Specific detection of the floodwater mosquitoes Aedes sticticus and Aedes vexans DNA in predatory diving beetles

Floodwater mosquitoes (Diptera: Culicidae) are associated with periodically flooded wet meadows, marshes, and swamps in floodplains of major rivers worldwide, and their larvae are abundant in the shallow parts of flooded areas. The nuisance caused by the blood‐seeking adult female mosquitoes motivates mosquito control. Larviciding with Bacillus thuringiensis israelensis is considered the most environmentally safe method. However, some concern has been raised whether aquatic predatory insects could be indirectly affected by this reduction in a potential vital prey. Top predators in the temporary wetlands in the River Dalälven floodplains are diving beetles (Coleoptera: Dytiscidae), and Aedes sticticus and Ae. vexans are the target species for mosquito control. For detailed studies on this aquatic predator–prey system, we developed a polymerase chain reaction (PCR) assay for detection of mosquito DNA in the guts of medium‐sized diving beetles. Primers were designed for amplifying short mitochondrial DNA fragments of the cytochrome C oxidase subunit I (COI) gene in Ae. sticticus and Ae. vexans, respectively. Primer specificity was confirmed and half‐life detectability of Ae. sticticus DNA in diving beetle guts was derived from a feeding and digestion experiment. The Ae. sticticus DNA within diving beetle guts was detected up to 12 h postfeeding, and half‐life detectability was estimated to 5.6 h. In addition, field caught diving beetles were screened for Ae. sticticus and Ae. vexans DNA and in 14% of the diving beetles one or both mosquito species were detected, showing that these mosquito species are utilized as food by the diving beetles.     

Diving beetles (Dytiscidae) as predators of mosquito larvae (Culicidae) in field experiments and in laboratory tests of prey preference

Field experiments were performed in artificial ponds to evaluate how the density of predatory diving beetles (Dytiscidae) would affect the population levels of mosquito larvae (Culicidae). Mosquitoes colonizing the ponds were predominantly species of the genus Culex. In 2000, most of the dytiscids colonizing the ponds were small (Hydroporus spp.), and these predators had no impact on the size of larval mosquito populations, not even in ponds with added dytiscids. In 2001, larger beetles (Ilybius, Rhantus, and Agabus spp.) were more common, and there were significantly fewer mosquito larvae in ponds with the highest numbers of dytiscids. There was a negative correlation between numbers of diving beetles in the ponds and the mean body length of mosquito larvae. In neither year could dytiscid densities be maintained above a certain level owing to emigration. In laboratory tests, there were marked differences between three common dytiscid species in regard to preferences for Daphnia and Culex species as prey: Colymbetes paykulli Erichson chose mosquito larvae more often, whereas both Ilybius ater (De Geer) and I. fuliginosus (Fabricius) preferred Daphnia spp. All of the tested dytiscids consumed large numbers of prey. Since some dytiscid species can efficiently decrease populations of mosquito larvae, they are probably important in the natural control of these dipterans.     

Body size, rarity, and phylogenetic community structure: insights from diving beetle assemblages of Alberta

Although it is implicit that interactions between species depend on their traits, studies on the probability of finding related species in a community are in their infancy. Community composition and species richness of predaceous diving beetles (Dytiscidae: Coleoptera) have been used as indicators of freshwater ecosystem function yet no incorporation of phylogenetic relationships of coexisting dytiscids has been attempted to date. Improved knowledge of phylogenetic relationships and phylogenetic community structure analysis methods may provide additional insight into the relationships between community composition and species richness, thus impacting our interpretation of aquatic indicator species metrics. Here, we use museum records of dytiscid beetles in 53 lakes of Alberta, Canada to: (1) compile a supertree of dytiscid beetles that live in the province, (2) examine whether coexisting dytiscids tend to be more or less related than expected by chance, and (3) examine whether phylogenetic structuring depends on species richness or mean size of coexisting species. We find that, although the majority of dytiscid assemblages exhibited phylogenetic clustering, the extent to which this occurred depended on the mean size of dytiscids. We discuss the potential mechanisms and implications of the observed patterns in phylogenetic clustering, along with data that would further improve our understanding of community dynamics in dytiscid beetles.     

Paroster extraordinarius sp. nov., a new groundwater diving beetle from the Flinders Ranges, with notes on other diving beetles from gravels in South Australia (Coleoptera: Dytiscidae)

The first groundwater (stygobitic) diving beetle is reported from South Australia. Paroster extraordinarius sp. nov. (Dytiscidae: Hydroporini) is described and figured. Its morphology and mitochondrial DNA sequences place it in the hydroporine genus Paroster Sharp. Phylogenetic analysis shows that the new species is imbedded in a clade of stygobitic species from the Yilgarn area of Western Australia. The evolution of this species is discussed and compared with observations on the behaviour and distribution of other dytiscid beetles found in subterranean habitats in South Australia.     

Field observation of predation on a horsehair worm (Gordioida: Chordodidae) by a diving beetle larva Cybister brevis Aubé (Coleoptera: Dytiscidae)

Diving beetles (Coleoptera: Dytiscidae) are carnivorous in both the larval and adult stages; larvae are exclusively predatory, whereas adults also scavenge for food. They are known to prey on zooplankton, insects, gastropods, fish, amphibians and reptiles. However, there have been no previous reports detailing direct predation on adult Gordioida by Dytiscidae in the field. This study represents the first observation of a diving beetle larva, Cybister brevis Aubé (Coleoptera: Dytiscidae), predating on an adult horsehair worm (Gordioida: Chordodidae). This might be the first report of predation on horsehair worms by insects.     

Do invertebrate communities in floodplains change predictably along a river's length?

1. Invertebrate assemblages were described for nine floodplain sites located on a longitudinal gradient of river discharge in the Altamaha River catchment. The Altamaha River and its tributaries constitute one of the few remaining ‘unregulated’ catchments in the southeastern U.S. We predicted that, as the character of lateral flood pulses into backwater swamps changed along the discharge gradient, so would the structure of invertebrate communities. We also examined the relationship between invertebrate assemblages and physicochemical factors (degree of floodplain inundation, pH, conductivity and nutrient concentrations). 2. Cluster analyses of both invertebrate abundance and biomass separated the nine sites into three groups corresponding to their positions in the catchment (upper, mid‐ and lower reach clusters). Non‐metric multidimensional scaling ordinations further corroborated the groupings (with combined axis scores of 92% and 73% for abundance and biomass, respectively) and showed significant correlations with degree of inundation and conductivity (abundance), and conductivity, nitrate and phosphate concentrations (biomass). 3. Floodplains in the upper reaches were dominated by terrestrial taxa, such as earthworms, oribatid mites, collembolans and assorted terrestrial fly larvae, and some rapidly developing aquatics (harpacticoid crustaceans and mosquitoes). In the mid‐reach, the dominant taxa were longer lived aquatic organisms such as mayflies and aquatic oligochaetes, although some terrestrial organisms (elaterid beetles and mites) were still common. Invertebrate families dependent on water flow, such as riffle beetles and some mayflies, were common only in mid‐reach floodplain sites. Lower reaches were dominated by lentic aquatic taxa such as dytiscid beetles and asellid isopods, which commonly persist in wetlands after they dry. 4. Our study indicates that invertebrate community structure varies predictably among floodplains in the Altamaha catchment, with headwater habitats being dominated by terrestrial and rapidly‐developing aquatic invertebrates, mid‐reaches characterised by an influx of invertebrates from the river and lower reaches being dominated by wetland taxa with desiccation‐resistant stages. This spatial variability should be considered when applying the Flood Pulse Concept.     

Flood pulses drive the temporal dynamics of assemblages of aquatic insects (Heteroptera and Coleoptera) in a temperate floodplain

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How important are aquatic predators to mosquito larval populations in natural wetlands? A case study from Carolina bays in Georgia

Predation is believed to be an important natural control on larval mosquito populations. However, empirical evidence for predator impacts is lacking, especially from natural wetlands (swamps and marshes). Over a 2-year period, we sampled larval mosquito populations and naturally co-occurring predator assemblages (aquatic invertebrates, fishes) from ten depressional wetlands (Carolina bays) located on a wildlife management area in east central Georgia. We collected a diversity of mosquito larvae and predators (odonates, bugs, beetles, flies, and fishes) from the wetlands, with predator numbers substantially exceeding mosquito larval numbers. However, using a community ecology approach with multivariate ordination and correlation techniques, we found no compelling evidence that these predators were controlling mosquito larval distributions (i.e. significant negative statistical associations were not detected). Those mosquitoes that successfully breed in Carolina bay wetlands (Culiseta melanura, Coquillettidia perturbans, Anopheles crucians) appear well adapted to co-exist with a plethora of naturally occurring predators.     

Knitting patterns of biodiversity,range size and body size in aquatic beetle faunas: significant relationships but slightly divergent drivers

1. Ecogeographical rules refer to recurring patterns in nature, including the latitudinal diversity gradient (LDG), Rapoport's rule and Bergmann's rule, amongst others. In the present study, the existence of these rules was examined for diving beetles (Coleoptera: Dytiscidae), a family of aquatic predatory beetles. 2. Assemblage‐level data were analysed for diving beetles, focusing on species richness, local contribution to beta diversity (LCBD), mean range size and mean body size across the biogeographical provinces of Northern Europe. First, each of these variables was correlated with latitude, and then variation in each variable was modelled using actual environmental variables in boosted regression tree analysis. 3. Species richness was found to decrease with latitude, LCBD increased with latitude, mean range size did not show a significant relationship with latitude, and mean body size decreased with latitude. The latter finding was in contrast to Bergmann's rule. The actual environmental variables best predicting variation in these four response variables varied among the models, although they generally included temperature‐related and land use variables as the most influential ones. 4. The results obtained in the present study suggest that diving beetles conformed to the LDG, did not follow Rapoport's rule, and showed a reversed latitudinal gradient in the context of Bergmann's rule. In addition, species‐poor provinces harboured ecologically most unique faunas, suggesting that species richness and LCBD are complementary measures of biodiversity. 5. Even though general support was not found for most of the ecogeographical rules examined, the findings of the present study are interesting because they suggest that aquatic ectothermic invertebrates may show patterns different from those originally described for terrestrial endothermic vertebrates.     

Selective predation by larval Agabus (Coleoptera: Dytiscidae) on mosquitoes: support for conservation-based mosquito suppression in constructed wetlands

1. Wetland insect predators can structure aquatic prey communities via selective predation, but receive considerably less attention than vertebrate predators. We conducted laboratory experiments to test selective predation by two species of larval dytiscid beetles ( Agabus ; Coleoptera: Dytiscidae) and the potential contribution of these beetles to suppression of mosquito populations in constructed wetlands.
2.  Agabus consumed copepods, ostracods and mosquito larvae in no-choice tests. When offered a choice, 76% of all prey consumed were mosquito larvae, indicating selective predation. Subsequent experiments revealed this preference was due to ease of capture of mosquito larvae over alternative prey.
3. Cannibalism and intraguild predation were common within and between species of Agabus , which may reduce the overall impact of the observed selective predation.
4.  Agabus larvae selectively preyed on mosquito larvae over alternative prey, which is not characteristic of some fish used as biological control agents for mosquitoes. Predator exclusion or similar experiments in the field could document how these results translate into a natural setting.
5. The findings of this study suggest developing mosquito suppression strategies focused on conservation of native wetland predators. These strategies are preferable to introducing non-native generalist predators, or applying pesticides.     

Predatory Lady Beetles (Coleoptera,Coccinellidae) in Cereal Agrocenoses in the Northern Forest-Steppe of West Siberia and the Influence of Agrotechnical Methods on Them

Predatory lady beetles (Coccinellidae) form one of the prevalent and effective groups of entomophages in the forest-steppe zone of West Siberia. Among 17 species of predatory lady beetles recorded in cereal agrocenoses and on bird cherry trees, Propylea quatuordecimpunctata, Coccinella septempunctata, Hippodamia tredecimpunctata, H. variegata, and H. arctica are predominant. This paper presents data on the species composition and ecological features of lady beetles in agrocenoses of winter rye, spring wheat, and oats as well as on the impact of agrotechnical methods (the main treatment of soil, application of chemicals, and forecrops) and cultivation technology on the abundance of lady beetles.     

Abundance and species richness patterns of diving beetles (Coleoptera, Dytiscidae) from exposed and protected sites in 98 northern Swedish lakes

Forty species of predaceous diving beetles (Coleoptera, Dytiscidae) were collected in sweepnet samples from 98 boreal lakes in northern Sweden. Samples from protected sites with vegetation had significantly more specimens and species than those from exposed sites without vegetation in the same lakes. No geographically based differences, e.g. latitudinal or in distance from the coast, were found. These gradients were 200 and 150 km long, respectively. Species' distribution in terms of occurence at number of sites was positively correlated with the mean abundance of the species. The relationship between species' abundance and body length was characterized by the lack of large, abundant species. Partial least square regressions on dytiscid abundance and species richness showed low predictive power of lake area, altitude and water chemistry. The seven environmental variables used explained at best 15.3 and 24.4% of the total variance in abundance and species richness, respectively. The results are compared to activity trap catches of dystiscids in lakes in an adjacent region. A majority of the species occured in both materials. However, species occuring in high proportion in one of the materials, were rare in the other material. The mean body length of the species caught more efficiently with traps was not larger than that of those overpresented in net sampling. Based on this study and the available literature data, the regional species pool of boreal lake dytiscids is estimated to 30–40 species. It is still an open question if lake assemblages are markedly poorer than those found in the development of vegetation, whereas the impact of water chemistry is small.     

The comparative biology of diving in two genera of European Dytiscidae (Coleoptera)

Surfacing behaviour is fundamental in the ecology of aquatic air-breathing organisms; however, it is only in vertebrates that the evolutionary ecology of diving has been well characterized. Here, we explore the diving behaviour of dytiscid beetles, a key group of surface-exchanging freshwater invertebrates, by comparing the dive responses of 25 taxa (Deronectes and Ilybius spp.) acclimated at two temperatures. The allometric slopes of dive responses in these dytiscids appear similar to those of vertebrate ectotherms, supporting the notion that metabolic mode shapes the evolution of diving performance. In both genera, beetles spend more time submerged than on the surface, and surface time does not vary with the temperature of acclimation. However, presumably in order to meet increased oxygen demand at higher temperatures, Deronectes species increase surfacing frequency, whereas Ilybius species decrease dive time, an example of 'multiple solutions.' Finally, widespread northern species appear to possess higher diving performances than their geographically restricted southern relatives, something which may have contributed to their range expansion ability.     

Variation in prey-specific consumption rates and patterns of field co-occurrence for two larval predaceous diving beetles

Freshwater predatory insects can exert strong effects on prey, although how multiple similar predators may coexist is not well understood. Larval predaceous diving beetles are often numerically and taxonomically abundant predators in lentic systems, but the proximate mechanisms that explain their high abundance remain unknown. Field surveys were conducted twice in June in ponds in Alberta, Canada to assess the associations between larvae of two genera (Graphoderus, Rhantus), their spatial locations, and correlations with potential prey. Both larvae were common and positively correlated within wetlands although neither varied with pond depth nor distance from edge. Laboratory trials indicated that Graphoderus consumed more prey (corixids) at the surface, whereas Rhantus killed benthic prey (chironomids) and corixids at an equal rate; damselflies were the least consumed prey. Predation also varied with depth, with both larvae feeding at higher rates in the shallowest environments compared to Graphoderus at an intermediate depth. Predator–prey correlations from ponds were mostly congruent with predation trials; Graphoderus was positively correlated with corixids, Rhantus was positively correlated with corixids and chironomids; beetles were uncorrelated with damselflies. Reliance on different prey in different microhabitats may be an important mechanism for the maintenance of high abundance of dytiscid larvae.     

Sexual dimorphism and sexual conflict in the diving beetle Agabus uliginosus (L.) (Coleoptera: Dytiscidae)

Sexual conflict can drive intersexual arms races, with female resistance and male persistence traits coevolving antagonistically. Such arms races are well documented in some diving beetles, although the extent of sexual conflict in this family remains unclear. The European dytiscid Agabus uliginosus has a strikingly dimorphic female; individuals from most regions are smooth and male‐like, whereas those from some populations have a strongly roughened dorsum, a trait that has attracted the name dispar. We demonstrate that rough and smooth females differ consistently in the development of dorsal surface microreticulation, and that these females are associated with males that differ in the development of their persistence traits. These findings extend the occurrence of pre‐insemination sexual conflict and associated intrasexual dimorphism in Dytiscidae, and suggest that such mating systems are relatively widespread in these beetles.     

Assemblages of dytiscid predators and culicid prey in relation to environmental factors in natural and clear-cut boreal swamp forest pools

Assemblages of diving beetles (Dytiscidae) and mosquito immatures (Culicidae) were studied during 1987–1988 in 40 small, more or less temporary, snowmelt pools in spruce swamp forest and clearings at the Arctic Circle in Sweden. Larger pools were warmer than smaller ones, and clearing pools were warmer than forest pools. Temperature differences between pools remained high until late July. Twenty-one dytiscid species, representing three guilds, occurred in the pools, and individual pools had 1–13 species. Ten species occurred in both habitats. A few stenotopic species of boreal swamp forests had in clearing pools apparently been replaced by some species with a preference for more productive, often man-made habitats. Six Aedes species were collected in the clearing pools. Five of these were found in the forest pools, of which three had no mosquito larvae. Dytiscid assemblages in both habitats and culicid assemblages in clearing pools showed strong nested patterns.Abundance and species richness of both culicids and dytiscids were higher in clearing than in forest pools with an area >2 m² after that the effects of pool area had been accounted for (MANCOVA). In both habitats, abundance and species richness of both culicids and dytiscids were strongly and positively correlated with a linear combination of pool area, depth and temperature (Canonical Correlation). Increasing drought frequency of pools had a negative, less significant effect on the biota. In the clearing, the abiotic correlations with abundance were somewhat weakened chiefly by the relatively low abundance values from the largest pool.Distribution and mean abundance of individual dytiscid species were positively related in the clearing pools. Flying dytiscids were trapped in the larger (1.6 m²), but not in the smaller (0.07 m²) artificial pools, and the immigration rate was markedly higher on clearings than in forest. Dug pools were colonized faster on clearings than in forest. Even the flightless Hydroporus melanarius colonized dug pools during the first year.     

Effects of a top invertebrate predator (<Emphasis Type="Italic">Dytiscus alaskanus</Emphasis>; Coleoptera: Dytiscidae) on fishless pond ecosystems

We investigated the predatory effects of Dytiscus alaskanus, a large predaceous diving beetle, on the biomass, species composition and diversity of fishless pond communities. The effects were tested using presence and absence treatments of D. alaskanus in 24 mesocosms distributed among six ponds. We sampled phytoplankton, zooplankton and macroinvertebrates every two weeks for a six week period. Periphyton was sampled from the mesocosm walls on the final day. Total macroinvertebrate biomass decreased in the presence of dytiscids while species richness was not affected. Macroinvertebrate predators, snails and Gammarus lacustris decreased in the dytiscid treatments. Laboratory feeding experiments confirmed feeding preferences consistent with the mesocosm results. Periphyton biomass was six times greater in the dytiscid enclosures, concomitant with the decreased grazing by gastropods and other invertebrate primary consumers indicating a benthic trophic cascade. Top–down effects of dytiscids on other predatory invertebrates led to increased total zooplankton biomass, largely due to increased abundances of large and small cladocerans. Zooplankton species richness increased in the dytiscid enclosures. Inconsistent with trophic cascade theory, phytoplankton did not respond to top–down effects of D. alaskanus within the study period. Overall, the results show D. alaskanus predation caused trophic effects via two distinct food chains, a dytiscid–snail–periphyton trophic cascade, and a dytiscid–predatory macroinvertebrates–zooplankton partial trophic cascade.     

Vegetation,invertebrate, and fish community response to past and current flow regulation in floodplains of the Savannah River,Southeastern USA

In 2005 and 2006, the United States Army Corps of Engineers released experimental flows to mimic natural spring flooding on the highly regulated lower Savannah River in the Southeastern US. We used vegetation, invertebrate, and fish communities to assess how past regulation and current experimental releases were affecting the ecological conditions on floodplains. The nearby Altamaha River, of similar size but retaining near-natural spring pulses, served as a reference. We did not find that past flow regulation of the Savannah River had significantly altered floodplain forest structure. However, numbers of tree seedlings in bottomland hardwood forests were higher during a year with an artificial pulse than one without. Analyses of invertebrate and fish communities suggested some limited differences in floodplain community structure between rivers, with differences being most pronounced for predaceous Dytiscidae beetles and Esox spp. fishes. Artificial re-creation of small spring flood pulses down the Savannah River in 2005 and 2006 elicited some responses from fish and invertebrates, but did not shift species assemblages towards those occurring on Altamaha River floodplains.     

Competitive displacement alters top-down effects on carbon dioxide concentrations in a freshwater ecosystem

Climate change and invasive species have the potential to alter species diversity, creating novel species interactions. Interspecific competition and facilitation between predators may either enhance or dampen trophic cascades, ultimately influencing total predator effects on communities and biogeochemical cycling of ecosystems. However, previous studies have only investigated the effects of a single predator species on CO₂ flux of aquatic ecosystems. In this study, we measured and compared the individual and joint effects of predatory damselfly larvae and diving beetles on total prey biomass, leaf litter processing, and dissolved CO₂ concentrations of experimental bromeliad ecosystems. Damselfly larvae created strong trophic cascades that reduced CO₂ concentrations by ~46 % relative to no-predator treatments. Conversely, the effects of diving beetles on prey biomass, leaf litter processing, and dissolved CO₂ were not statistically different to no-predator treatments. Relative to multiplicative null models, the presence of damselfly larvae and diving beetles together resulted in antagonistic relations that eliminated trophic cascades and top-down influences on CO₂ concentrations. Furthermore, we showed that the antagonistic interactions between predators occurred due to a tactile response that culminated in competitive displacement of damselfly larvae. Our results demonstrate that predator identity and predator–predator interactions can influence CO₂ concentrations of an aquatic ecosystem. We suggest that predator effects on CO₂ fluxes may depend on the particular predator species removed or added to the ecosystem and their interactions with other predators.     

<Emphasis Type="Italic">Genista</Emphasis> dwarf shrubs as key structures for a Mediterranean grasshopper species on alluvial gravel banks

Natural floodplains belong to the most species-rich ecosystems worldwide. However, over the last decades there has been a strong decrease in the extent of natural floodplains. As a consequence, the biodiversity of these ecosystems has experienced a dramatic decline. In this study, we investigated the habitat and food preferences of the grasshopper species Chorthippus binotatus on gravel banks of a nearly natural river system in the Spanish Pyrenees. The studied plots on the alluvial gravel banks in the Spanish Pyrenees were characterised by strong differences in habitat structure. However, C. binotatus only occurred in sparsely-vegetated sub-Mediterranean dry grasslands. The abundance of the grasshopper species was also strongly related to habitat structure and cover of the main food source and dominant plant species of these open grasslands, the dwarf shrub Genista scorpius. Concerning habitat structure, the grasshopper species preferred habitats with sparse and low-growing vegetation with a high cover of bare ground and gravel/stones. C. binotatus occupies a very narrow ecological niche within the studied floodplain. It requires sparsely-vegetated gravel banks that ensure sufficient oviposition sites and a favourable ambient temperature for optimal development. G. scorpius dwarf shrubs have to be considered as multi-functional key elements in the habitats of C. binotatus. They offer high-quality food, shelter against predators and allow thermoregulation in a hot and dry Mediterranean environment. For the conservation of C. binotatus, we recommend maintaining and restoring both natural floodplain dynamics as well as traditional grazing systems.