear cells being more vulnerable than dark cells. Because of the concentration of clear cells within the anterior midgut of dipteran larvae, this region appears to be the first to show symptoms of intoxication through enhancing a natural process of cell turnover. The relative importance of such a vulnerable region in the midgut of dipteran larvae may account for the general efficacy of Bti to these species. Its harmlessness to Cladocera may be correlated to the relative scarcity of clear cells and their patchy distribution along the whole midgut together with important cellular renewal capacity of the epithelium.     

The first report of Aedes (Stegomyia) albopictus in Haiti

Aedes albopictus was found in six of the 10 departments of Haiti and in 14 of the 35 communes surveyed. The survey found the larvae of Ae. albopictus in 13 different types of containers. Used tires and tins were by far the most common breeding sites used by this mosquito species. At the breeding sites, Ae. albopictus was associated with other mosquito species, such as Aedes aegypti, Culex nigripalpus and Aedes mediovittatus. The highest proportion of association was with Ae. aegypti. This study represents the first report of Ae. albopictus in Haiti.     

Molluscs and echinoderms under boulders: Tests of generality of patterns of occurrence

Quantifying and understanding the spatial patterns of variation in diversity and abundances of intertidal animals is receiving increased attention because causal models must focus on the scales at which individual organisms interact. Intertidal boulders are complex and naturally fragmented habitats and many species on boulders are absent from the matrix on which boulders lie and which separates individual boulders. This study builds on quantified observations of molluscs and echinoderms living underneath boulders in a sheltered boulder-field in New South Wales, Australia, which documented that, at the same tidal height, most of the variation in these fauna was at the scale of individual boulders, or between replicate sites only 20 m apart. Here, six specific models and hypotheses about spatial and temporal variability arising from that study were tested in 4 boulder-fields along 200 km of coast. Most variation was at the scale of individual boulders and between sites within boulder-fields, with some sites having similar fauna to sites in other boulder-fields and sites in the same boulder-fields having very different fauna. Although individual taxa were very variable in abundance, measures of the assemblages remained relatively consistent through time. Both rare and abundant species were extremely overdispersed, only being found on a minority of boulders and with very large abundances on some of these. The degree of overdispersion varied among boulder-fields for some taxa and not others, but there was no generality of patterns for a range of taxa in the same boulder-field, nor for individual taxa in different locations. Nevertheless, over 95% of the 1200 boulders sampled were occupied by at least one species. These extreme patterns of partitioning of habitat are discussed briefly in terms of managing these complex habitats.     

The structure of a high latitude plant-flower visitor system: the dominance of flies

The species richness of insect flower visitors to all angiosperms at a subarctic-alpine site in northern Sweden was described and the plant-flower visitor matrix was analysed and compared to other high latitude systems and with systems from lower latitudes. In the habitat, 23 plant species had a total of 242 interactions with 388 flower-visiting insects, belonging to 118 taxa. Connectance of the plant-flower visitor matrix was 8.9. Comparing our findings with other studies, we get that the proportion of dipteran species of the total pollinator fauna increases with latitude but that the proportions of species of Diptera, Hymenoptera and Lepidoptera do not vary significantly among high latitude systems. Muscidae and Empididae were more abundant and generalised than other dipteran families visiting flowers in the arctic, their proportions of the total Diptera fauna increase with latitude and they are the most widespread families of flower-visiting insects in the arctic. Several Muscidae species are typical to alpine habitats in the arctic-subarctic zone. These species have special pollen feeding behaviour and an elongated proboscis, which improves access to closed flowers.
Compared to other published pollination system studies, the connectance of low latitude systems ranges between 3.4 and 28.1, whereas high latitude and high altitude systems vary between 8.6 and 19 (-60).     

Identifying key environmental factors related to plant and crustacean assemblages in Mediterranean temporary ponds

The current interest in Mediterranean temporary wet habitats, considered to be habitats of European Community Interest, is mainly due to their characteristic flora and fauna. Several contributions characterize each of these two components separately, but considering them simultaneously could reveal possible interactions and a more complete view of the habitat that would be useful to improve conservation measures. This paper investigates crustacean and plant assemblages in six Mediterranean temporary ponds and their relationship with several environmental variables. Significant positive relationships were found between species richness and Shannon diversity index of plant and crustacean assemblages. Crustaceans had a higher similarity among ponds than plants and, consequently, each pond had a more characteristic assemblage of plants than of crustaceans. The two groups showed a different sensitivity to environmental factors and only two factors affected both: altitude and surface area of the wet system. Disturbances (e.g. grazing by cattle) and pond size were very important for plants, whereas they were irrelevant for crustaceans. On the other hand, distance to the nearest pond, hydroperiod length, and water nitrogen were only important for crustaceans. Although similar trends on richness and diversity were observed for both biotic groups, the use of only one of them for conservation programs would not be sufficient. Our results suggest that simultaneously taking into account several community components would result in a better understanding of ecosystem functionality.     

Diversity and seasonal abundances of mosquitoes at potential arboviral transmission sites in two different climate zones in Switzerland

Pathogens of medical or veterinary significance that are transmitted by mosquitoes (Diptera: Culicidae) are (re‐)emerging in Europe [e.g. West Nile virus (WNV), Dirofilaria nematodes]. Little is known about the spatiotemporal abundances of mosquito species in Switzerland. Therefore, mosquito population dynamics were investigated, focusing on areas of risk for sylvatic or synanthropic transmission, such as natural sites and suburban sites on either side of the Alpine crest. Repeated collections were made using Centers for Disease Control (CDC) traps, juvenile sampling and ovitrapping. A total of 122 831 mosquito specimens of 21 taxa were identified. Levels of mosquito species richness were similar at suburban sites and in natural zones in Switzerland. Mosquito abundances and seasonality were analysed with generalized linear mixed models based on 382 CDC trap samples (29 454 females) and revealed Aedes annulipes/cantans, Aedes geniculatus, Aedes japonicus, Aedes sticticus, Aedes vexans, Coquillettidia richiardii and Culex pipiens/torrentium as the dominant species overall. Abundances of these species were season‐dependent in most cases. There was an effect of site with regard to abundance (higher in natural zones), but not with respect to seasonality. Together with data on vector competence and the host preferences of different species, the present data contribute to assessments of risk for pathogen transmission. For example, both natural and suburban environments seem feasible as sites for amplification cycles of WNV and transmission to mammals.     

A three-genome phylogeny of malaria parasites (Plasmodium and closely related genera): evolution of life-history traits and host switches

Phylogenetic analysis of genomic data allows insights into the evolutionary history of pathogens, especially the events leading to host switching and diversification, as well as alterations of the life cycle (life-history traits). Hundreds, perhaps thousands, of malaria parasite species exploit squamate reptiles, birds, and mammals as vertebrate hosts as well as many genera of dipteran vectors, but the evolutionary and ecological events that led to this diversification and success remain unresolved. For a century, systematic parasitologists classified malaria parasites into genera based on morphology, life cycle, and vertebrate and insect host taxa. Molecular systematic studies based on single genes challenged the phylogenetic significance of these characters, but several significant nodes were not well supported. We recovered the first well resolved large phylogeny of Plasmodium and related haemosporidian parasites using sequence data for four genes from the parasites' three genomes by combining all data, correcting for variable rates of substitution by gene and site, and using both Bayesian and maximum parsimony analyses. Major clades are associated with vector shifts into different dipteran families, with other characters used in traditional parasitological studies, such as morphology and life-history traits, having variable phylogenetic significance. The common parasites of birds now placed into the genus Haemoproteus are found in two divergent clades, and the genus Plasmodium is paraphyletic with respect to Hepatocystis, a group of species with very different life history and morphology. The Plasmodium of mammal hosts form a well supported clade (including Plasmodium falciparum, the most important human malaria parasite), and this clade is associated with specialization to Anopheles mosquito vectors. The Plasmodium of birds and squamate reptiles all fall within a single clade, with evidence for repeated switching between birds and squamate hosts.     

Do eel parasites reflect the local crustacean community? A case study from the Rhine River system

In 2003, the parasite fauna of 197 European eels Anguilla anguilla, captured at three different locations (Laufenburg, Karlsruhe and Beneeden Leeuwen) in the River Rhine, was analysed. The eels harboured a total of 18 species, among them the protozoa (Myxidium giardi, Myxobolus kotlani and Trypanosoma granulosum), acanthocephalans (Acanthocephalus anguillae, Acanthocephalus lucii, Echinorhynchus truttae, Pomphorhynchus laevis), nematodes (Paraquimperia tenerrima, Pseudocapillaria tomentosa, Camallanus lacustris, Raphidascaris acus, Spinitectus inermis and Anguillicola crassus), cestodes (Bothriocephalus claviceps and Proteocephalus macrocephalus) and monogeneans (Pseudodactylogyrus sp.). The parasite fauna at the different locations is discussed with respect to the crustacean fauna present at these locations. The investigation shows that changes in the composition of the crustacean fauna, due to the anthropogenic breakdown of a biogeographic barrier, are reflected in the composition of the intestinal eel parasite fauna.     

Novel observations of midge and mosquito larval population dynamics in leaves of the northern pitcher plant,Sarracenia purpurea L.

The invertebrate communities in Sarracenia purpurea were characterized by surveying the contents of 474 leaves from six pitcher plant populations in the eastern United States. More than 8200 invertebrate specimens, both living and dead, were recovered. Midge and mosquito larvae comprised 7907 (96%) of the specimens, with a mean of 16.9 dipteran larvae per leaf. Although midge larvae were present at all collection sites, mosquito larvae were absent from two of the sites. In the latter sites, the number of midge larvae per leaf was greater. This report documents for the first time that there is no statistical difference between the average number of Diptera larvae per leaf for sites that contain both midge and mosquito larvae compared to sites that contain only midge larvae. It appears that pitcher plants maintain an average number of larvae per leaf based on a number of interacting factors which we do not fully understand. This investigation documents that in the absence of mosquito larvae, more midge larvae are found per leaf per leaf than would be predicted based on data from sites that contain both larval taxa.     

Effects of capacity on resource input and the aquatic metazoan community structure in phytotelmata

Aquatic metazoan communities in treeholes and bamboo stumps were studied on Tsushima Island, Japan, in March and June in relation to the habitat size and the resouce amount. The amount of leaf detritus increased with an increase in the capacity (volume) of the phytotelma. The input rate of leaves depended upon the opening area of the phytotelma. Twenty-one metazoan inhabitant taxa consisted of 17 dipteran saprophages, a helodid beetle larva, a nematoda, a naidid, and a predator,Toxorhynchites towadensis mosquito larva. Treeholes harbored 17 taxa and bamboo stumps 20; 16 taxa were common in both phytotelmata. The number of taxa and the biomass of metazoa per phytotelma was positively correlated with the capacity. The densities of dominant saprophages such as helodid, chironomid, andCulicoides larvae were positively correlated with the capacity of phytotelmata, and the variation in their abundance contributed much to the variation in the species composition in individual phytotelmata. With an increase in capacity, treeholes harbored more helodids andCulicoides, whereas bamboo stumps harbored more chironomids andDasyhelea. Thus, the amount of resource, species richness and biomass per phytotelma largely depended upon the capacity, and the difference in community structure between treeholes and bamboo stumps was attributable to the differential colonization patterns of different taxa.     

Das phylogenetische System der Tanaidacea und die Frage nach Alter and Herkunft der Crustaceenfauna des antarktischen Festlandsockels1,2

The phylogenetic system of the Tanaidacea and the question of age and origin of the crustacean fauna on the Antarctic shelf The final breakup of Gondwanaland during the Tertiary not only played an important role in establishing modern climates and oceanic currents but also had a tremendous influence on the composition of the Recent crustacean fauna. Analysis of the fossil record of the Tanaidacea shows that all Recent families had evolved before the Eocene. They all, therefore, had the chance to colonize the Antarctic shelf area. However, the tanaidacean fauna of this region is represented exclusively by phylogenetically young taxa. The species composition is atypical and does not correspond to those of other zoogeographic regions. Surprisingly, in the West Antarctic there occur some phylogenetic older taxa which are not recorded from the East Antarctic. In general, the species composition of the East Antarctic tanaidacean fauna is more like that of the deep sea while that of the West Antarctic is characterized by additional “littoral elements”. For the interpretation of recognized distribution patterns are most important geological events and the resulting effects on the changes in the world climates, e. g. it is commonly excepted that there is a continuous decrease of the surface water temperature since the paleocene. Deduced from foraminiferan data, it can be assumed that almost the entire Antarctic tanaidacean fauna was extinguished during the first dramatic drop of temperature. Cold-stenothermic eurybathic species then have colonized the Antarctic shelf. After the phase of maximal glaciation in the Pliozene the fauna of the West Antarctic was finally modified by Magellanian elements, which in some cases have to be accepted as phylogenetic old forms. Other available information on Crustacea, especially for Cirripedia, Ostracoda, Decapoda, and Isopoda support this interpretation. Therefore, it may be assumed that the Recent Antarctic crustacean fauna was established mainly about 38 m. y. ago. Practically no primitiv forms exist in this region, i. e. there are no relict species. On the contrary, we have to suggest that an important part of the fauna is represented by apomorphic species which have reached the Antarctic shelf from the deep sea. Polar emergence is a more likely hypothesis at the moment than tropical submergence. However, the final elucidation of this question can be given only after detailed phylogenetic analysis of the fauna of the adjacent deep sea basins.     

Mosquitoes and other aquatic insects in fallow field biotopes and rice paddy fields

Fallow field biotopes that develop from abandoned rice fields are man‐made wetlands that provide new habitats for various aquatic animals. Although consideration of such biotopes generally focuses on their positive aspects, this study evaluated the negative aspects of establishing fallow field biotopes with regard to mosquito breeding sites. To determine whether fallow field biotopes become breeding habitats for vector mosquitoes, we evaluated mosquito fauna in fallow field biotopes and adjacent rice fields. We found larvae of Anopheles lesteri, Anopheles sinensis and Culex tritaeniorhynchus (all: Diptera: Culicidae) in the biotopes. Although abundances of mosquito larvae in the biotopes and rice fields were statistically similar, mosquito abundances in rice fields increased dramatically in August when the water level reduced after the rainy season. The abundance and variety of the mosquitoes' natural predators were greater in biotopes than in rice fields because the former are a permanent and stable aquatic environment. A generalized linear mixed model showed a negative effect of predator diversity on mosquito larvae abundance in both habitats. Although fallow field biotopes become breeding habitats for vector mosquitoes, establishing biotopes from fallow fields in order to protect various aquatic animals, including mosquito insect predators, may help to control mosquito breeding.     

Food and feeding habits of the larvivorous fish Aplocheilus lineatus (Cuv. & Val.) in its natural habitat

Results are presented of a study of the food and feeding habits of Aplocheilus lineatus under natural conditions and the manner in which dietary preferences are influenced by the habitat/environment, seasons and stage of maturity of the fish is explained, based on data from montly random samples collected for a year. A qualitative assessment of the diet reveals that it is not confined to a varied range of aquatic fauna, but also encompasses allochthonous fauna. Quantitative and qualitative analyses of the diet indicate its feeding habit which does not alter with size or seasonal changes. The range of prey consumed does not differ radically, qualitatively, as a function of size, but quantitatively exhibits five levels of discrimination and differential exploitation related mainly to prey size. Seasonal fluctuations in feeding are more qualitative than quantitative and seem dependent on the occurrence of food organisms. The lack of correlation between breeding and feeding is linked to extent of the development of the gonad in the body cavity. In conclusion, the potential of the fish as an effective biological control agent of mosquito larvae is indicated by the fact that dipteran larvae are a preferred item of its diet in all size groups.