Attracted to the enemy: Aedes aegypti prefers oviposition sites with predator-killed conspecifics

Oviposition habitat choices of species with aquatic larvae are expected to be influenced by both offspring risk of mortality due to predation, and offspring growth potential. Aquatic predators may indirectly influence growth potential for prey by reducing prey density and, for filter-feeding prey, by increasing bacterial food for prey via added organic matter (feces, partially eaten victims), creating the potential for interactive effects on oviposition choices. We tested the hypothesis that the mosquito Aedes aegypti preferentially oviposits in habitats with predatory Toxorhynchites larvae because of indirect effects of predation on chemical cues indicating bacterial abundance. We predicted that A. aegypti would avoid oviposition in sites with Toxorhynchites, but prefer to oviposit where bacterial food for larvae is abundant, and that predation by Toxorhynchites would increase bacterial abundances. Gravid A. aegypti were offered paired oviposition sites representing choices among: predator presence; the act of predation; conspecific density; dead conspecific larvae; and bacterial activity. A. aegypti preferentially oviposited in sites with Toxorhynchites theobaldi predation, and with killed conspecific larvae, but failed to detect preferences for other treatments. The antibiotic tetracycline eliminated the strongest oviposition preference. Both predation by Toxorhynchites and killed larvae increased bacterial abundances, suggesting that oviposition attraction is cued by bacteria. Our results show the potential for indirect effects, like trophic cascades, to influence oviposition choices and community composition in aquatic systems. Our results suggest that predators like Toxorhynchites may be doubly beneficial as biocontrol agents because of the attraction of ovipositing mosquitoes to bacterial by-products of Toxorhynchites feeding.

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title: Modelling evolutionarily stable strategies in oviposition site selection, with varying risks of predation and intraspecific competition
abstract: Many ovipositing mosquitoes, as well as other species, can detect biotic factors that affect fitness. However, a female mosquito seeking a high quality oviposition site (e.g. one with low risk of predation and competition to her progeny) must often balance the competing risk of increasing probability of mortality to herself while she continues to search, against increased probability of finding a high quality site. Such oviposition site selection may affect adult population size. We examined a female mosquito’s expected strategy of oviposition site selection under conditions of varying predator prevalence and adult mortality risk, by combining a detailed structured population model with a Markov chain implementation of the adult behavioural process. We used parameter values from the specific mosquito-predator system, Culiseta longiareolata-Notonecta maculata, although the overall results can be generalised to many mosquito species. Our model finds the evolutionarily stable strategy of oviposition site selection for different parameter combinations. Our model predicts that oviposition strategy does not vary smoothly with varying environmental risk of adult mortality, but that certain oviposition strategies become unstable at some parameter values. Mosquitoes will distribute their reproductive effort between breeding sites of varying predation risk only when adult mortality is low or larval competition high. Our model predicts that females will continue searching for predator-free pools, rather than oviposit in the first site encountered, regardless of the risk of mortality to the adult. The ecological basis for a reproductive strategy with alternative behaviours is important for understanding the effect of biotic factors on the population dynamics of mosquitoes, and for the development of biological control strategies, such as the dissemination of predator-cue chemicals.

title: Oviposition Site Choice and Life History Evolution
abstract: SYNOPSIS. Studies of life history evolution, as well as much of life history theory, have typically focused on "hard" components of life histories; phenotypic characteristics that can be readily observed, quantified, and ultimately, connected rather directly to fitness. Typical of these are propagule size, propagule number, and age and size at maturity. What is largely missing from the study of life history evolution is consideration of the role of behavior, principally female oviposition site choice, in the evolution of life histories. For oviparous organisms, natural selection cannot produce locally optimized "hard" components of life history phenotypes without a consistent environmental context (whether invariant or variable); in a variable environment, that consistent environmental context can be most effectively provided by interactive oviposition site choice. I present a model of selection on oviposition site choice in the context of the evolution of "hard" components of life history phenotypes, along with some experimental data illustrating oviposition site choice in response to predators. The model and data are then related to the overall question of the role of oviposition site choice in life history evolution. The conclusion is that oviposition site choice must be under equally strong selection with egg size, egg number and the other hard components of life histories in order to generate and optimize locally adapted or ecologically specialized life history phenotypes, and must therefore, play a significant role in the evolution of life histories.

title: THE ONTOGENETIC NICHE AND SPECIES INTERACTIONS IN SIZE-STRUCTURED POPULATIONS
abstract: Body size is manifestly one of the most important attributes of an organism from an ecological and evolutionary point of view. Size has a predominant influence on an animal's energetic requirements, its potential for resource exploitation, and its susceptibility to natural enemies. A large literature now exists on how physiological, life history, and population parameters scale with body dimensions (24, 131). The ecological literature on species interactions and the structure of animal communities also stresses the importance of body size. Differences in body size are a major means by which species avoid direct overlap in resource use (153), and size-selective predation can be a primary organizing force in some communities (20, 70). Size thus imposes important constraints on the manner in which an organism interacts with its environment and influences the strength, type, and symmetry of interactions with other species (152, 207). Paradoxically, ecologists have virtually ignored the implications of these observations for interactions among species that exhibit size-distributed populations. For instance, it has been often suggested that competing species

title: Colonization under threat of predation: avoidance of fish by an aquatic beetle, Tropisternus lateralis (Coleoptera: Hydrophilidae)
abstract: Documenting the role of past interactions in the assembly of present communities has proven problematic. Colonization is a key process in community assembly that is both potentially driven by past interactions and amenable to experimental approaches. Colonization and oviposition by an aquatic beetle (Tropisternus lateralis) was assayed in the presence and absence of both 'harmless' and tactilely/visually isolated predatory fish (Lepomis gibbosus and L. macrochirus). Beetles avoided each treatment with fish when compared to fish-free experimental pools. Activity levels after colonization also differed significantly between adults in fish and fish-free tanks. Predator effects on species composition are typically ascribed to contemporary predation events; the presence of a strong avoidance response demonstrates that past species interactions affect present distributions and may play an important role in the ongoing assembly of contemporary communities. Documentation of such avoidance behavior in a growing number of species fundamentally alters our view of the processes affecting species distributions and the process of community assembly.

title: Chemical detection of the predator Notonecta irrorata by ovipositing Culex mosquitoes.
abstract: We tested the oviposition response of Culex mosquitoes to the predator Notonecta irrorata in an outdoor artificial pool experiment employing equal numbers of control and predator pools. There was a strong oviposition avoidance by Culex of Notonecta pools; 83% of egg rafts were found in control pools during the period in which Notonecta were present. After removing Notonecta, mosquitoes continued to avoid ovipositing in the former Notonecta pools for two additional days suggesting a predator-released kairomone as the cue used by the mosquitoes to detect the presence of this predator.

title: Predator effects on aquatic community assembly: disentangling the roles of habitat selection and post-colonization processes
abstract: Top predators are known to play an important role in the assembly of communities via two mechanisms: (1) by altering the colonization (or emigration) patterns of prey through behavioral habitat selection, and (2) by altering vital rates (e.g. mortality, birth) of prey after colonization. While both these mechanisms act to determine assembly, research has focused on either their combined overall effects (confounding them), or examined them singly. As a result, it remains unclear how these mechanisms act to sequentially shape community structure. In this study, we experimentally disentangle habitat selection and post-colonization effects of predaceous fish to test their independent and combined influence on the assembly of insect and larval amphibian communities in experimental freshwater habitats. Specifically, we ask, ‘do the behavioral choices of colonists continue to structure aquatic communities even after post-colonization processes have occurred?’ Like previous studies, we found that colonization was strongly reduced by the presence of fish cues. More importantly, these effects of fish on prey colonization behavior combined independently with post-colonization processes to determine the overall effect of predators on community assembly. Although habitat selection and predation both reduced abundance and biomass of most taxa in the post-colonization communities, these factors had qualitatively different effects on aspects of trophic structure. Habitat selection altered the ratio of secondary to primary consumer abundance and biomass, while post-colonization predation drove strong trophic cascades not observed in response to habitat selection. Our results suggest that behavioral choices regarding habitat selection can have lasting and unique effects on the structure of aquatic communities.

title: PREDATOR-INDUCED SHIFTS IN MOSQUITO OVIPOSITION SITE SELECTION: A META-ANALYSIS AND IMPLICATIONS FOR VECTOR CONTROL
abstract: The global resurgence and emergence of new mosquito-borne diseases and increasing resistance of mosquitoes to chemical pesticides have prompted renewed interest in biocontrol methods that use aquatic predators of mosquito larvae. For disease vectors with complex life cycles, like mosquitoes, in which adults are terrestrial and choose aquatic habitats in which to deposit their offspring, shifts in oviposition site selection may have important consequences for vector population dynamics and epidemiology. While there have been numerous studies of mosquito oviposition site selection, methodology and results vary, making it difficult to evaluate the general importance of predator-induced shifts in oviposition site selection for biocontrol scenarios. Here we use meta-analysis to provide a quantitative framework for examining variation in mosquito oviposition responses to predators. Overall, we find a broad pattern of predator avoidance among mosquito and predator taxa. The primary factor explaining variation in...

title: Choice of Oviposition Site by Hyla Chrysoscelis: Role of Predators and Competitors
abstract: The role of predators and competitors in the choice of oviposition site by the treefrog Hyla chrysoscelis was examined in a randomized complete block experiment using 90 replicated experimental ponds. Control ponds containing neither predators nor competitors were contrasted with treatment ponds into which one of four species of predators (Ambystoma maculatum larvae, Enneacanthus chaetodon adults, Notophthalmus viridescens adults, Tramea carolina larvae) or one of two species of competitors (Rana catesbeiana, Hyla chrysoscelis) was added. Treatments had significant effects on the mean number of eggs deposited in ponds. Fewer eggs were laid in ponds with Ambystoma, Enneacanthus, or Hyla, as a result of fewer females laying eggs and fewer eggs laid per visit, compared with control ponds. Notophthalmus, Rana, and Tramea had no effect on the number of eggs laid. Ovipositing Hyla discriminated among potential oviposition sites based on the species present. Choice of oviposition site can determine the success of a female's reproductive investment, and it can be a mechanism affecting the structure of ecological communities as well. Our results emphasize the importance of oviposition site choice in the evolution of reproductive patterns and implicate species avoidance by ovipositing females as a mechanism important in generating variability in ecological communities.

title: LARVAL PERFORMANCE AND OVIPOSITION SITE PREFERENCE ALONG A PREDATION GRADIENT
abstract: The ability of females to assess habitat quality for offspring can strongly influence individual reproductive success as well as population dynamics and community assembly. However, the specific relationship between oviposition site selection and larval performance is often unclear. Ovipositing females of several species of treefrogs (Hyla) avoid predatory fish. The fish density required to elicit such avoidance and its relationship to larval performance are central to our understanding of how behavior can drive population dynamics and community assembly in complex landscapes. We conducted experiments investigating both oviposition preference and larval performance in pinewoods treefrogs (Hyla femoralis) along a density gradient of predatory fish (0-6 Umbra pygmaea). Female H. femoralis detected and strongly avoided the nonlethal presence of even a single 2-g fish, ovipositing almost exclusively in predator-free controls. In a separate experiment, larval performance largely matched adult preferences; larvae were totally eliminated in all but the lowest fish density. Given a landscape of breeding sites of varying risks, ovipositing H. femoralis behaviorally partition available habitats into those with and without fish, largely matching the associated fitness consequences.

title: Reproductive decisions under threat of predation: squirrel treefrog (Hyla squirella) responses to banded sunfish (Enneacanthus obesus)
abstract: We tested whether the presence of a predator (non-lethal effect) could produce patterns of prey distribution and abundance attributed historically to direct mortality. Sixteen experimental ponds (1,000 l cattle watering tanks) were established; eight containing seven enclosed banded sunfish, Enneacanthus obesus, and eight predator-free controls. Ponds were colonized by ovipositing squirrel treefrogs, Hyla squirella, and a total of 33,128 eggs and tadpoles were recovered from the experimental ponds. Significantly more eggs and tadpoles (94.8%) were recorded from the predator-free treatments. These data support an alternative mechanism, based primarily on maternal behavior, explaining classic patterns of anuran species composition across a landscape of breeding sites.

title: DO PREDATOR CHEMICAL CUES AFFECT OVIPOSITION SITE SELECTION IN NEWTS
abstract: Predation on larval stages has been reported to play an important role in structuring amphibian communities, and for this reason the choice of suitable oviposition places is likely to influence newt fitness. In this study, we assessed whether females of four newt species - marbled newt (Triturus marmoratus), alpine newt (T. alpestris), palmate newt (T. helveticus) and Boscas newt (T. boscai) - avoid chemical cues of predatory brown trout ( Salmo trutta) in selecting their oviposition site. In laboratory tests, individual females were allowed to choose their oviposition site between places with water conditioned by fish chemicals and others with unconditioned water. T. marmoratus females selected preferentially tubs without predator cues as oviposition sites, whereas the other three species did not show significant preference under these conditions. Absence of chemical recognition capabilities, strong philopatry towards oviposition site or predator avoidance based in habitat characteristics are suggested as possible causes of the lack of chemical predator avoidance detected in this experiment.

title: Incorporating density dependence into the oviposition preference-offspring performance hypothesis.
abstract: 1. Although theory predicts a positive relationship between oviposition preferences and the developmental performance of offspring, the strength of this relationship may depend not only on breeding site quality, but also on the complex interactions between environmental heterogeneity and density-dependent processes. Environmental heterogeneity may not only alter the strength of density dependence, but may also fundamentally alter density-dependent relationships and the preference-performance relationship. 2. Here I present results from a series of field experiments testing the effects of environmental heterogeneity and density-dependent feedback on offspring performance in tree-hole mosquitoes. Specifically, I asked: (i) how do oviposition activity, patterns of colonization and larval density differ among habitats and among oviposition sites with different resources; and (ii) how is performance influenced by the density of conspecifics, the type of resource in the oviposition site, and the type of habitat in which the oviposition site is located? 3. Performance did not differ among habitats at low offspring densities, but was higher in deciduous forest habitats than in evergreen forest habitats at high densities. Oviposition activity and larval densities were also higher in deciduous forests, suggesting a weak preference for these habitats. 4. The observed divergence of fitness among habitats with increasing density may select for consistent but weak preferences for deciduous habitats if regional abundances vary temporally. This would generate a negative preference-performance relationship when population densities are low, but a positive relationship when population densities are high. 5. This study demonstrates that failure to recognize that fitness differences among habitats may themselves be density-dependent may bias our assumptions about the ecological and evolutionary processes determining oviposition preferences in natural systems.

title: Predation‐dependent oviposition habitat selection by the mosquito Culiseta longiareolata: a test of competing hypotheses
abstract: We investigated the mechanism underlying oviposition habitat selection (OHS) in the mosquito Culiseta longiareolata. The putative outcome of a trade-off between the risk of predation and detrimental density dependence, OHS in this species presents an opportunity to test two competing alternatives: (1) a polymorphic scenario, in which a fixed proportion of females constantly avoid ‘predator pools’, while the remainder oviposits at random; and (2) a monomorphic scenario, in which all females oviposit in predator pools with a certain probability. We present a conceptual framework that demonstrates how a simple experimental design – whereby predator incidence in artificial pools is alternated between 0.25 and 0.75 – can distinguish between, or refute, the two scenarios. Given the proportional use, by ovipositing females, of predator-free pools observed under each treatment, and a bootstrap estimate of the ratio of daily oviposition rates, we find the monomorphic scenario twice as likely as the polymorphic.

title: Amazon poison frogs (Ranitomeya amazonica) use different phytotelm characteristics to determine their suitability for egg and tadpole deposition
abstract: Parents have to assess the multivariate characteristics of their reproductive sites to maximize their reproductive success through offspring performance. In addition, they may provide care to ensure optimal performance of their offspring. In poison frogs it has been identified that ecological characteristics of reproductive sites may underlie transitions in the involvement of parental sexes in care for offspring. To elucidate the ecological factors that may drive these transitions, it is important to understand which characteristics poison frogs use to assess the quality of their reproductive site. We studied the use of small water bodies in leaf axils of bromeliads, phytotelmata, for egg and tadpole deposition by Amazon poison frogs (Ranitomeya amazonica). We compared phytotelm quality characteristics for preferred egg and tadpole deposition sites and used two choice tests with plastic cups to study the causal relationship with tadpole deposition for the identified characteristics. The differences among quality characteristics of deposition sites were largest among bromeliad species, and for egg or tadpole deposition different bromeliad species were preferred. However, males were also selective in the leaf axils within a bromeliad species that they used for egg or tadpole deposition. Eggs were deposited in small, resource limited water bodies that were close to the forest floor. Tadpoles were deposited in leaf axils holding resource-rich phytotelmata with larger water volumes. Preference of detritus containing water over clear water in choice tests confirmed that Amazon poison frogs assess quality of their tadpole deposition sites on food availability. We conclude that preference for large water volume and resource rich phytotelmata plays an important role in determining male involvement in parental care and speculate that distribution of preferred resources may bring about selection on female involvement in parental care.

title: Oviposition habitat selection by container‐dwelling mosquitoes: responses to cues of larval and detritus abundances in the field
abstract: Insects' oviposition responses to resource and larval densities can be important factors determining distributions and competitive interactions of larvae. Aedes albopictus (Skuse) and Aedes aegypti (L.) (Diptera: Culicidae) show aggregated distributions of larvae in the field, larval interactions that are affected by detritus resources, and oviposition responses to resource and density cues in the laboratory. In this study, field experiments were conducted to test whether these species choose oviposition sites in response to chemical cues indicating detritus resource quantity and quality or larval abundances. In Experiment 1, both species showed interactive responses to water conditioned with high or low quantities of senescent live oak leaves and density combinations of A. albopictus and A. aegypti larvae. Aedes aegypti preferred high‐detritus containers when conspecifics were absent. Aedes albopictus tended to prefer high‐detritus containers when larval density was low. We found no evidence of interspecific differences in oviposition preferences. In Experiment 2, A. albopictus preferred high detritus to low or no detritus, and rapidly decaying, high‐quality detritus to low‐quality detritus. Oviposition choices by these Aedes are mainly determined by resource quantity and quality, with larval densities having minor, variable effects. Oviposition responses of these species are unlikely to lead to resource partitioning. Aggregated distributions of these species in the field are unlikely to be products of oviposition choices based on larval densities.

title: Laboratory studies on oviposition behaviour of Culex quinquefasciatus Say (Diptera: Culicidae): choice of oviposition medium and oviposition cycle.
abstract: The preference of Culex quinquefasciatus Say for oviposition in rearing water (in which larvae and pupae of the same species had been reared), pond water, tap water (from a well) deionised water and food water (in which larval food was mixed) was tested in a 5 × 5 Latin square. Most oviposition occurred in rearing water, followed in decreasing order by pond water, tap water, deionised water and food water, the differences being significant except between pond water and tap water. Diel oviposition activity of females from wild-caught pupae was studied under tropical normal (light-day) photoperiod (LD 12:12), reversed (dark-day) photoperiod (DL 12:12) and continuous light (LL) for at least three consecutive days at average conditions of 29·3°C and 91% RH. Under conditions of alternate light and dark periods (normal as well as reversed), there was a circadian rhythm, which was unimodal, confined to the scotophase and concentrated in the first half of the scotophase. Under continuous light, activity was greatly depressed, with disturbances both in circadian rhythm and unimodality. It is concluded that the circadian rhythm of oviposition activity of C. quinquefasciatus is predominantly exogenous in nature and regulated mainly by photoperiod, activity being stimulated by darkness and inhibited by light.

title: Oviposition by African malaria vector mosquitoes. II. Effects of site tone, water type and conspecific immatures on target selection by freshwater Anopheles gambiae Giles, sensu lato.
abstract: Females of Anopheles gambiae s. lat., most of which would have been A. gambiae s. str., were collected from houses in coastal Kenya and tested for their oviposition preferences using Petri dishes in large laboratory cages with lighting equivalent to weak moonlight. Significantly more eggs were laid overnight in water over black than over paler tones, and this difference increased as contrast with the surrounding floor was increased. Direct observation revealed that over white targets, females oviposited from a settled posture, whereas over black targets they did so from flight. The influence on this behaviour of target darkness (tone) overrode that of cage size or target size. In tests which yielded markedly fewer eggs in sea water than in tap water, no significant difference was detected when cage floors were either black or white, although a black floor might have resulted in significantly greater discrimination against sea water had more tests been conducted. All further testing was done over black cage floors. Turbid water from a natural development site received more eggs than distilled, tap or swamp water, even though the turbid water appeared paler than the others. The females did not discriminate between rearing water and tap water, or tap water with and without pupae, but the presence of larvae was repellent. Turbid water from a development site thus seemed to possess an arrestant property which overrode selection favouring darker targets, and which was not derived from prior presence of conspecific immatures. It is suggested that for A. gambiae, oviposition from a settled posture is a response to sub-optimal stimuli, possibly indicating conditions under which oviposition would not occur in nature, and hence why cage experiments using white targets have in the past yielded confusing results.

title: An oviposition attractant pheromone in culex-quinquefasciatus say (diptera, culicidae)
abstract: Gravid females of Culex quinquefasciatus Say from a laboratory strain originating in Nigeria orientated to a source of the main volatile pheromone component, erythro -6-acetoxy-5-hexadecanolide, isolated from the apical droplets of the egg rafts. Significantly more egg rafts were laid around polystyrene discs treated with the synthetic compound than around untreated discs, and modification of the chemical structure destroyed its biological activity. The response was found at a dose of 0·02μg of the synthetic compound, which is equivalent to one-sixteenth of the total acetoxyhexadecanolide found in an egg raft, and above. Although the apical droplets were contaminated by bacteria, these did not contribute to the production of the acetoxyhexadecanolide, which was present in the eggs before they were laid. It is concluded that the pheromone is released slowly from the apical droplets into the air above the water surface, attracting other gravid females to oviposit around previously laid egg rafts, and there is evidence of attraction over a distance of 5·5 cm.

title: A seasonal shift in egg-laying behaviour in response to cues of future competition in a treehole mosquito
abstract: We tested a set of hypotheses to predict egg-laying behaviour in Aedes tr.isevintus in the field in Massachusetts. These hypotheses reflect three main themes: females avoid competitive or predatory threats to their larvae; feinales judge larvae or eggs as cues to future perinaileilce or productivity within a treehole; and females are either opportunistic ovipositors, or hedge their bets by scattering their eggs in multiple habitats. We predicted that ~nosquitoes might vary in their response depeilding on whether their offspring will hatch immediately or enter diapause and hatch the next year. 2. We stocked artificial treeholes with larvae at four densities ranging froin 0 to 90 larvae per habitat for four trials in 1992 and eight trials in 1994. In 1992, we added predatory Anopheles barbevi larvae to half the replicates of each density level. 111 1994, we tested for an interactio~l between egg and larval density by stocking additional traps with eggs in batches of 0, 20 and 200, and larvae in densities as in the previous trials. 3. The population revealed a significant interaction between time of year and larval density. More eggs accumulated in traps stocked with fewer larvae (0 or 15) early in the season, but fenlales showed a slight positive response to higher densities (45 or 90) later on, after their offspring were all likely to enter diapause. These results suggest that potential ambiguities of larval cues, with indications of habitat permanence as well as adversity of future competition, are resolved by females. Fenlales did not respoild differentially to the predatory Anopheles barberi larvae. 4. The estimated batch size obtained in oviposition traps did not differ from the fecundity of field-caught fe~nales allowed to oviposit under confinenlent in laboratory vials, suggesting that bet-hedging by scattering of eggs anlong multiple habitats did not occur. 5. An unexpected result, a positive response to higher egg densities, is discussed in light of studies on other insects. This result conflicts with our predictions based 011 fe~nales choosing less competitive environn~ents for their larvae and also co~lflicts with previously published accounts of avoidance of eggs in this species. Preference for habitats with conspecific eggs inight be explained if eggs reflect habitat stability or if larvae gain an advantage fro~n being in an aggregation. Neither hypothesis is resolved by the present study.  Aedes, competitioi~, density-dependent, habitat selection, oviposition

title: NUTRIENT DYNAMICS, BACTERIAL POPULATIONS, AND MOSQUITO PRODUCTIVITY IN TREE HOLE ECOSYSTEMS AND MICROCOSMS'
abstract: Water-filled treeholes provide an experimental setting for examining pro- cesses within an ecosystem, and influences of external factors on those processes. Using a limnological, experimental approach involving both natural tree holes and laboratory mi- crocosms of the tree hole ecosystem, we identified and studied interacting, biotic processes, including dynamics of bacterial populations and variation in concentration of inorganic nutrients in tree hole water, and density-dependent competition for food among larvae of the mosquito Aedes triseriatus. We characterized the influence of external factors (inputs of leaf detritus and stemflow) on those processes. Analyses of water samples over time showed that tree hole water was rich and dynamic in nutrients (nitrite, nitrate, ammonium, phosphate, and sulfate); ammonium was the dominant form ofinorganic nitrogen. Variation in nutrient concentrations in microcosms depended upon exogenous inputs (leaf detritus and stemflow water), dilution of nutrients by stemflow, nutrient cycling processes (nitri- fication, denitrification, and sulfate reduction), and ammonium excretion by mosquito larvae. The densities of bacteria in tree hole water, obtained using direct counts of DAPI- fluorochrome stained samples and epifluorescence microscopy, ranged from 2.0 x 106 to 6.0 x 107 cells/mL, and in microcosms from 4.6 x 105 to 2.6 x 108 cells/mL. Experi- mentation involving microcosms revealed that bacterial abundance was reduced by mos- quito feeding and stemflow flushing. Further experiments showed that stemflow flushing increased mosquito productivity from microcosms several-fold and released mosquitoes from density-dependent competition. This effect was likely related to nutrient input and the simultaneous removal of toxic metabolites owing to inputs of stemflow water. We conclude that disturbance by a physical factor, stemflow, has a major influence on the interactions of nutrient dynamics, bacterial populations, and mosquito productivity in temperate tree-hole ecosystems.

title: Evaluation of organic infusions and synthetic compounds mediating oviposition inAedes albopictus andAedes aegypti (Diptera: Culicidae)
abstract: Oviposition responses of gravidAedes albopictus andAe. aegypti were evaluated to natural organic infusions (hay infusion, larval rearing water, and field-collected larval water) as well as compounds isolated from hay infusion (3-methylindole, 4-methylphenol, 4-ethylphenol, indole, and phenol) known to elicit oviposition inCulex mosquitoes. In laboratory bioassays, significant oviposition responses were obtained fromAe. albopictus, but not fromAe. aegypti, to dilutions of hay infusion and field water. Oviposition responses of both species were moderate to the synthetic compounds tested in the laboratory (0.01–100 µg/liter). Only 3-methylindole (0.1 µg/liter) and 4-ethylphenol (1.0 µg/liter) elicited significantly more oviposition byAe. albopictus than did well water. Of the synthetic compounds tested withAe. aegypti, only phenol (1.0 µg/liter) and 4-ethylphenol (0.1 µg/liter) elicited significantly more oviposition than did well water. Significant repellency or oviposition deterrence for both species occurred in response to at least one high concentration of most of the compounds tested. In field cage evaluations, oviposition responses byAe. albopictus were strongest to larval water and field water, moderate to hay infusion and 3-methylindole (100 µg/liter), and low to well water. A mixture of five synthetic compounds mimicking hay infusion was no more effective than 3-methylindole alone. ForAe. aegypti, oviposition responses were greatest to larval water and least to 3-methylindole. In an olfactometer, gravid females of both species oriented more to field water than to well water and onlyAe. albopictus oriented more to larval water or hay infusion than well water. In general, gravidAe. albopictus responded more strongly to oviposition stimuli than didAe. aegypti.

title: Role of Bacteria in Mediating the Oviposition Responses of Aedes albopictus (Diptera: Culicidae)
abstract: The responses of Aedes albopictus to sources of oviposition attractants and stimulants were evaluated with a behavioral bioassay in which females attracted to odorants emanating from water were trapped on screens coated with an adhesive. Gravid mosquitoes were attracted to volatiles from larval-rearing water and soil-contaminated cotton towels. Bacteria were isolated from these substrates and from an organic infusion made with oak leaves. Through fatty acid-methyl ester analyses, six bacterial isolates from larval-rearing water, two isolates from soil-contaminated cotton towels, and three isolates from oak leaf infusion were identified to species. The response of gravid mosquitoes to these isolates was also evaluated in behavioral bioassays. Water containing Psychrobacter immobilis (from larval-rearing water), Sphingobacterium multivorum (from soil-contaminated cotton towels), and an undetermined Bacillus species (from oak leaf infusion) elicited significantly higher oviposition than control water without bacteria. Only volatiles collected from larval rearing water elicited significant electroantennogram responses in females.

title: Chemicals of Predatory Mosquitofish (Gambusia affinis) Influence Selection of Oviposition Site by Culex Mosquitoes
abstract: Ovipositing insects may avoid aquatic sites where there is high predation risk to their offspring, but the proximate mechanisms that mediate avoidance behavior are poorly resolved. We conducted an experiment to determine whether mosquitoes would reduce oviposition rates in pools containing chemicals of the mosquitofish (Gambusia affinis), a voracious predator that is widely employed to control mosquitoes. Experimental treatments consisted of outdoor pools that contained known concentrations of fish chemicals (low, medium, or high) or no fish chemicals (control). The pools were arranged in a randomized block design, and the number of mosquito larvae in each pool served as the response variable to estimate relative oviposition rate. Members of the Culex pipiens complex were the main colonizers of the pools. The mean number of larvae per pool differed among treatments (P = 0.026) and was about three times greater in control pools compared with those receiving medium and high concentrations of fish chemicals. Pairwise comparisons indicate that only medium and high treatments differed significantly from controls, suggesting that a threshold concentration exists below which mosquitoes cannot reliably detect predators. Our data suggest that the effectiveness of Gambusia affinis in controlling mosquitoes may be compromised if adult mosquitoes respond to fish stocking by shifting to nearby breeding sites that lack fish. We discuss issues concerning the use of Gambusia in biological control programs within the context of these new findings.

title: Oviposition habitat selection in response to risk of predation in temporary pools: mode of detection and consistency across experimental venue
abstract: Natural selection should favor females that avoid ovipositing where risk of predation is high for their progeny. Despite the large consequences of such oviposition behavior for individual fitness, population dynamics, and community structure, relatively few studies have tested for this behavior. Moreover, these studies have rarely assessed the mode of detection of predators, compared responses in prey species that vary in vulnerability to predators, or tested for the behavior in natural habitats. In an outdoor artificial pool experiment, we tested the oviposition responses of two dipteran species, Culiseta longiareolata (mosquito) and Chironomus riparius (midge), to the hemipteran predator, Notonecta maculata. Both dipteran species have similar life history characteristics, but Culiseta longiareolata larvae are highly vulnerable to predation by Notonecta, while Chironomus riparius larvae are not. As their vulnerabilities would suggest, Culiseta longiareolata, but not Chironomus riparius, strongly avoided ovipositing in pools containing Notonecta. An experiment in natural rock pools assessing oviposition by Culiseta longiareolata in response to Notonecta maculata yielded an oviposition pattern highly consistent with that of the artificial pool experiment. We also demonstrated that the cue for oviposition avoidance by Culiseta longiareolata was a predator-released chemical: Notonecta water (without Notonecta replenishment) repelled oviposition for 8 days. Oviposition avoidance and mode of detection of the predator have important implications for how to assess the true impact of predators and for the use of commercially produced kairomones for mosquito control.

title: Effects of Pool Depth and Risk of Predation on Oviposition Habitat Selection by Temporary Pool Dipterans
abstract: Natural selection should favor females that oviposit in sites providing the best available conditions for her progeny. In temporary pools, two important conditions include risk of desiccation and risk of predation to larvae. In an artificial pool experiment, we compared oviposition responses of two dipterans, Culiseta longiareolata Macquart (Culicidae) and Chironomus riparius Meigan (Chironomidae), in very shallow pools that, if left to dry, would not have had a long enough hydroperiod for larvae to complete development, versus deeper pools that would have a sufficiently long enough hydroperiod for development. Water depth was crossed with the presence or absence of the predatory backswimmer Notonecta maculata F. (Hemiptera: Notonectidae). Oviposition patterns were consistent with larval vulnerability of the two species to predation by N. maculata. C. longiareolata, whose larvae are highly vulnerable to predation, strongly avoided ovipositing in pools containing this predator, whereas C. riparius, whose larvae are considerably less vulnerable, did not display oviposition avoidance. Pool depth did not affect oviposition habitat selection in either dipteran.

title: Melanotaenia duboulayi Influence Oviposition Site Selection by Culex annulirostris (Diptera: Culicidae) and Aedes notoscriptus (Diptera: Culicidae) but Not Culex quinquefasciatus (Diptera: Culicidae)
abstract: Some species of mosquito can detect the presence of larvivorous fish and select against ovipositing in pools supporting them. The effect of kairomones released by the crimson-spotted rainbowfish Melanotaenia duboulayi (Castelnau) on the oviposition behavior of the freshwater mosquitoes Culex annulirostris Skuse, Culex quinquefasciatus Say, and Aedes notoscriptus Skuse was evaluated in both laboratory and outdoor artificial pool experiments. In the laboratory, colony-reared Cx. annulirostris selected against ovipositing in water that had contained M. duboulayi at densities of one fish per 5, 30, 180, and 1,080 liters. In contrast, gravid Ae. notoscriptus showed a preference for water that had contained the highest density of M. duboulayi (1 in 5 liters). Gravid Cx. quinquefasciatus were neither repelled nor attracted to water that had previously contained M. duboulayi. In outdoor artificial pool experiments, wild Cx. annulirostris females selected against ovipositing in pools containing caged M. duboulayi stocked at rates of 1, 4, and 10 g per 1,000 liters. When fish were removed from the pools, the repellent effect persisted for at least 24 h, whereas at the lower stocking rate, an avoidance response was not noted until 48 h after fish were placed in pools. This suggests a volatile substance, however, the exact nature of the kairomone/s has not been identified.

title: Your worst enemy could be your best friend: predator contributions to invasion resistance and persistence of natives
abstract: Native predators are postulated to have an important role in biotic resistance of communities to invasion and community resilience. Effects of predators can be complex, and mechanisms by which predators affect invasion success and impact are understood for only a few well-studied communities. We tested experimentally whether a native predator limits an invasive species’ success and impact on a native competitor for a community of aquatic insect larvae in water-filled containers. The native mosquito Aedes triseriatus alone had no significant effect on abundance of the invasive mosquito Aedes albopictus. The native predatory midge Corethrella appendiculata, at low or high density, significantly reduced A. albopictus abundance. This effect was not caused by trait-mediated oviposition avoidance of containers with predators, but instead was a density-mediated effect caused by predator-induced mortality. The presence of this predator significantly reduced survivorship of the native species, but high predator density also significantly increased development rate of the native species when the invader was present, consistent with predator-mediated release from interspecific competition with the invader. Thus, a native predator can indirectly benefit its native prey when a superior competitor invades. This shows the importance of native predators as a component of biodiversity for both biotic resistance to invasion and resilience of a community perturbed by successful invasion.

title: Selective Oviposition by Aedes aegypti (Diptera: Culicidae) in Response to Mesocyclops longisetus (Copepoda: Cyclopoidea) Under Laboratory and Field Conditions
abstract: The influence of predacious Mesocyclops longisetus Thiebaud on the selection of oviposition sites by prey Aedes aegypti (L.) was studied under laboratory and field conditions. In both cases, gravid Ae. aegypti females were significantly more attracted to ovitraps containing copepods or to ovitraps with water in which copepods were held previously than to distilled water. Monoterpene and sesquiterpene compounds including 3-carene, α-terpinene, α-copaene, α-longipinene, α-cedrene, and δ-cadinene were found in hexane extracts of copepods by gas chromatography and mass spectrometry analyses. These compounds may be responsible for attracting gravid Ae. aegypti females and may increase the number of potential prey for the copepod.

title: Influence of nymphal Anax imperator (Odonata: Aeshnidae) on oviposition by the mosquito Culiseta longiareolata (Diptera: Culicidae) and community structure in temporary pools.
abstract: We assessed the overall (consumptive plus non-consumptive) and non-consumptive effects of nymphal Anax imperator (Aeshnidae: Odonata) on experimental pool communities by comparing three treatments: (1) control (no Anax); (2) free Anax (Anax was not constrained); and (3) caged Anax (Anax, enclosed within a cage, could not consume prey outside the cages, but could possibly influence them via perceived risk of predation). Fewer egg rafts of the mosquito Culiseta longiareolata were found in the free Anax treatment compared to the other two treatments. There was no statistically significant difference in the number of egg rafts between control and caged Anax pools. Thus, while Culiseta females apparently oviposit fewer egg rafts in the presence of unconstrained Anax, they did not respond to predation risk from the caged Anax. Larval Culiseta densities were drastically reduced by free Anax; there was nearly a 100% reduction in the number reaching metamorphosis (pupae) and a 100% reduction in emergence (pupal exuviae). There were no significant treatment effects on densities of crustaceans, Daphnia magna and Heterocypris sp., or on chironomid pupal exuviae. Ceratopogonid pupal abundance was higher in free Anax pools than in the other two treatments toward the end of the experiment. Free Anax caused a trophic cascade, presumably by strongly reducing the dominant periphyton grazer, Culiseta larvae; periphyton mass was greater in the free Anax treatment than in the control. However, there was no behavioral trophic cascade, i.e., no difference in periphyton abundance between the control and caged Anax treatment.

title: Ecology of invasive mosquitoes: effects on resident species and on human health.
abstract: Investigations of biological invasions focus on patterns and processes that are related to introduction, establishment, spread and impacts of introduced species. This review focuses on the ecological interactions operating during invasions by the most prominent group of insect vectors of disease, mosquitoes. First, we review characteristics of non-native mosquito species that have established viable populations, and those invasive species that have spread widely and had major impacts, testing whether biotic characteristics are associated with the transition from established non-native to invasive. Second, we review the roles of interspecific competition, apparent competition, predation, intraguild predation and climatic limitation as causes of impacts on residents or as barriers to invasion. We concentrate on the best-studied invasive mosquito, Aedes albopictus, evaluating the application of basic ecological theory to invasions by Aedes albopictus. We develop a model based on observations of Aedes albopictus for effects of resource competition and predation as barriers to invasion, evaluating which community and ecosystem characteristics favour invasion. Third, we evaluate the ways in which invasive mosquitoes have contributed to outbreaks of human and animal disease, considering specifically whether invasive mosquitoes create novel health threats, or modify disease transmission for existing pathogen-host systems.

title: Oviposition activity of Aedes aegypti L. (Diptera: Culicidae) in response to different organic infusions.
abstract: The present study investigates new sources of infusion as an oviposition attractant for Aedes aegypti L. Infusions with fetid and non-fetid odors were compared as an oviposition stimulant. Traps baited with infusions of dehydrated cashew leaves (Anacardium occidentale), potato peels (Solanum tuberosum) and graminea (Panicum maximum) were compared as attractants, and the effect of odor (fetid and unfetid) on attractiveness was tested. Oviposition activity changed significantly according to the concentration and type of infusion (F = 4.1279; gl = 2; P = 0.0231). A larger number of eggs were observed in cups containing 50% A. occidentale (non-fetid odor) and 30% P. maximum (fetid odor). When compared in the same cage, comparable oviposition was found between A. occidentale and P. maximum. Moreover, approximately 20% more eggs were recorded in the infusion without odor when compared to the grass infusion and water. These findings suggest A. occidentale as a new stimulant for use in ovitraps for Aedes surveillance and control, with the benefit of having an agreeable odor.

title: Aedes aegypti survival in the presence of Toxorhynchites violaceus (Diptera: Culicidae) fourth instar larvae
abstract: The mosquito Aedes aegypti (Linnaeus, 1762) is the main vector of dengue and yellow fever viruses. Different methods have been used to control A. aegypti, including chemical and biological tools. However, chemical control can lead to a subsequent increase in the mosquitoes' insecticide resistance, and biological control represents an important method as an alternative to insecticide usage. Larvae from the Toxorhynchites genus (Diptera: Culicidae) are predators of other mosquitoes and represent a potential natural biocontrol agent of A. aegypti larvae. In the present work, A. aegypti larval survival was studied in the presence of the neotropical Toxorhynchites violaceus (Wiedemann, 1821) fourth instar larvae. Toxorhynchites violaceus consumption of A. aegypti increased during the 192 hours of the experiment and was more marked in the intervals between 96 and 120 hours and between 168 and 192 hours, when the A. aegypti survival reached 0%. During the fourth instar, T. violaceus increased its predation on A. aegypti larvae, possibly in order to increase its nutrient storage prior to pupation. Otherwise, low prey consumption can lead to a nutritional deficit for the larvae, delaying the adult's sexual development and reducing its egg production. Here we show that A. aegypti survival can be reduced by the T. violaceus fourth larvae predation under laboratory conditions

title: Biological control of container‐breeding mosquitoes, Aedes albopictus and Culex quinquefasciatus, in a Japanese island by release of Toxorhynchites splendens adults
abstract: To control container‐breeding mosquitoes in the small island of Minnajima (0.56km2), northern Okinawa, Japan, laboratory‐reared adults (aged 7–10 days) of Toxorhynchites splendens (Palawan strain), a mosquito with predatory larvae, were released repeatedly during 1984, 1986 and 1987.

title: Egg‐laying Yellow Fever Mosquitoes avoid sites containing eggs laid by themselves or by conspecifics
abstract: Dave D. Chadee, ~ Philip S.  To whom correspondence should be addressed at Department of Zoology, University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, United Kingdom; 3 British Trust for Ornithology, Beech Grove, Station Road, Tring, Hertfordshire HP23 5NR, United Kingdom

title: Larval rearing water and preexisting eggs influence oviposition by Aedes aegypti and Ae. albopictus (Diptera: Culicidae).
abstract: Two-choice laboratory bioassays were used to evaluate oviposition responses of gravid Aedes aegypti (L.) and Ae. albopictus (Skuse) to larval rearing water and eggs from prior egg deposition. Oviposition responses by female Ae. aegypti were similar between larval water from Ae. aegypti and water controls but significantly greater to larval water from Ae. albopictus (12.2%) compared with water controls. Oviposition by Ae. albopictus females increased significantly in response to larval water from either species compared with water controls with increases of 15.1% to Ae. aegypti larval water and 17.6% to Ae. albopictus larval water. Oviposition responses of gravid Ae. aegypti and Ae. albopictus were evaluated in the presence of preexisting conspecific and heterospecific eggs on strips of oviposition paper. Significantly more eggs were laid by gravid Ae. aegypti females on oviposition paper containing either Ae. aegypti or Ae. albopictus eggs than on oviposition paper without eggs. In contrast, oviposition responses of gravid Ae. albopictus females were unaffected by the presence of eggs of either species.

title: Habitat selection determines abundance, richness and species composition of beetles in aquatic communities
abstract: Distribution and abundance patterns at the community and metacommunity scale can result from two distinct mechanisms. Random dispersal followed by non-random, site-specific mortality (species sorting) is the dominant paradigm in community ecology, while habitat selection provides an alternative, largely unexplored, mechanism with different demographic consequences. Rather than differential mortality, habitat selection involves redistribution of individuals among habitat patches based on perceived rather than realized fitness, with perceptions driven by past selection. In particular, habitat preferences based on species composition can create distinct patterns of positive and negative covariance among species, generating more complex linkages among communities than with random dispersal models. In our experiments, the mere presence of predatory fishes, in the absence of any mortality, reduced abundance and species richness of aquatic beetles by up to 80% in comparison with the results from fishless controls. Beetle species' shared habitat preferences generated distinct patterns of species richness, species composition and total abundance, matching large-scale field patterns previously ascribed to random dispersal and differential mortality. Our results indicate that landscape-level patterns of distribution and species diversity can be driven to a large extent by habitat selection behaviour, a critical, but largely overlooked, mechanism of community and metacommunity assembly.

title: Predation risk as a cost of reproduction.
abstract: Predation risk as a cost of reproduction in animals has recently received increased empirical and theoretical attention. Higher risk may be associated with all stages of reproduction. Examples of evolutionary responses to this increased risk include habitat choice, duration and timing of display and copulation, changes in brightness of breeding coloration, and changes in life history traits such as age of reproduction and reproductive effort.

title: MECHANISMS CREATING COMMUNITY STRUCTURE ACROSS A FRESHWATER HABITAT GRADIENT
abstract: ▪ Abstract Lentic freshwater habitats in temperate regions exist along a gradient from small ephemeral ponds to large permanent lakes. This environmental continuum is a useful axis for understanding how attributes of individuals ultimately generate structure at the level of the community. Community structure across the gradient is determined by both (a) physical factors, such as pond drying and winter anoxia, that limit the potential breadth of species distributions, and (b) biotic effects mediated by ecological interactions, principally predation, that determine the realized success of species. Fitness tradeoffs associated with a few critical traits of individuals often form the basis for species turnover along the gradient. Among species that inhabit temporary ponds, distributions are often constrained because traits that enhance developmental rate and competitive ability also increase susceptibility to predators. In permanent ponds, changes in the composition of major predators over the gradient limit ...

title: Identification of bacteria and bacteria-associated chemical cues that mediate oviposition site preferences by Aedes aegypti
abstract: The yellow fever mosquito, Aedes aegypti, the global vector of dengue and yellow fever, is inexorably linked to water-filled human-made containers for egg laying and production of progeny. Oviposition is stimulated by cues from water containers, but the nature and origin of these cues have not been elucidated. We showed that mosquito females directed most of their eggs to bamboo and white-oak leaf infusions, and only a small fraction of the eggs were laid in plain water containers. In binary choice assays, we demonstrated that microorganisms in leaf infusions produced oviposition-stimulating kairomones, and using a combination of bacterial culturing approaches, bioassay-guided fractionation of bacterial extracts, and chemical analyses, we now demonstrate that specific bacteria-associated carboxylic acids and methyl esters serve as potent oviposition stimulants for gravid Ae. aegypti. Elucidation of these compounds will improve understanding of the chemical basis of egg laying behavior of Ae. aegypti, and the kairomones will likely enhance the efficacy of surveillance and control programs for this disease vector of substantial global public health importance.

title: Chemical ecology and behavioral aspects of mosquito oviposition.
abstract: Etude du comportement de ponte dans la nature, de la selection du lieu de ponte, des attractifs et des stimulants de la ponte

title: Distributions of Competing Container Mosquitoes Depend on Detritus Types, Nutrient Ratios, and Food Availability
abstract: Coexistence of competitors may result if resources are sufficiently abundant to render competition unimportant, or if species differ in resource requirements. Detritus type has been shown to affect interspecific competitive outcomes between Aedes albopictus (Skuse) and Aedes aegypti (L.) larvae under controlled conditions. We assessed the relationships among spatial distributions of detritus types, nutrients, and aquatic larvae of these species in nature. We collected mosquitoes, water, and detritus from artificial containers across 24 Florida cemeteries that varied in relative abundances of Ae. aegypti and Ae. albopictus. We measured nutrient content of fine particulate organic matter in water samples as total N, P, and C and ratios of these nutrients. We quantified food availability via a bioassay, raising individual Aedes larvae in the laboratory in standard volumes of field-collected, particulate-containing water from each cemetery. Quantities of detritus types collected in standard containers were significant predictors of nutrients and nutrient ratios. Nutrient abundances were significant predictors of relative abundance of Ae. aegypti, and of larval survival and development by both species in the bioassay. Survival and development of larvae reared in particulate-containing water from sites decreased with decreasing relative abundance of Ae. aegypti. These data suggest that N, P, and C availabilities are determined by detritus inputs to containers and that these nutrients in turn determine the feeding environment encountered by larvae, the intensity of interspecific competition among larvae, and subsequent relative abundances of species at sites. Detritus inputs, nutrients, and food availability thus seem to contribute to distributions of Ae. aegypti and Ae. albopictus in cemetery containers throughout Florida.

title: The role of habitat selection behavior in population dynamics: source -sink systems and ecological traps
abstract: Ecological traps, poor-quality habitat that nonetheless attract individuals, have been observed in both natural and human-altered settings. Until recently, ecological traps were considered a kind of source--sink system, but source-sink theory does not model maladaptive habitat choice, and therefore cannot accurately represent ecological traps or predict their population-level consequences. Although recent models of ecological traps addressed this problem, they used patch-based models containing only two habitats that were very different from one another, but were internally homogeneous. These sorts of patch models may not apply to many real populations, and using them for populations in landscapes with mosaic or gradient habitat structures may be misleading. I developed models that treat source -sink dynamics and ecological traps as special cases of a single process, in which the attractiveness and quality of the habitat are separate variables that can be either positively or negatively related, and in which habitat quality varies continuously throughout the landscape. As expected, sinks are less detrimental to populations than ecological traps, in which preferential use of poor habitat elevates extinction risk. Furthermore, ecological traps may be undetected, and may even appear to be sources, when population sizes are large, but may still prevent recovery in spite of the availability of high-quality habitat when populations drop below threshold levels. Conservation biologists do not routinely consider the possibility that apparent sinks are actually traps, but since traps should be associated with the rapidly changing and novel habitat characteristics primarily produced by human activities, ecological traps should be considered an important and potentially widespread conservation concern.