Predation by odonates depresses mosquito abundance in water-filled tree holes in Panama

In the lowland moist forest of Barro Colorado Island (BCI), Panama, larvae of four common species of odonates, a mosquito, and a tadpole are the major predators in water-filled tree holes. Mosquito larvae are their most common prey. Holes colonized naturally by predators and prey had lower densities of mosquitoes if odonates were present than if they were absent. Using artificial tree holes placed in the field, we tested the effects of odonates on their mosquito prey while controlling for the quantity and species of predator, hole volume, and nutrient input. In large and small holes with low nutrient input, odonates depressed the number of mosquitoes present and the number that survived to pupation. Increasing nutrient input (and consequently, mosquito abundance) to abnormally high levels dampened the effect of predation when odonates were relatively small. However, the predators grew faster with higher nutrients, and large larvae in all three genera reduced the number of mosquitoes surviving to pupation, even though the abundance of mosquito larvae remained high. Size-selective predation by the odonates is a likely explanation for this result; large mosquito larvae were less abundant in the predator treatment than in the controls. Because species assemblages were similar between natural and artificial tree holes, our results suggest that odonates are keystone species in tree holes on BCI, where they are the most common large predators. Received: 4 November 1996 / Accepted: 11 April 1997     

Inside‐container effects drive mosquito community structure in Brazilian Atlantic forest

Metacommunity theory is a convenient framework in which to investigate how local communities linked by dispersal influence patterns of species distribution and abundance across large spatial scales. For organisms with complex life cycles, such as mosquitoes, different pressures are expected to act on communities due to behavioral and ecological partitioning of life stages. Adult females select habitats for oviposition, and resulting offspring are confined to that habitat until reaching adult stages capable of flight; outside‐container effects (OCE) (i.e., spatial factors) are thus expected to act more strongly on species distributions as a function of adult dispersal capability, which should be limited by geographic distances between sites. However, larval community dynamics within a habitat are influenced by inside‐container effects (ICE), mainly interactions with conspecifics and heterospecifics (e.g., through effects of competition and predation). We used a field experiment in a mainland‐island scenario to assess whether environmental, spatial, and temporal factors influence mosquito prey and predator distributions and abundances across spatial scales: within‐site, between‐site, and mainland‐island. We also evaluated whether predator abundances inside containers play a stronger role in shaping mosquito prey community structure than do OCE (e.g., spatial and environmental factors). Temporal influence was more important for predators than for prey mosquito community structure, and the changes in prey mosquito species composition over time appear to be driven by changes in predator abundances. There was a negligible effect of spatial and environmental factors on mosquito community structure, and temporal effects on mosquito abundances and distributions appear to be driven by changes in abundance of the dominant predator, perhaps because ICE are stronger than OCE due to larval habitat restriction, or because adult dispersal is not limited at the chosen spatial scales.     

Your worst enemy could be your best friend: predator contributions to invasion resistance and persistence of natives

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.     

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.     

Predator-prey interactions and community structure: chironomids,mosquitoes and copepods in Heliconia imbricata (Musaceae)

Summary Evidence from both field observations and experimental work indicates that predation by larvae of a midge, Pentaneura n. sp. (Chironomidae), causes the low densities of mosquito larvae (Culicidae) found in the water filled bracts of Heliconia imbricata (Musaceae), microhabitats typically colonized by mosquitoes. This predation affects 2 species of mosquitoes, Wyeomyia pseudopecten, a resident species, and Trichoprosopon digitatum, a non-resident species. Predation keeps resident mosquito densities low while completely excluding the nonresident mosquito from the habitat. Both these effects of predation depend on the presence of an abundant alternative prey, an undescribed species of harpacticoid copepod found in the bracts. These copepod prey sustain chironomids when resident mosquito densities are low, permiting predator densities to remain high enough to exclude the non-resident mosquito. I discuss the evolutionary and ecological implications of predation structuring communities.     

Habitat complexity reduces prey vulnerability: An experimental analysis using aquatic insect predators and immature dipteran prey

The effects of alternative prey and structural complexity of habitat on the selection of mosquito larvae by aquatic insect predators were evaluated in the laboratory. The water bugs Anisops bouvieri, Diplonychus (= Sphaerodema) rusticus, and D. annulatus, and the odonate nymphs, Ceriagrion coromandelianum and Brachydiplax chalybea chalybea, selected mosquito larvae based on their abundance relative to chironomid larvae and on the levels of habitat complexity. The effect of one prey species on the other was asymmetrical, as indicated through prey selectivity values. Compared to open habitat, the presence of macrophytes reduced the vulnerability of mosquito larvae while the effect was reverse in the presence of sediments. When both sediment and macrophytes were present in habitats, all the predators except D. annulatus consumed more mosquito larvae than chironomid larvae. The clearance rate, an indicator of predatory efficiency, varied among the predator species and habitat types. The results suggest that the outcome of the interactions between insect predators and mosquito immatures was context-dependent and that it was mediated by the presence of alternative controphic species and the habitat complexity.     

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.

     

Survey of the Mosquitoes (Diptera: Culicidae) of Mayotte

A transversal survey of immature mosquitoes was conducted on Mayotte Island (France) in the Comoros Archipelago, western Indian Ocean, with the aim to inventory the Culicidae and to document inter-species relationships in different habitats. In total 420 habitats were sampled for larvae and/or pupae mosquitoes, resulting in more than 6,000 specimens. Forty species belonging to 15 genera were collected, with eight taxa integrated for the first time to the Mayotte mosquito list. The most frequently recorded species were Stegomyia aegypti, St. albopicta, Anopheles gambiae and Eretmapodites subsimplicipes, the first three species being known vectors of viruses and parasites transmitted to humans. Mean species richness in habitats ranged from 1.00 to 3.29, with notable differences between habitats. For example, water-filled axils of banana leaves, tree-holes and crab-holes had low species richness, while cut bamboo, water pools, abandoned tires and marsh and swamp water had notably higher species richness. Twenty-seven mosquito species belonging to 12 genera were routinely collected (in ≥20% of at least one type of larval habitat) suggesting that multiple species play a role in the biocenosis of these aquatic habitats. Multispecies association was observed in 52% of the habitats. The co-occurrence of up to six species belonging to five genera was recorded in a single habitat. The mosquitoes of Mayotte show notable biogeographical affinities to those of Madagascar, as compared to the African continent. These two potential source areas are nearly equidistant from Mayotte, which in turn indicates biased dispersal from east to west. Our findings suggest that with relatively short-term intensive sampling in different habitats, it is possible to approach exhaustive species inventories based on collection of larvae. Mayotte, with its modest elevation range and land surface, has a notable species richness of mosquitoes with 45 well-documented species belonging to 15 genera.     

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.     

No detectable role for predators mediating effects of aquatic habitat size and permanence on populations and communities of container‐dwelling mosquitoes

1. General theory from aquatic ecology predicts that smaller aquatic habitats have shorter hydroperiods favouring species that are better resource competitors and complete development quickly. Larger habitats are predicted to have longer hydroperiods enabling longer‐lived predators to persist. Habitats with long hydroperiods and predators are predicted to favour slower‐developing, predator‐resistant species, rather than competitive species. 2. In a field experiment, habitat size and hydroperiod were manipulated independently in water‐filled containers, to test these hypotheses about processes structuring aquatic communities. Human‐made containers were used that are dominated by mosquitoes that vary in desiccation resistance, competitive ability, and predation resistance. 3. Habitat size and drying had significant effects on abundances of larvae of the common species in these communities. There was sorting of species by habitat size and by drying, with species that are better competitors relatively more abundant in smaller, more ephemeral habitats, and predator‐resistant, slower‐developing species relatively more abundant in larger or permanently flooded habitats. There were no detectable effects of habitat size or drying on the dominant predator. 4. Habitat size and its interaction with drying affected inputs of eggs to containers. Habitat size also affected relative abundances of the two dominant species in the egg population. 5. Although habitat size and hydroperiod significantly affected composition of these communities, these impacts did not appear to be mediated through effects on predator abundance. Species‐specific differences in habitat size and drying regime preferences, and habitat‐dependent larval performance appear to be the main forces shaping these communities.     

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.     

Diving beetle assemblages of flooded wetlands in relation to time,wetland type and Bti-based mosquito control

We investigated the abundance and taxonomic composition of the aquatic predatory insect fauna, with focus on adult diving beetles (Coleoptera: Dytiscidae), in eight temporary flooded wet meadows and two alder swamps in the River Dalälven floodplains, central Sweden from 2002 to 2006. Diving beetles are generalist predators and often abundant in various waters, including temporary wetlands. In the River Dalälven floodplains, recurrent floods induce massive hatching of flood-water mosquitoes (Diptera: Culicidae), which constitute a superabundant patchy and irregular food resource for aquatic predatory insects. Our aims were (1) to characterize the assemblage of adult diving beetles occurring in the wetlands during floods in relation to time and wetland type and (2) to evaluate the effect on the aquatic predator assemblage of strongly reducing the abundance of a potential prey, flood-water mosquito larvae with Bacillus thuringiensis var. israelensis (Bti) during floods. We found diving beetles to be the dominating aquatic predatory insect taxa in all 10 wetlands. There was a difference in Dytiscidae species richness but not in diversity between wet meadows and alder swamps after rarefaction. The cluster analysis based on dytiscid species and abundances showed very high similarities between the wetlands. The variance component analysis was unable to distinguish any factor that could explain more than 7.4% of the variation in the dytiscid species assemblages. The only effect of Bti-treatment against flood-water mosquito larvae, potential food for the predatory dytiscids, was a slight increase in abundance of the medium-sized dytiscid species. Our results are in accordance with previous studies, suggesting that irregular and recurrent flood dynamic structure the dytiscid fauna more than food limitations and environmental factors.     

Can adults of the New Zealand mosquito Culex pervigilans (Bergorth) detect the presence of a key predator in larval habitats?

The influence of predators on mosquito populations may be direct through predation or indirect through sub‐lethal responses of adult mosquitoes in life history traits such as oviposition behavior. In New Zealand, the backswimmer, Anisops wakefieldi, is a common predator of mosquito larvae found in temporary and permanent water bodies. We predicted that the New Zealand native mosquito, Culex pervigilans, whose larvae are vulnerable to predation of Anisops, would likely avoid the containers with the presence of Anisops or its kairomone. We established temporary water containers without predators, free‐roaming predators, caged predators (which were unable to eat mosquitoes), or containers from which predators were removed immediately prior to the experiment (these containers would have remnant kairomones from the predators). Each treatment with Anisops had predator densities of one, three, or nine Anisops. Contrary to our predictions, when choosing oviposition habitats, Cx. pervigilans appeared to ignore the presence of free‐roaming Anisops, caged Anisops, and water with Anisops kairomone. We thus observed no significant differences between the numbers of egg rafts laid by Cx. pervigilans in the different predator treatments nor were the number of egg rafts significantly affected by the density of predators. Rather than the presence of predators, environmental factors including temperature, humidity, and pressure were significantly correlated with mosquito oviposition. These mosquitoes appeared to either ignore the presence of the predator, had no ability to detect the presence of predators, or perhaps the cues from Anisops predators were not sufficiently strong enough to alarm these mosquitoes. We argue that the mosquito has not evolved the ability to detect the presence of these predators while ovipositing.     

Effects of prey density, prey instar, and patch size on the development of the predatory mosquito, Toxorhynchites towadensis

Effects of prey density, prey instar, and patch size on the development of the predatory mosquito larva, Toxorhynchites towadensis, were investigated in the laboratory. Survivors of T. towadensis showed different developmental patterns in relation to prey age structure. All predatory larvae in containers with only second instar prey developed into the third instar. However, in several containers with fourth instar prey, mortality of predators was observed. During the third instar, no predatory larva died, but both prey density and prey instar significantly affected the survival of predators during their fourth instar. Large prey size promoted large predator adults, and predatory larvae which grew up in small surface containers responded by developing to large sizes than those in large containers. Larval developmental time of the predators differed in each treatment. During first and second instars, faster predator development was observed in containers with small surface areas and containing young prey individuals. However, when development was enhanced by the presence of old prey individuals, no surface effect was observed. The fastest predator development was observed with prey of mixed instars and high density. This study suggests that a small surface container containing prey of mixed instars and high density is suitable for development of predators.     

Lack of prey switching and strong preference for mosquito prey by a temporary pond specialist predator

1. The strengths of trophic interactions within ecosystems can be mediated by complex mechanisms that require elucidation if researchers are to understand and predict population- and community-level stabilities. Where multiple prey types co-occur, prey switching (i.e. frequency-dependent predation) by predators may facilitate low-density prey refuge effects which promote coexistence. On the other hand, lack of switching and strong preferences by predators can strongly suppress prey populations, which is especially important considering vector species such as mosquitoes. 2. The present study quantifies prey switching and preference patterns of the temporary pond specialist copepod Lovenula raynerae towards larvae of the medically important Culex pipiens mosquito complex in the presence of different proportions of alternative Daphnia pulex prey. Further, it examines whether prey switching and preferences are contingent on the sex of the predator. 3. Lovenula raynerae exhibited a lack of prey switching and strong preference for larval mosquito prey overall, irrespective of predator sex. Also, when larval mosquitoes were available in higher proportions over daphniids, the strength of this positive selectivity increased. There was very little low-density refuge for mosquitoes where they were rare. 4. Lack of prey switching and strong preferences towards mosquitoes by predatory paradiaptomid copepods may enhance population-level regulation of disease vector mosquitoes that exploit temporary pond-style habitats. Accordingly, the conservation and promotion of these predators might enable better management of medically important species across landscapes.     

Potential for integrated control of Culex quinquefasciatus (Diptera: Culicidae) using larvicides and guppies

Acute toxicity tests were carried out to determine the effect of three larvicides, spinosad, pirimiphos methyl, and chlorpyrifos, on Culex quinquefasciatus Say, Anopheles gambiae s.s. Giles (Diptera: Culicidae), and guppies, Poecilia reticulata Peters (Pisces: Poeciliidae). Thereafter, larvae of Cx. quinquefasciatus were introduced to P. reticulata in containers of different volumes with low concentrations of each larvicide at established predator to prey densities of 1–35; 5–70 and 10–350 (fish to larvae) respectively. The experiment was replicated six times, and the larval consumption was counted after 24 h. Spinosad and pirimiphos methyl were significantly toxic to Cx. quinquefasciatus, the less susceptible mosquito species. Guppy consumption of Culex larvae was highest at a predator to prey density 5–70. Feeding activity of guppies increased in the spinosad treatment at 49 μg L⁻¹ compared to control and the synthetic larvicides. The synthetic larvicides generally reduced consumption of larvae except for the lowest concentration of pirimiphos methyl which increased it at the highest predator to prey density in a 3 L container. The highest percentage of Culex larvae was consumed by fish in the presence of spinosad at 49 μg L⁻¹ and a predator to prey density of 5–70 in 0.5 L plastic containers. Thus, predator to prey density, container size, type and concentration of larvicide are all important factors to be considered in integrated management of mosquito larvae.     

Increasing isolation reduces predator:prey species richness ratios in aquatic food webs

The number of species that live in a habitat typically declines as that habitat becomes more isolated. However, the influence of habitat isolation on patterns of food web structure, in particular the ratio of predator to prey species richness, is less well understood. We placed aquatic mesocosms at varying distances from ponds that acted as sources of potential colonists; then we examined how isolation affected the ratio of predator:prey species richness in the communities that assembled. In the final sampling, a total of 21 species (12 prey and 9 predators) of insects, crustaceans, and amphibians had colonized the mesocosms. We found that total species richness, as well as the richness of predators and prey, declined with increasing isolation. However, predator richness declined more rapidly than prey richness with increasing isolation, which lead to decreasing predator:prey ratios. This result conflicts with prior demonstrations of invariant predator:prey ratios in freshwater communities.     

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.