Bacterial microbiota assemblage in Aedes albopictus mosquitoes and its impacts on larval development

Interactions between bacterial microbiota and mosquitoes play an important role in mosquitoes’ capacity to transmit pathogens. However, microbiota assemblages within mosquitoes and the impact of microbiota in environments on mosquito development and survival remain unclear. This study examined microbiota assemblages and the effects of aquatic environment microbiota on the larval development of the Aedes albopictus mosquito, an important dengue virus vector. Life table studies have found that reducing bacterial load in natural aquatic habitats through water filtering and treatment with antibiotics significantly reduced the larva‐to‐adult emergence rate. This finding was consistent in two types of larval habitats examined—discarded tires and flowerpots, suggesting that bacteria play a crucial role in larval development. Pyrosequencing of the bacterial 16S rRNA gene was used to determine the diversity of bacterial communities in larval habitats and the resulting numbers of mosquitoes under both laboratory and field conditions. The microbiota profiling identified common shared bacteria among samples from different years; further studies are needed to determine whether these bacteria represent a core microbiota. The highest microbiota diversity was found in aquatic habitats, followed by mosquito larvae, and the lowest in adult mosquitoes. Mosquito larvae ingested their bacterial microbiota and nutrients from aquatic habitats of high microbiota diversity. Taken together, the results support the observation that Ae. albopictus larvae are able to utilize diverse bacteria from aquatic habitats and that live bacteria from aquatic habitats play an important role in larval mosquito development and survival. These findings provide new insights into bacteria's role in mosquito larval ecology.     

Larval development of Culex quinquefasciatus in water with low to moderate

Population growth and urbanization have increased the potential habitats, and consequently the abundance of Culex quinquefasciatus, the southern house mosquito, a vector of West Nile Virus in urban areas. Water quality is critical in larval habitat distribution and in providing microbial food resources for larvae. A mesocosm experiment was designed to demonstrate which specific components of water chemistry are conducive to larval Culex mosquitoes. Dose–response relationships between larval development and NO₃, NH₄, and PO₄ concentrations in stream water were developed through this experiment to describe the isolated effects of each nutrient on pre‐adult development. The emergence pattern of Culex mosquitoes was found to be strongly related to certain nutrients, and results showed that breeding sites with higher PO₄ or NO₃ concentrations had higher larval survival rates. High NO₃ concentrations favor the development of male mosquitoes and suppress the development of female mosquitoes, but those adult females that do emerge develop faster in containers with high NO₃ levels compared to the reference group. The addition of PO₄ in the absence of nitrogen sources to the larval habitat slowed larval development, however, it took fewer days for larvae to reach the pupal stage in containers with combinations of NO₃ and PO₄ or NH₄ and PO₄ nutrients. Results from this study may bolster efforts to control WNV in urban landscapes by exploring water quality conditions of Culex larval habitats that produce adult mosquitoes.     

Keystone nonconsumptive effects within a diverse predator community

The number of prey killed by diverse predator communities is determined by complementarity and interference among predators, and by traits of particular predator species. However, it is less clear how predators' nonconsumptive effects (NCEs) scale with increasing predator biodiversity. We examined NCEs exerted on Culex mosquitoes by a diverse community of aquatic predators. In the field, mosquito larvae co‐occurred with differing densities and species compositions of mesopredator insects; top predator dragonfly naiads were present in roughly half of surveyed water bodies. We reproduced these predator community features in artificial ponds, exposing mosquito larvae to predator cues and measuring resulting effects on mosquito traits throughout development. Nonconsumptive effects of various combinations of mesopredator species reduced the survival of mosquito larvae to pupation, and reduced the size and longevity of adult mosquitoes that later emerged from the water. Intriguingly, adding single dragonfly naiads to ponds restored survivorship of larval mosquitoes to levels seen in the absence of predators, and further decreased adult mosquito longevity compared with mosquitoes emerging from mesopredator treatments. Behavioral observations revealed that mosquito larvae regularly deployed “diving” escape behavior in the presence of the mesopredators, but not when a dragonfly naiad was also present. This suggests that dragonflies may have relaxed NCEs of the mesopredators by causing mosquitoes to abandon energetically costly diving. Our study demonstrates that adding one individual of a functionally unique species can substantially alter community‐wide NCEs of predators on prey. For pathogen vectors like mosquitoes, this could in turn influence disease dynamics.     

Relationships between predatory aquatic insects and mosquito larvae in residential areas in northern Thailand

In order to elucidate the poorly understood relationships between mosquito larvae and their predatory aquatic insects in urban and suburban areas of tropical Southeast Asia, where vector‐borne diseases are prevalent, aquatic insects were sampled from 14 aquatic habitats in residential areas of Chiang Mai, northern Thailand, during the rainy season (July to November) in 2016. Correlations among biological variables, densities of major predatory aquatic insect groups (i.e., Odonata, Coleoptera, and Hemiptera: OCH group) in wetlands and artificial lentic habitats, and the density of mosquito larvae were analyzed. Among the sampled mosquito larvae, Culex spp. were the most abundant, and both OCH density and water quality were major determinants of Culex spp. density (r_s = ?0.302 and ?0.396, respectively). Logistic regression analyses indicated that the probability of Culex spp. occurrence was significantly and negatively correlated with OCH density. Furthermore, high macrophyte abundance was associated with higher predator density, potentially reducing mosquito density. Hemipteran predators were most negatively correlated with Culex spp. density, regardless of whether macrophyte abundance was high or low (r_s = ?0.547 and ?0.533, respectively). Therefore, hemipteran predators were the most important aquatic insect predators in the urban and suburban residential areas of Chiang Mai, Thailand, and OCH species, such as the hemipteran Micronecta scutellaris, could be used as biological control agents against mosquitoes in the region.     

Effect of Leaf Type and Pesticide Exposure on Abundance of Bacterial Taxa in Mosquito Larval Habitats

Lentic freshwater systems including those inhabited by aquatic stages of mosquitoes derive most of their carbon inputs from terrestrial organic matter mainly leaf litter. The leaf litter is colonized by microbial communities that provide the resource base for mosquito larvae. While the microbial biomass associated with different leaf species in container aquatic habitats is well documented, the taxonomic composition of these microbes and their response to common environmental stressors is poorly understood. We used indoor aquatic microcosms to determine the abundances of major taxonomic groups of bacteria in leaf litters from seven plant species and their responses to low concentrations of four pesticides with different modes of action on the target organisms; permethrin, malathion, atrazine and glyphosate. We tested the hypotheses that leaf species support different quantities of major taxonomic groups of bacteria and that exposure to pesticides at environmentally relevant concentrations alters bacterial abundance and community structure in mosquito larval habitats. We found support for both hypotheses suggesting that leaf litter identity and chemical contamination may alter the quality and quantity of mosquito food base (microbial communities) in larval habitats. The effect of pesticides on microbial communities varied significantly among leaf types, suggesting that the impact of pesticides on natural microbial communities may be highly complex and difficult to predict. Collectively, these findings demonstrate the potential for detritus composition within mosquito larval habitats and exposure to pesticides to influence the quality of mosquito larval habitats.     

Effects of a larval mosquito biopesticide and Culex larvae on a freshwater nanophytoplankton (Selenastrum capricornatum) under axenic conditions

The effects of microbial biopesticides used for mosquito control on autotrophic microorganisms such as nanophytoplankton are equivocal. We examined impacts of mosquito biopesticides and mosquito larvae on primary producers in two independent experiments. In the first experiment, we examined the effects of a commonly used microbial biopesticide formulation (VectoMax^® CG) on a unicellular microalga, Selenastrum capricornatum Printz, under axenic laboratory conditions. The biopesticide treatments included two concentrations (0.008 and 0.016 g liter^?1) of VectoMax^® CG and two controls (one untreated and another with autoclaved 0.016 g VectoMax^® CG liter^?1) in replicated axenic experimental microcosms. Spectrophotometric analysis of chlorophyll a (proxy for algal biomass) and direct enumeration of algal cells following the treatments revealed no significant effects of the microbial biopesticide on algal population growth during the four‐week study. In the second experiment, we tested the effects of different densities of Culex larvae on the population of S. capricornatum. Effects of mosquito larvae feeding on S. capricornatum were significant with a curvilinear relationship between larval density and algal abundance in the water column. Together, these studies demonstrated a lack of direct cytological/toxicological effects of Bacillus‐based microbial pesticides on freshwater primary production and support the hypothesis that the reduction in algal primary production previously reported when Bti products were applied to aquatic environments was likely independent of the Bacillus‐based larvicidal toxins. Instead, it was likely mediated by microbial interactions in the water column and the trophic cascade effects that resulted from the removal of larval mosquitoes. These studies suggest that mosquito larvae independent of pesticide application can influence primary production. Our method of evaluating biopesticides against small photoautotrophs can be very useful for studying the unintended effects on autotrophic microorganisms of other pesticides, including herbicides and pesticides applied to aquatic environments.     

Ecology of planktonic heterotrophic flagellates. A review.

In aquatic environments heterotrophic flagellates are an important component within the microbial loop and the food web, owing to their involvement in the energy transfer and flux and as an intermediate link between bacteria and primary producers, and greater organisms, such as other protists and metazoan consumers. In the microbial loop heterotrophic flagellates highly contribute to fast biomass and nutrient recycling and to the production in aquatic environments. In fact, these protists consume efficiently viruses, bacteria, cyanobacteria and picophytoplankton, and are grazed mainly by other protists, rotifers and small crustaceans. In this paper the knowledge about these unicellular organisms is reviewed, taking into particular account their ecological relationships and trophic role within the plankton community of marine and freshwater environments.     

Microbial larvicides for mosquito control: Impact of long lasting formulations of Bacillus thuringiensis var. israelensis and Bacillus sphaericus on non‐target organisms in western Kenya highlands

The microbial larvicides Bacillus thuringiensis var. israelensis and Bacillus sphaericus have been used extensively for mosquito control and have been found to be effective and safe to non‐target organisms cohabiting with mosquito larvae. Recently developed long lasting microbial larvicides (LLML), although evading the previous challenge of short duration of activity, increase the risk of persistence of toxins in the treated larval habitats. This study monitored the impact of LLML FourStar^® and LL3 on non‐target organisms cohabiting with mosquito larvae in an operational study to control malaria vectors in western Kenya highlands. A total of 300 larval habitats were selected in three highland villages. The habitats were first monitored for 5 weeks to collect baseline data on non‐target organisms cohabiting with mosquito larvae and then randomized into two treatment arms (respective FourStar^® and LL3) and one control arm. Non‐target organisms were sampled weekly for 5 months after treatment to assess the impact of LLML intervention. Before treatment, the mean density of all non‐target organisms combined in the control, LL3 and FourStar^® treated habitats was 1.42, 1.39 and 1.49 individuals per habitat per sampling occasion, respectively. Following treatment, this density remained fairly unchanged for 21 weeks at which time it was 1.82, 2.11, and 2.05 for the respective control, LL3 and FourStar^® treated habitats. Statistical analysis revealed that LL3 and FourStar^® did not significantly alter abundance, richness or diversity of the 11 taxa studied, when comparing the intervention and control larval habitats. However, both FourStar^® and LL3 significantly reduced the density of malaria vectors. In conclusion, one round of label rate application of FourStar^® or LL3 in natural larval habitats did not alter richness, abundance or diversity of the monitored aquatic non‐target organisms cohabiting with mosquito larvae to an ecologically significant level.     

Effects of flash flooding on mosquito and community dynamics in experimental pools

Pulsed disturbances of larval mosquito sites are likely to have a direct negative effect on mosquitoes but may also have indirect effects due to the alteration of community structure. These altered communities may become attractive to gravid mosquitoes searching for oviposition sites when the disturbances decrease the abundance of mosquito antagonists such as competitors, which often results in an increase in mosquito food resources. However, flash flood disturbances in intermittent riverbeds can also remove mosquito food resources such as algae, so that the net effect of flash floods could be either to increase or decrease mosquito abundance. We conducted an outdoor mesocosm experiment to assess the effects of flash floods on mosquito oviposition habitat selection and larval abundance during the post‐disturbance period of community recovery. Mesocosms were artificially flooded. Mosquito oviposition, immature abundance, invertebrate species diversity, chlorophyll a, and abiotic parameters were monitored. Our results showed that the flash flood negatively affected phytoplankton and zooplankton, leading to a decrease of mosquito oviposition in flooded mesocosms compared to non‐flooded mesocosms. More broadly, this study indicates how disturbances influence mosquito oviposition habitat selection due to the loss of food resources in ephemeral pools, and it highlights the importance of considering the effects of disturbances in management, habitat restoration, and biodiversity conservation in temporary aquatic habitats.     

The roles of history: age and prior exploitation in aquatic container habitats have immediate and carry‐over effects on mosquito life history

1. Per‐capita resource availability in aquatic habitats is influenced directly by consumer density via resource competition and indirectly via delayed resource competition when temporally non‐overlapping cohorts of larvae exploit the same resources. In detritus‐based systems, resources are likely to be influenced by the age of the aquatic habitat, as detritus changes in quality over time and may be replenished by new inputs. 2. For aquatic insects that exploit detritus‐based habitats, feeding conditions experienced during immature stages can influence fitness directly via effects on development and survivorship, but also indirectly by influencing adult traits such as fecundity and longevity. 3. Larval habitat age and prior resource exploitation were manipulated in a field experiment using the container mosquito Aedes triseriatus. 4. It was found that A. triseriatus from older habitats had greater larval survival, faster development and greater adult longevity. Exploitation of larval habitats by a prior cohort of larvae had a significant negative effect on subsequent cohorts of larvae by delaying development. 5. It is suggested that extended conditioning of detritus probably resulted in conversion of recalcitrant resources to more available forms which improved the quality of the habitat. 6. In a parallel study, evidence was found of carry‐over effects of habitat age and prior exploitation on adult longevity for A. triseriatus and Aedes japonicus collected from unmanipulated aquatic habitats. 7. These results indicate the importance of detritus dynamics and the discontinuous nature of resource competition in these mosquito‐dominated aquatic systems.     

Fluxes of terrestrial and aquatic carbon by emergent mosquitoes: a test of controls and implications for cross-ecosystem linkages

Adult aquatic insects are a common resource for many terrestrial predators, often considered to subsidize terrestrial food webs. However, larval aquatic insects themselves consume both aquatic primary producers and allochthonous terrestrial detritus, suggesting that adults could provide aquatic subsidy and/or recycled terrestrial energy to terrestrial consumers. Understanding the source of carbon (aquatic vs. terrestrial) driving aquatic insect emergence is important for predicting magnitude of emergence and effects on recipient food web dynamics; yet direct experimental tests of factors determining source are lacking. Here, we use Culex mosquitoes in experimental pools as an exemplar to test how variation in general factors common to aquatic systems (terrestrial plant inputs and light) may alter the source and amount of energy exported to terrestrial ecosystems in adult aquatic insects that rely on terrestrial resources as larvae. We found strong sequential effects of terrestrial plant inputs and light on aquatic insect oviposition, diet, and emergence of Culex mosquitoes. Ovipositing mosquitoes laid ~3 times more egg masses in high terrestrial input pools under low light conditions. This behavior increased adult emergence from pools under low light conditions; however, high input pools (which had the highest mosquito densities) showed low emergence rates due to density-dependent mortality. Mosquito diets consisted mainly of terrestrial resources (~70–90 %). As a result, the amount of aquatic carbon exported from pools by mosquitoes during the experiment was ~18 times higher from low versus high light pools, while exports of terrestrial carbon peaked from pools receiving intermediate levels of inputs (3–6 times higher) and low light (~6 times higher). Our results suggest that understanding the interplay among terrestrial plant inputs, light availability and biotic responses of aquatic insects may be key in predicting source and magnitude of emergence, and thus the strength and effects of aquatic–terrestrial linkages in freshwater systems.     

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.     

Effect of habitat complexity on the predation of Buenoa fuscipennis (Heteroptera: Notonectidae) on mosquito immature stages and alternative prey

Notonectids are well‐known predators in aquatic habitats, where mosquito larvae, chironomids, and cladocerans constitute their main diet. Our purpose was to assess the effect of structural complexity on the predatory ability of Buenoa fuscipennis, a common predator in aquatic habitats of Buenos Aires city (Argentina). Buenoa fuscipennis showed type 2 functional responses in both the presence and absence of prey refuge and no differences in attack rate or handling time between refuge treatments. Regarding mosquito size classes, B. fuscipennis exhibited a significantly higher preference for 2^nd instar larvae and no predation on pupae. In the presence of mosquito larvae and alternative prey, B. fuscipennis preferred mosquitoes over chironomid larvae and adult cladocerans over mosquito larvae. No switching behavior was detected in our experiments. Habitat structure only slightly affected the predator´s consumption rates on mosquito larvae. Overall, preference for prey did not vary with the presence of refuge, except for the preference for mosquitoes over chironomid larvae, which was significantly decreased in the presence of refuge as a consequence of reduced predation on mosquito larvae. The results suggest that B. fuscipennis could efficiently control mosquitoes in structurally simple habitats where chironomids are the most abundant alternative prey but not in temporary pools where cladocerans are abundant.     

Nestedness patterns of container-dwelling mosquitoes: effects of larval habitat within variable terrestrial matrices

Distributions of mosquito larvae likely are a consequence of multiple factors, although two commonly studied factors (quality of the larval environment and the terrestrial matrix in which these habitats reside) have rarely and simultaneously been varied in the field to understand distributions of larvae. We monitored aquatic containers of two leaf detritus levels within a forest, prairie, and industrial habitat across five months to understand the temporal and spatial colonization of aquatic invertebrates in Northcentral Illinois, USA. Data were collected monthly on mosquito populations and the composition of other invertebrates colonizing containers. Overall, six species of mosquitoes colonized containers, with Culex restuans and Aedes triseriatus having the highest relative abundances. There were strong seasonal abundance patterns for these two mosquito species, with the dominant species changing over time in the forest habitat. The responses of other mosquito taxa were more variable, with abundances reflective of either the terrestrial matrix or larval habitat quality. High detritus containers supported the highest abundances of most species encountered, regardless of habitat. Non-mosquito taxa were less common numerically, but analyses suggested that some taxa, such as syrphid larvae, often co-occurred with mosquitoes. Nested subset analysis indicated communities were strongly nested, and that both habitat type and detritus level were important in explaining nested patterns of aquatic invertebrates. Our data show that both the larval habitat and the surrounding terrestrial matrix shape patterns of container mosquitoes, and that other container invertebrates vary in similar ways as mosquitoes. Handling editor: K. Martens     

Wetland isolation facilitates larval mosquito density through the reduction of predators

• 1 Wetlands harbour high biodiversity and offer important ecosystem services, but they are also a habitat for mosquito larvae (Diptera: Culicidae), which are important disease vectors.
• 2 Isolation among remnant, or newly created wetlands and ponds, and their consequent density in the landscape, is a key factor that can influence a variety of food web processes, including effects on mosquitoes which are important prey to many predators.
• 3 We assess the impact of habitat isolation on the density of pond‐breeding mosquitoes (several Anopheles and Culex species) both directly and indirectly through the food web.
• 4 Results from structural equation modelling of survey data shows that larval mosquitoes are denser in ponds that are more isolated from one another, and that this result was primarily driven indirectly by a reduction of larval mosquito predators (e.g. predaceous insects and amphibians). Furthermore, results from a long‐term mesocosm experiment factorially manipulating isolation and predator reduction show that the effect of isolation on mosquito density was eliminated when predators were experimentally reduced.
• 5 It is concluded that metacommunity processes, both directly and indirectly mediated through predators, can play an important role in the local abundance of wetland breeding mosquitoes and possibly the diseases they spread.

     

Impact of field‐realistic doses of glyphosate and nutritional stress on mosquito life history traits and susceptibility to malaria parasite infection

Glyphosate is the world's most widely used herbicide. The commercial success of this molecule is due to its nonselectivity and its action, which would supposedly target specific biosynthetic pathways found mainly in plants. Multiple studies have however provided evidence for high sensitivity of many nontarget species to glyphosate and/or to formulations (glyphosate mixed with surfactants). This herbicide, found at significant levels in aquatic systems through surface runoffs, impacts life history traits and immune parameters of several aquatic invertebrates' species, including disease‐vector mosquitoes. Mosquitoes, from hatching to emergence, are exposed to aquatic chemical contaminants. In this study, we first compared the toxicity of pure glyphosate to the toxicity of glyphosate‐based formulations for the main vector of avian malaria in Europe, Culex pipiens mosquito. Then we evaluated, for the first time, how field‐realistic dose of glyphosate interacts with larval nutritional stress to alter mosquito life history traits and susceptibility to avian malaria parasite infection. Our results show that exposure of larvae to field‐realistic doses of glyphosate, pure or in formulation, did not affect larval survival rate, adult size, and female fecundity. One of our two experimental blocks showed, however, that exposure to glyphosate decreased development time and reduced mosquito infection probability by malaria parasite. Interestingly, the effect on malaria infection was lost when the larvae were also subjected to a nutritional stress, probably due to a lower ingestion of glyphosate.     

Mosquito fauna inhabiting water bodies in the urban environment of Córdoba city,Argentina, following a St. Louis encephalitis outbreak

An understanding of urban aquatic environments as mosquito larval habitats is necessary to prioritize sites for surveillance and control of arbovirus vectors in urban areas. Natural and artificial water bodies at ground level that may be larval mosquito habitats in Córdoba city, Argentina were surveyed. Data on the characteristics of aquatic sites and the presence and abundance of mosquito larvae and pupae were collected in the summer of 2006, coinciding with the first report of human WNV and following an outbreak of St. Louis encephalitis in 2005. Eight species in the genera Aedes, Culex, and Mansonia were identified. At 64.2% (34 of 53) of the sites, only one species was collected, while 3.8% (2 of 53) had three associated species, the highest richness found per site. Culex quinquefasciatus represented over 99% (out of 32,729) of the specimens. It was also the most widely distributed and detected under diverse habitat conditions. Although puddles and semi‐permanent pools harbored a greater number of species, drainages and channels may be more relevant as risk factors from an epidemiological point of view because they showed the highest larval densities, mainly of Cx. quinquefasciatus (vector of SLE and WNV). Also, higher densities of this species were associated with stormwater runoff and sewage water, thus water management systems should be targeted and closely monitored for mosquito control purposes.     

Noncrop flowering plants restore top‐down herbivore control in agricultural fields

Herbivore populations are regulated by bottom‐up control through food availability and quality and by top‐down control through natural enemies. Intensive agricultural monocultures provide abundant food to specialized herbivores and at the same time negatively impact natural enemies because monocultures are depauperate in carbohydrate food sources required by many natural enemies. As a consequence, herbivores are released from both types of control. Diversifying intensive cropping systems with flowering plants that provide nutritional resources to natural enemies may enhance top‐down control and contribute to natural herbivore regulation. We analyzed how noncrop flowering plants planted as “companion plants” inside cabbage (Brassica oleracea) fields and as margins along the fields affect the plant–herbivore–parasitoid–predator food web. We combined molecular analyses quantifying parasitism of herbivore eggs and larvae with molecular predator gut content analysis and a comprehensive predator community assessment. Planting cornflowers (Centaurea cynanus), which have been shown to attract and selectively benefit Microplitis mediator, a larval parasitoid of the cabbage moth Mamestra brassicae, between the cabbage heads shifted the balance between trophic levels. Companion plants significantly increased parasitism of herbivores by larval parasitoids and predation on herbivore eggs. They furthermore significantly affected predator species richness. These effects were present despite the different treatments being close relative to the parasitoids’ mobility. These findings demonstrate that habitat manipulation can restore top‐down herbivore control in intensive crops if the right resources are added. This is important because increased natural control reduces the need for pesticide input in intensive agricultural settings, with cascading positive effects on general biodiversity and the environment. Companion plants thus increase biodiversity both directly, by introducing new habitats and resources for other species, and indirectly by reducing mortality of nontarget species due to pesticides.     

Stable isotope analysis of larval mosquito diets in agricultural wetlands in the coastal plain of Georgia,U.S.A.

Previous studies have used C and N isotope ratios to investigate the use of different food resources such as plant and animal detritus by container‐breeding mosquitoes. This study is the first to report on the potential food resources assimilated by larval mosquitoes in agricultural and reference wetlands. Larval mosquitoes (Diptera: Culcidae) were sampled, along with their potential food resources, from agricultural and reference wetland habitats throughout a seasonal hydroperiod. IsoSource mixing model results indicated that food resources had greater δ¹⁵N isotope values in agricultural wetlands compared with cypress‐gum swamps. In February, Aedes vexans (Meigen) and Culex territans Walker larvae fed primarily on lower quality food resources (coarse particulate organic matter and sediment) based on C:N. In contrast, higher quality food resources (fine particulate organic matter) were utilized by Anopheles spp. throughout the study and by Psorophora columbiae (Dyer and Knab) in May. This research contributes to a more comprehensive understanding of the food resources available and assimilated by larval mosquitoes in agricultural wetlands.     

Pond attributes influence competitive interactions between tadpoles and mosquito larvae

Abstract Tadpoles and mosquito larvae often coexist in natural freshwater bodies. We studied competitive interactions between: (i) tadpoles of the striped marsh frog (Limnodynastes peronii) and larvae of the mosquito Culex quinquefasciatus; and (ii) tadpoles of the common eastern froglet (Crinia signifera) and larvae of the mosquito Aedes australis. These two sets of taxa occur in natural water bodies in the Sydney region. Laboratory trials revealed competition between mosquito larvae and tadpoles in both systems. For example, mosquitoes displayed reduced rates of survival, growth and development, and smaller size at metamorphosis, when they were raised with tadpoles. The intensity of competitive suppression was influenced by attributes such as pond size (and hence, larval density), the location of food (on the water surface vs the substrate), and the extent of opportunities for direct physical interactions between the two competing organisms. These effects differed between the two study systems, suggesting that the mechanisms of suppression also differed. Limnodynastes peronii tadpoles suppressed C. quinquefasciatus even when the two types of organisms were separated by a physical partition, suggesting that chemical or microbiological cues may be responsible. Pond attributes also affected the impact of C. signifera tadpoles on Aedes larvae, but (unlike the Limnodynastes–Culex system) these effects disappeared when densities were lowered or when the tadpoles and mosquito larvae were physically separated. Thus, direct physical interactions may suppress mosquitoes in the Crinia–Aedes system. Our results suggest that tadpoles suppress the viability of larval mosquitoes by multiple pathways.