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Ochlerotatus triseriatus (Say), the primary vector of La Crosse virus (LAC), develops in a variety of natural and artificial aquatic containers where it often co-occurs with larvae of other mosquito species. We conducted a field study at two woodlots (South Farms and Trelease Woods) in Urbana, IL, to examine how container type influences vector abundance, body size, and susceptibility to LAC. Mosquito pupae were collected from tree holes, plastic bins, and waste tires, and eclosing adults were identified to species morphologically. Oc. triseriatus and Ochlerotatus japonicus (Theobald) females were orally challenged with LAC and midgut infection rate, disseminated infection rate, and body titer were determined by reverse-transcriptase real-time PCR. Oc. triseriatus was the dominant species collected in tree holes while Oc. japonicus and Culex restuans (Theobald) were mostly dominant in artificial containers. Female Oc. triseriatus and Oc. japonicus collected from plastic bins were significantly larger than those collected from tree holes or waste tires. Oc. japonicus females from South Farms were also significantly larger than those from Trelease Woods. Oc. triseriatus females collected from plastic bins and waste tires were significantly more susceptible to LAC infection relative to females collected from tree holes. In addition, Oc. triseriatus females from waste tires had significantly higher LAC titer relative to Oc. triseriatus from tree holes. For each container type and study site, wing length was not correlated to infection or dissemination rates. These findings suggest that the container type in which Oc.triseriatus develop may contribute to the spatial and temporal dynamics of LAC transmission.

1. It was determined if the predatory midge Corethrella appendiculata Grabham imposes a fitness cost in a native mosquito, Ochlerotatus triseriatus Say, and an invasive mosquito, Aedes albopictus Skuse. The hypothesis that decreased activity of immature prey in the presence of predator cues is associated with life history costs through all life cycle stages was tested. 2. In experiment 1, individual larvae of O. triseriatus or A. albopictus were raised in the presence or absence of predation cues at two resource levels. Prey were video recorded to detect behavioural responses and to measure development time, size at emergence, and adult longevity. In experiment 2, prey populations were reared in similar environments and the frequency of predator cue additions was varied. 3. Only O. triseriatus reduced its activity in the presence of predation cues. Predation cues were associated with longer immature development times and shorter adult life spans in O. triseriatus, whereas in A. albopictus, the cues were associated with a larger size of emerging adults. 4. In the present study, it was found that behavioural modifications during the larval stage can affect mosquitoes through multiple stages of their complex life cycle. The species-specific behavioural differences are probably attributable to the longer evolutionary history O. triseriatus has with predators, relative to the invasive A. albopictus.

Following the discovery of the introduced mosquito, Ochlerotatus japonicus in western New Hampshire in 2000, a series of twelve used tire casings in southeastern New Hampshire was sampled, beginning in 2001, to study the occurrence of O. japonicus and its abundance over a five year period. Prior to 2003, Ochlerotatus triseriatus, a native species, was the numerically dominant mosquito species found in older water-filled tire casings. By 2004, O. japonicus had replaced O. triseriatus as the dominant mosquito species in this habitat, and by 2006 comprised 83% of the 2 species collected from the tires. Ochlerotatus japonicus has two larval population peaks annually in southeastern New Hampshire during the breeding season: mid-April to mid-May in spring, and early August to mid-September in mid-to late summer. Eggs continue to hatch and some larvae are present until freezing (ice over) occurs, usually in late October to early November. Ochlerotatus triseriatus has a single larval population peak from...

We investigated the bacterial community composition of tree holes in relation to the presence and absence of larvae of the mosquito Ochlerotatus triseriatus. Larvae were eliminated from a subset of natural tree holes with Bacillus thuringiensis serovar israelensis, and total bacterial numbers, slow- and fast-growing colony-forming units on minimal media, and 16S rRNA gene sequence data from water column and leaf material were obtained. Total bacterial counts did not change significantly with treatment; however, the number of slow-growing cultivable bacteria significantly increased in the absence of larvae. Sequence classifications and comparisons of sequence libraries using LIBSHUFF indicated that the elimination of larvae significantly altered bacterial community composition. Major groups apparently affected by larvae were Flavobacteriaceae, Rhodobacteraceae, Comamonadaceae, and Sphingomonadaceae. A clear dominance of Flavobacteriaceae in the water column after larval removal suggests members of this group are a major bacterial food source.

Insecticidal activity of eight plants collected from Burkina Faso was studied using mosquito ( Ochlerotatus triseriatus ), Helicoverpa zea and Heliothis virescens larvae and adult white fly ( Bemisia tabaci ). The n -hexane, ethyl acetate and methanol extracts of Pseudocedrela kotschyi , Strophantus hispidus , Securidaca longepedunculata , Sapium grahamii , Swartzia madagascariensis , Cassia nigricans , Jatropha curcas and Datura innoxia were used in this study. Extracts were tested at 250 μg/mL concentration. All three extracts of C. nigricans , J. curcas (skin and seeds) and D. innoxia exhibited 100% mortality on fourth instar mosquito ( O. triseriatus ) larvae. In addition, the n -hexane and ethyl acetate extracts of S. hispidus , S. longepedunculata , S. grahamii showed 100% mortality. The ethyl acetate extract of S. madagascariensis was the most active on adult white fly and exhibited 80% mortality. Extracts of all other plants exhibited 30–50% mortality on B. tabaci . In the antifeedant assays against H. zea and H. virescens , the MeOH extracts of C. nigricans , S. madagascarensis and S. hispidus were more effective against H. zea as indicated by 74% larval weight reduction as compared to the control. Since C. nigricans is commonly used in West Africa to protect grain storage from insects, we have characterized the insecticidal components present in its extract. Bioassay directed isolation of C. nigricans leaf extract yielded anthraquinones emodin, citreorosein, and emodic acid and a flavonoid, luteolin. Emodin, the most abundant and active anthraquinone in C. nigricans showed approximately 85% mortality on mosquito larvae Anopheles gambiaea and adult B. tabaci at 50 and 25 μg/mL, respectively, in 24 h. These results suggest that the extract of C. nigricans has the potential to be used as an organic approach to manage some of the agricultural pests.

Summary 1. Researchers often use the spatial distribution of insect offspring as a measure of adult oviposition preferences, and then make conclusions about the consequences of these preferences for population growth and the relationship between life-history traits (e.g. oviposition preference and offspring performance). However, several processes other than oviposition preference can generate spatial patterns of offspring density (e.g. dispersal limitations, spatially heterogeneous mortality rates). Incorrectly assuming that offspring distributions reflect oviposition preferences may therefore compromise our ability to understand the mechanisms determining population distributions and the relationship between life-history traits. 2. The purpose of this study was to perform an empirical study at the whole-system scale to examine the movement and oviposition behaviours of the eastern tree hole mosquito Ochlerotatus triseriatus (Say) and test the importance of these behaviours in determining population distribution relative to other mechanisms. 3. A mark‐release‐recapture experiment was performed to distinguish among the following alternative hypotheses that may explain a previously observed aggregated distribution of tree hole mosquito offspring: (H 1 ) mosquitoes prefer habitats with particular vegetation characteristics and these preferences determine the distribution of their offspring; (H 2 ) mosquitoes distribute their eggs randomly or evenly throughout their environment, but spatial differences in developmental success generate an aggregated pattern of larval density; (H 3 ) mosquitoes randomly colonize habitats, but have limited dispersal capability causing them to distribute offspring where founder populations were established; (H 4 ) wind or other environmental factors may lead to passive aggregation, or spatial heterogeneity in adult mortality (H 5 ), rather than dispersal, generates clumped offspring distributions. 4. Results indicate that the distribution of tree hole mosquito larvae is determined in part by adult habitat selection (H 1 ), but do not exclude additional effects from passive aggregation (H 4 ), or spatial patterns in adult mortality (H 5 ). 5. This research illustrates the importance of studying oviposition behaviour at the population scale to better evaluate its relative importance in determining population distribution and dynamics. Moreover, this study demonstrates the importance of linking behavioural and population dynamics for understanding evolutionary relationships among life-history traits (e.g. preference and offspring performance) and predicting when behaviour will be important in determining population phenomena.

Predator-mediated coexistence of competitors occurs when a species that is superior in competition is also more vulnerable to a shared predator compared to a poorer competitor. The invasive mosquito Aedes albopictus is usually competitively superior to Ochlerotatus triseriatus. Among second instar larvae, A. albopictus show a lesser degree of behavioral modification in response to water-borne cues from predation by the larval midge Corethrella appendiculata than do O. triseriatus, rendering A. albopictus more vulnerable to predation by C. appendiculata than O. triseriatus. The hypothesis that C. appendiculata predation favors coexistence of these competitors predicts that C. appendiculata abundances will be negatively and positively correlated with A. albopictus and O. triseriatus abundances, respectively, and that coexistence will occur where C. appendiculata are common. Actual abundances of O. triseriatus, A. albopictus, and C. appendiculata in three habitats fit this prediction. In natural container habitats like tree holes, C. appendiculata were abundant and competitors co-existed at similar densities. In cemeteries and tires, which occur primarily in non-forested, human-dominated habitats, A. albopictus dominated, with abundances twice those found in tree holes, but C. appendiculata and O. triseriatus were rare or absent. We also tested for whether antipredatory behavioral responses of A. albopictus differed among habitats or populations, or were correlated with local C. appendiculata abundances. We could detect no differences in A. albopictus antipredatory behavioral responses to water-borne cues from predation. Tree hole habitats appear to promote co-existence of O. triseriatus and A. albopictus through interactions with predatory C. appendiculata, and this predator effect appears to limit invasion success of A. albopictus in tree holes. There are many studies on predator-mediated coexistence in natural habitats but to our knowledge this is the first study to suggest differential predator-mediated coexistence between natural and man-made habitats.

Invasive arthropods that vector pathogens have the potential to influence pathogen transmission both directly, by becoming a novel pathogen vector, or indirectly, by interacting with native vectors. Adult mosquito size is influenced by food availability in the larval stage, and smaller, nutrient-deprived mosquitoes are, in some studies, more efficient viral vectors in the laboratory. This is the first study to examine the indirect impacts that larval competition between Aedes albopictus, an introduced mosquito species, and Ochlerotatus triseriatus, a native mosquito species and the primary vector for La Crosse virus (LACV) in the US, has on native mosquito larval survival, adult size, and vector competence. A. albopictus presence decreased Oc. triseriatus larval survival, but surviving Oc. triseriatus females were larger, potentially owing to a release from intraspecific competition. These larger, native females were more likely to develop both midgut and disseminated LACV infections than females emerging from monospecific treatments. Collectively, these results suggest a need to better understand the ecology of both native and invasive vector species, their interactions, and the potential for those interactions to alter vector-borne disease transmission.

1. The hypothesis that size-selective predation and species-specific prey behaviours facilitate the coexistence between larvae of invasive Aedes albopictus (Skuse) and U.S.A.-native Ochlerotatus triseriatus (Say) was tested experimentally with the predator Corethrella appendiculata (Grabham). 2. Larval behaviours associated with a higher risk of predation were identified, and prey behavioural responses were tested in either the physical presence of predators or in water containing predation cues. Larvae that thrashed on container bottoms had a higher risk of being captured by fourth instar C. appendiculata than did larvae resting on the water surface. Ochlerotatus triseriatus, but not A. albopictus, adopted low-risk behaviours in response to water-borne cues to predation. Both prey species reduced risky behaviours in the physical presence of the predator, but O. triseriatus showed a stronger response. 3. The vulnerability of 2nd and 3rd instar prey to predation was compared, and behavioural responses were correlated with prey vulnerability. Second instars of both species were more vulnerable to predation by C. appendiculata than were 3rd instars, and the 3rd instar A. albopictus was more vulnerable than O. triseriatus of the same stage. All instars of O. triseriatus showed a similar reduction of risky behaviours in response to the presence of C. appendiculata despite 4th instar prey being relatively invulnerable to size-selective predation. 4. Weaker predator avoidance, coupled with superior competitive ability, of invasive A. albopictus is likely to contribute to its coexistence with O. triseriatus in containers of the south-eastern U.S.A., where C. appendiculata can be abundant.

A total of 36,495 larvae consisting of 45 species from 11 genera were collected from 7,189 sites from southern New Jersey, Burlington County between the months of March and October, 2001-2014. Density and seasonal distribution were determined among natural and artificial habitat. The most dominant species collected from natural habitat was Aedes vexans (Meigen) followed by Ochlerotatus canadensis canadensis (Theobald), Culex restuans Theobald, Culex pipiens L., and Culex territans Walker. The most dominant species collected from artificial habitat was Aedes albopictus (Skuse) followed by Ochlerotatus japonicus japonicus (Theobald), Cx. restuans, Cx. pipiens, and Ochlerotatus triseriatus (Say). Cx. restuans and Cx. pipiens were the only species categorized as dominant among both natural and artificial habitat and comprised greater than half the total density. Sympatry was common among dominant species from artificial habitat where a significant percentage of the total collection contained multiple species. The most common types of natural habitats were forested depressions and stream flood plains whereas rimless vehicle tires and various plastic containers were the most common artificial habitats. The pitcher plant Sarracenia purpurea L. was the only habitat exclusive to one species.

A state-wide survey of tire-breeding mosquitoes in Alabama was conducted in 2004 and 2005. Tire sites in all 67 counties in the state of Alabama were sampled for mosquito larvae. A total of 13,022 mosquito larvae, representing 12 species in 7 genera, was collected. The most frequently collected species were Aedes albopictus (70.4%), Culex territans (8.0%), and Ochlerotatus triseriatus (7.1%). The following species were also collected: Cx. restuans (6.0%), Cx. salinarius (2.7%), Orthopodomyia signifera (2.4%), and Cx. quinquefasciatus (1.4%). Ochlerotatus atropalpus, Toxorhynchites rutilus, Anopheles punctipennis, An. quadrimaculatus, and Psorophora columbiae each represented

Eleven species of mosquito larvae were collected in 568 collection visits to 209 abandoned tire pile sites in 33 West Virginia counties from April through October of 2003. Ochlerotatus j. japonicus supplanted the native Oc. triseriatus as the most common tire-colonizing species in the state. In general, the exotic Oc. j. japonicus was a better colonizer of tires than Oc. triseriatus in peridomestic, sunlit conditions throughout the state, whereas both species were equally likely to colonize tires in nonperidomestic, shaded settings. Aedes albopictus competed effectively with Oc. triseriatus from mid-summer through October in low elevation western counties but was not well represented in central counties of the state. Aedes albopictus was seldom collected at higher elevations in eastern counties. Culex pipiens, like Ae. albopictus, was more likely to be in collections from the western portion of West Virginia throughout the study period. Frequency of occurrence of Cx. restuans peaked in early season collections and declined as the season progressed, but Anopheles punctipennis and the medically unimportant Cx. territans gradually increased in frequency each month through September. Typically, species in the genus Culex and An. punctipennis were predisposed to peridomestic, sunlit habitats. Larvae of the predatory Toxorhynchites rutilus septentrionalis were found mostly in nonperidomestic, shaded settings. This species initially appeared in mid-summer, and by August and September it was found in as many as 30% of the collection sites in western and eastern counties. Larvae of An. barberi, Oc. atropalpus, and Orthopodomyia signifera were poorly represented in collections.

We report 2 polymerase chain reaction (PCR)-based methods for distinguishing morphologically similar gregarine species based on amplification of variable regions of the internal transcribed spacer region of ribosomal DNA. The gregarines we investigated were Ascogregarina barretti (Vavra), A. culicis (Ross), and A. taiwanensis (Lien and Levine), parasites of the mosquitoes Ochlerotatus triseriatus (Say), Aedes aegypti (Linnaeus), and Ae. albopictus (Skuse), respectively. These 3 important vector mosquitoes often utilize the same container habitats, where larval development and infection by the parasite occurs, leaving ample opportunity for cross-species gregarine infection. Because previous studies have shown that the parasites A. culicis and A. taiwanensis variably affect fitness in both normal and abnormal mosquito hosts, distinguishing parasite infection and species is important. The task is complicated by the fact that these 2 parasite species are virtually identical in morphology, whereas A. barretti is morphologically distinct. Of the 2 PCR-based assays reported here, the first provides a rapid, sensitive, and straight- forward means of general ascogregarine detection based on a single PCR amplification. The second method provides a means of differentiation between A. culicis and A. taiwanensis based on a species-specific PCR assay. Together, these assays allow whole mosquitoes to be tested for the presence of Ascogregarina species as well as identification of both A. culicis and A. taiwanensis singly or in dual infections. Ascogregarina (Apicomplexa: Lecudinidae) contains a group of protozoan parasites that naturally infect certain insects. In mosquitoes (Diptera: Culicidae), infections have only been de- scribed from some container-breeding species (Beier and Craig, 1985). Three such species, Aedes aegypti (Linnaeus), Ae. al- bopictus (Skuse), and Ochlerotatus triseriatus(Say), are known or potential vectors of a number of arboviruses (Calisher, 1994). Each of the 3 mosquito species can naturally harbor a specific gregarine parasite that allows the host mosquito to carry out life functions relatively unaffected by its presence. The parasite is transmitted to other mosquitoes in the aquatic environment when feeding larvae ingest oocysts released by defecating or dead adult mosquitoes. Gregarine trophozoites feed intracellu- larly in the midgut epithelium and increase in size during mos- quito larval development; gametogony and sporogony in the Malphigian tubules during the pupal and early adult stages re- sult in new oocysts that are released back into the larval envi

Studies in aquatic systems have shown that habitat complexity may provide refuge or reduce the number of encounters prey have with actively searching predators. For ambush predators, habitat complexity may enhance or have no effect on predation rates because it conceals predators, reduces prey detection by predators, or visually impairs both predators and prey. We investigated the effects of habitat complexity and predation by the ambush predators Toxorhynchites rutilus and Corethrella appendiculata on their mosquito prey Aedes albopictus and Ochlerotatus triseriatus in container analogs of treeholes. As in other ambush predator-prey systems, habitat complexity did not alter the effects of T. rutilus or C. appendiculata whose presence decreased prey survivorship, shortened development time, and increased adult size compared to treatments where predators were absent. Faster growth and larger size were due to predator-mediated release from competition among surviving prey. Male and female prey survivorship were similar in the absence of predators, however when predators were present, survivorship of both prey species was skewed in favor of males. We conclude that habitat complexity is relatively unimportant in shaping predator-prey interactions in this treehole community, where predation risk differs between prey sexes.

1. The hypothesis that selective predation on larvae of the invasive Aedes albopictus (Skuse) could account for its stable coexistence with the native mosquito species and inferior competitor Ochlerotatus triseriatus (Say) in Florida treeholes and container systems was tested experimentally.2. Functional responses of the two dipteran predators Toxorhynchites rutilus (Coquillett) and Corethrella appendiculata (Grabham) were evaluated separately for A. albopictus and O. triseriatus prey. Both predators exhibited type II functional responses and consistently consumed more of the invasive species. Handling time of T. rutilus feeding upon O. triseriatus was significantly longer than when preying upon the invasive species.3. When either predator species was offered varying ratios of the two prey species, A. albopictus was consumed preferentially. The absence of a prey ratio effect on preference indicated that switching probably does not occur.4. The higher maximum feeding rate upon, and preference for, A. albopictus suggests that differential predation may foster coexistence of the invasive and native mosquito prey species in Florida.

I surveyed treeholes in central Pennsylvania for 7 mo in 1995 to investigate relationships among insect communities and water and leaf litter resources. I used water volume, essential to growth of treehole larvae, as an indicator of habitat size. Leaf litter is the basal food resource in treehole communities, and litter volume is related to the amount of energy available. Insect species richness and larval mosquito (Ochlerotatus triseriatus) and ceratopogonid midge (Culicoides guttipennis) densities were higher in treeholes that maintained high water volumes than those with low volumes throughout the study. Treeholes with high litter volume, irrespective of water volume, had the highest densities of C. guttipennis, and higher total larval densities than those with lower litter volumes; however, litter volume did not affect insect species richness. Scirtid beetle larvae were common in all treeholes, although their densities were unaffected by both litter and water volume. Insect species richness was not related to litter volume, unlike some other studies of phytotelmata. However, my study supported earlier conclusions that both habitat size and resource availability influence structure of treehole communities and maintain species populations. The influence of each resource on partic- ular species presence and density may be related to physical aspects of treeholes, biotic interactions, and natural history of individual species.

Larvae of the mosquito Toxorhynchites rutilus (Coquillett) prey upon other container-dwelling insects, including larvae of Aedes albopictus (Skuse), which is native to Asia but was introduced into the United States, and on the native tree hole mosquito Ochlerotatus triseriatus (Say). Previous work has established that O. triseriatus adopts low-risk behaviors in the presence of predation risk from T. rutilus. It is unknown whether introduced A. albopictus show a similar response to this predator. Behavior of fourth instars of A. albopictus or O. triseriatus was recorded in water that had held either A. albopictus or O. triseriatus larvae alone (control) and in water that had held T. rutilus larvae feeding on either A. albopictus or O. triseriatus (predation). Activity and position of larvae were recorded in 30-min instantaneous scan censuses. In response to water-borne cues to predation, O. triseriatus adopted low-risk behaviors (more resting, less feeding and movement), but A. albopictus did not change its behavior. We also tested the species specificity of the cues by recording the behavior of A. albopictus in water prepared using O. triseriatus and vice versa. O. triseriatus adopted low-risk behaviors even in predation water prepared by feeding T. rutilus with A. albopictus, but A. albopictus did not alter its behavior significantly between predation and control treatments prepared using O. triseriatus. Thus, A. albopictus does not seem to respond behaviorally to cues produced by this predator and may be more vulnerable to predation than is O. triseriatus.

Larvae of 12 mosquito species were collected from abandoned tire piles at peridomestic and forested sites in Nicholas County, WV, from March through November of 2001. No larvae were found in March, but the numbers of species increased to 10 by July and remained relatively constant, at 9-11 in any given month, throughout November. Larvae of Ochlerotatus triseriatus (Say), the most commonly encountered species in every month of collection, were significantly more likely to be found in forested tire pile sites. Conversely, Culex restuans Theobald, Anopheles punctipennis (Say), Cx. territans Walker, and Aedes albopictus (Skuse) larvae were significantly more likely to be found in peridomestic tire piles. Larvae of the remaining seven species were either found in equal proportions at peridomestic and woodland sites, or there were too few collections to make statistical inferences. Opportunities for competitive interactions between Ae. albopictus and Oc. triseriatus in Nicholas County would be minimized because the peak occurrence of the two species differ temporally and spatially.

When a species is introduced into a new location, it may escape, at least temporarily, from its natural enemies. In field surveys, we found that when the exotic, invasive mosquito, Aedes albopictus, invades new sites, it initially experiences reduced infection by its gut parasite, Ascogregarina taiwanensis. To determine the effect of this escape from parasitism on the competitive ability of A. albopictus, we performed a laboratory competition experiment in which infected and uninfected A. albopictus larvae were reared in microcosms alone and in competition with larvae of the native mosquito, Ochlerotatus triseriatus. We analyzed the effect of parasitism by A. taiwanensis on A. albopictus performance when subjected to intra- and interspecific competition across a range of larval densities, as well as the effect of A. albopictus parasitism by A. taiwanensis on the competitive impact of A. albopictus on O. triseriatus. At a density of 30 O. triseriatus larvae, O. triseriatus survivorship was significantly reduced by the addition of 30 unifected A. albopictus, but not by addition of 30 infected A. albopictus, and not by addition of 15 A. albopictus whether infected or uninfected. Although estimated finite rate of population increase (λ') showed similar trends, and was significantly affected by treatments, no pairwise differences in rate of increase were significant. Infection by A. taiwanensis also significantly prolonged A. albopictus female development time and reduced the intraspecific competitive effect of increased density of A. albopictus, but did not affect A. albopictus survivorship, mass, or estimated finite rate of population increase. Thus, when A. albopictus escapes from this parasite as it colonizes new sites, this escape may give it a small, but significant, added competitive advantage over O. triseriatus, which may facilitate range expansion of A. albopictus and enhance A. albopictus's initial impact on resident species.

Growth of larvae of the eastern tree-hole mosquito, Aedes triseriatus (Say), measured as survival to adulthood, development time, and body mass at adult emergence, was significantly better when larvae were provided with fresh rather than senescent beech leaves as food substrate. Leaf type affected larval growth performance independently of ration of leaf available per larva when the ration level was high and larvae were not densely crowded, but leaf type and ration level had interactive effects on larval growth performance when ration was more limiting and larvae denser. Fresh leaves contained about twice as much nitrogen, had a lower carbon:nitrogen ratio, leached more mass into water, and contained significantly more soluble protein and carbohydrate than did senescent leaves. Thus, the observed growth responses could be explained on the basis of variation in nutrient content of, and greater leaching from, the fresh leaves. Larval growth was also significantly better on intact senescent beech leaves than on leaves that had been leached to remove soluble protein and carbohydrate; it was also significantly better on leaves whose surfaces had flourishing bacterial growth than on leaves with disinfected surfaces. Growth of female larvae fit well a pupation window model where larvae attained a minimum mass to emergence past a minimum development time across a range of leaf substrates varying in quality and quantity.

Potential larval competition between Aedes albopictus (Skuse) and Aedes triseriatus (Say) was examined with replacement series experimental design, an analysis previously used to evaluate competition between plant species. Experimental design was a factorial treatment arrangement with four replications of larval diet (high and low) and species ratio (proportions of A. triseriatus/A. albopictus larvae 1:0, 3:1, 1:1, 1:3, and 0:1). Adult emergence, adult biomass, and sex ratio were evaluated. No competitive effects were observed in the high-diet treatments; however, significant competitive relationships were observed for all parameters in the low-diet treatments. Competition was evaluated by replacement diagrams, relative crowding coefficients, and analysis of variance. All techniques indicated that A. albopictus was a superior competitor to A. triseriatus under low diet. The use of the replacement series design was a powerful method for examining competition through a single experiment. The results indicate that replacement series experimental design can be used to characterize competition between animal species, providing that individual animals can be placed in an experimental habitat in appropriate proportions.

Mycobacterium ulcerans is the causative agent of Buruli ulcer, a severe necrotizing skin disease that causes significant morbidity in Africa and Australia. Person-to-person transmission of Buruli ulcer is rare. Throughout Africa and Australia infection is associated with residence near slow-moving or stagnant water bodies. Although M. ulcerans DNA has been detected in over 30 taxa of invertebrates, fish, water filtrate, and plant materials and one environmental isolate cultured from a water strider (Gerridae), the invertebrate taxa identified are not adapted to feed on humans, and the mode of transmission for Buruli ulcer remains an enigma. Recent epidemiological reports from Australia describing the presence of M. ulcerans DNA in adult mosquitoes have led to the hypothesis that mosquitoes play an important role in the transmission of M. ulcerans. In this study we have investigated the potential of mosquitoes to serve as biological or mechanical vectors or as environmental reservoirs for M. ulcerans . Here we show that Aedes aegypti , A. albopictus , Ochlerotatus triseriatus , and Culex restuans larvae readily ingest wild-type M. ulcerans , isogenic toxin-negative mutants, and Mycobacterium marinum isolates and remain infected throughout larval development. However, the infections are not carried over into the pupae or adult mosquitoes, suggesting an unlikely role for mosquitoes as biological vectors. By following M. ulcerans through a food chain consisting of primary (mosquito larvae), secondary (predatory mosquito larva from Toxorhynchites rutilus septentrionalis ), and tertiary ( Belostoma species) consumers, we have shown that M. ulcerans can be productively maintained in an aquatic food web.

In 2003, a survey at waste management grounds and tire dealerships was conducted to determine the species composition of mosquitoes in tires in southern Manitoba, Canada. Over 25% of the 1,142 tires sampled contained a total of 32,474 mosquito larvae and pupae. Culex restuans made up at least 95% of the larvae collected for each month of the summer. Culiseta inornata and Culex tarsalis reached their greatest numbers in July and August, respectively, though they were never abundant. Ochlerotatus triseriatus was also found but never reached more than 1% of the total larvae collected in any given month. Mosquito prevalence was more than three times greater in August (36.1%) than in June (11.7%). Orientation affected prevalence of mosquitoes in tires: 31.4% of vertical tires (tires standing on their treads) contained mosquitoes, whereas mosquitoes were found in only 18.9% of horizontal tires (tires parallel to the ground). Tires in the eastern region of Manitoba contained mosquitoes more often (61.7%), irrespective of date, than Winnipeg (25.9%), the central region (29.1%), or the western region (19.8%). Mosquito prevalence was similar across three size categories of tires, car tires (18.8%), truck tires (19.8%), and semi-trailer tires (26.7%), though tractor tires (47.8%) contained significantly more mosquitoes than tires in the other categories.

Discarded tires are an important habitat for larvae of multiple species of disease-transmitting mosquitoes. Although tire locations likely influence composition and abundance of vectors, there are few data linking vector populations to the characteristics of the aquatic tire environment. We sampled water-filled tires at three times at a forested and an unforested site to evaluate how differences in detritus inputs or nutrients in these two macrohabitats may be associated with composition of mosquito-dominated invertebrate communities. The forested site had significantly greater inputs of leaves, twigs, seeds, and fine detritus at the first sampling, but subsequent sampling indicated no differences in inputs of any detritus type. Total phosphorous levels were significantly greater in the forested site, but there was no difference in total nitrogen or total ion concentrations during any sampling. Chlorophyll a levels were not different between sites, even though light levels were greater and canopy cover was less at the unforested site. Culex restuans dominated at the unforested site, and Ochlerotatus triseriatus, Anopheles barberi, and Orthopodomyia signifera were found primarily in the forest. Tires at the forested site had significantly more species but not more individuals than at the unforested site. Leaf amount was a good predictor of densities of Oc. triseriatus and overall abundance of mosquitoes in the forest, whereas the amount of seeds was a good predictor of overall invertebrate richness and of Oc. triseriatus numbers in the unforested site. Differences in mosquito assemblage composition between forested and unforested locations may be explained by greater inputs of plant-based detritus and some nutrients, but other factors, such as macrohabitat or host preferences of adult mosquitoes, also may be important.

Investigations of competitive interactions emphasize non-detrital resources, even though detritus is a major component of most food webs. Studies of competing species focus usually on single resource types, although consumers in nature are likely to encounter mixtures of resource types that may affect whether competition results in exclusion or coexistence. The invasive mosquito Aedes albopictus is capable of excluding the native mosquito Ochlerotatus triseriatus in competition for single detritus types in laboratory and field microcosms. In this study, we used nine ratios of two detritus types (animal and leaf) common in natural containers to test whether detritus ratios affect the outcome of competition. Under intraspecific and interspecific competition, A. albopictus attained higher survival and estimated population growth rate than did O. triseriatus. Unlike past studies, both species had positive growth and high adult survival, with little evidence of competitive effects, under one resource ratio (10:1 ratio of leaf:animal detritus) regardless of mosquito densities, suggesting potential coexistence. Path analysis showed that densities of larvae had negative effects on population growth for O. triseriatus but not for A. albopictus, indicating competitive superiority of A. albopictus. Population growth of both species was affected strongly by the direct paths from animal (positive) and leaf (negative) detritus, and the indirect effect of leaf detritus via bacterial production (positive). Field sampling established that detritus entered real tree holes in ratios similar to those in our experiment, suggesting that natural variation in detritus ratios may influence local coexistence of these species. Seasonal variation in ratios of plant and animal detritus indicated that temporal as well as spatial variation in inputs may be important for potential coexistence. Keywords: aquatic microcosms, bacteria, density effects, mosquito, population growth Introduction Resource competition is an indirect negative interaction between species that occurs with the exploitation of shared, limiting resources. Theoretical and empirical work shows that competition of two species for one limiting resource results in competitive exclusion (Tilman 1982; Chase & Leibold 2003). Multiple mechanisms can result in competitive coexistence, including trade-offs between competitive ability and predator avoidance (Chase & Leibold 2003), dispersal ability (Levins & Culver 1971; Tilman 1994) or tolerances to abiotic variation (Chesson 1986; Chesson & Huntly 1997). Another prominent mechanism for coexistence is multiple resources, which can yield coexistence depending on resource ratios and inter-specific differences in use of resource types (Tilman 1982). Current theory surrounding food web dynamics and species interactions often focuses on direct or indirect manifestations of photosynthetic primary productivity (Moore et al. 2004), even though the majority of energy in food webs passes through detrital pathways (O’Neill & Reichle 1980; Moore et al. 2004). The effect of detritus on community attributes can be large. Detritus inputs can support higher diversity (Hairston & Hairston 1993) or can stabilize otherwise unstable energy fluxes and the dynamics of consumer populations more so than energy derived directly from primary productivity (Moore et al. 2004). Although there appear to be strong effects of detritus in many systems, few studies have investigated whether resource competition theory and predictions about resource ratios are accurate for detritus-based food webs. Mosquito larvae within detritus-based container systems (e.g. tree holes, bamboo stumps, discarded tyres) have proved to be useful model organisms for tests of hypotheses about processes structuring communities (e.g. predation: Lounibos, Nishimura & Escher 1993; Juliano & Gravel 2002; competition: Livdahl & Willey 1991; Juliano 1998; Teng & Apperson 2000). Natural containers (e.g. tree holes) are home to larvae of a variety of mosquito species, and interspecific competition can be strong (Kitching 2001). Tree holes are cavities in trees that receive inputs of terrestrial detritus, including senescent plant parts (primarily leaves, Kitching 2001), stem flow (water from precipitation flowing along tree trunks and containing organic matter, Carpenter 1982) and terrestrial invertebrate carcasses (Daugherty, Alto & Juliano 2000). Leaf inputs have variable effects on mosquito populations (Lounibos et al. 1993; Leonard & Juliano 1995; Walker et al. 1997; Juliano 1998), but animal-based detritus appears to have a greater effect on container mosquito performance (Yee & Juliano 2006) and can reduce the impact of competitive interactions (Barrera 1996; Daugherty et al. 2000). Mosquito larvae eat microorganisms growing on detritus surfaces (Merritt, Dadd & Walker 1992) and both animal and plant detritus support micro-organism growth (Yee & Juliano 2006). Because tree holes can contain different kinds of detritus resources, and these resources can affect performance of mosquitoes in different ways, we hypothesize that variation in the ratios of these detritus types will affect competitive coexistence of mosquitoes. We tested for the effect of different detritus ratios on the competitive outcome between two container mosquitoes, Aedes albopictus (Skuse) (Asian tiger mosquito) and Ochlerotatus triseriatus (Say) (eastern tree hole mosquito), (formally in the genus Aedes, Reinert 2000). A. albopictus was introduced into North America in the mid-1980s from Asia, and it now occurs across most of the southern United States (Hawley et al. 1987; Moore 1999). O. triseriatus is typically the dominant consumer in tree holes in the eastern United States (Bradshaw & Holzapfel 1985). Currently, A. albopictus and O. triseriatus overlap considerably in their large-scale distributions within the United States, and co-occur frequently (Lounibos et al. 2001; Aliabadi & Juliano 2002). A. albopictus has negative effects on resident mosquito species and has been shown to be superior to O. triseriatus in competition under field and realistic laboratory conditions (Livdahl & Willey 1991; Edgerly, Willey & Livdahl 1993; Teng & Apperson 2000). These competition experiments have used only leaf detritus as a resource. When raised on animal vs. plant detritus, O. triseriatus larvae grew significantly faster, adults were significantly larger and estimated population growth was significantly higher, suggesting that animal detritus is a higher quality food source (Yee & Juliano 2006). Daugherty et al. (2000) showed that animal and plant detritus could increase the likelihood of coexistence between A. albopictus and another mosquito, A. aegypti, although leaf-only treatments resulted in exclusion of A. aegypti. Whether the outcome of competition between A. albopictus and O. triseriatus is affected by animal detritus or by the ratios of plant and animal detritus is unknown. Livdahl & Willey (1991) suggested that A. albopictus would out-compete O. triseriatus in discarded automobile tyres, whereas coexistence would occur in natural tree holes, and speculated that tyres contained resources that were absent in tree holes and better exploited by A. albopictus, but did not consider that ratios of different kinds of detritus resources may differ between these container types. Variation in micro-organism productivity from different detritus types also could explain patterns of coexistence or exclusion, because mosquito larvae consume microorganisms exploiting detritus. Thus, the mechanism by which A. albopictus excludes or coexists with O. triseriatus remains unknown. We ask whether variation in the ratios of two detritus types could affect exclusion or coexistence between O. triseriatus and A. albopictus. We used nine ratios of two detritus types (leaves and invertebrate carcasses) in a factorial design with eight different combinations of densities of the two mosquitoes. We also quantified two measures of micro-organism activity (bacterial biomass production and metabolic rates) for each resource ratio, enabling us to quantify the direct food source for larvae. We used path analysis to determine the important direct and indirect casual links among detritus type, micro-organism productivity, mosquito densities and adult mosquito production and estimated population growth to test whether detritus ratios may be important for coexistence of A. albopictus and O. triseriatus. Finally, we measured detritus inputs into natural tree holes to characterize spatial and temporal patterns of these ratios in nature, and to infer whether exclusion or coexistence are likely under natural conditions.

Larvae of the eastern tree hole mosquito, Ochlerotatus triseriatus (Say), and related container-breeding species are known to feed upon substrate-associated microorganisms. Although the importance of these microbial resources to larval growth has been established, almost nothing is known about the taxonomic composition and dynamics of these critical microbial food sources. We examined bacterial and fungal community compositional changes on oak leaves tethered in natural tree hole habitats of O. triseriatus. We eliminated larvae experimentally in a subset of the tree holes and examined 16S rDNA gene sequences for bacteria and ergosterol concentrations and 18S rRNA gene sequences for fungi collected from leaf material subsamples. Leaf ergosterol content varied significantly with time, but not treatment. Principal component analysis (PCA) was used to compare microbial taxonomic patterns found in leaves incubated with or without larvae present, and we found that larval presence affected both bacterial and fungal groups, either from loosely attached or strongly adherent categories. Bacterial communities generally grouped more tightly when larvae were present, and class level taxa proportions changed when larvae were present, suggesting selection by larval feeding or activities for particular taxa such as members of the Bacteroidetes, Alphaproteobacteria, and Betaproteobacteria classes. Fungal taxa composite scores also separated along PC axes related to the presence of larvae and indicated larval feeding effects on several higher taxonomic groups, including Saccharomycetes, Dothideomycetes, and Chytridiomycota. These results support the hypothesis that larval mosquito feeding and activities altered microbial communities associated with substrate surfaces, potentially leading to decreased food value of the resource and affecting decomposition of particulate matter in the system.

Aquatic organisms often detect predators via water-borne chemical cues, and respond by showing reduced activity. Prey responses may be correlated with the concentration of predation cues, which would result in graded antipredator behavioral responses that adjust potentially costly behavioral changes to levels that are commensurate with the risk of predation. Larvae of the predatory mosquito Toxorhynchites rutilus prey upon other container-dwelling insects, including larvae of the mosquito Ochlerotatus triseriatus. Previous work has established that O. triseriatus reduce movement, foraging, and time below the surface, and increase the frequency of resting at the surface, in the presence of water-borne cues from predation by T. rutilus. We tested whether these responses by O. triseriatus are threat sensitive by recording behavior of fourth instar larvae in two runs of an experiment in which we created a series of concentrations (100, 10, 1, 0.1, and 0.01% and 100, 70, 40, 20, and 10%) of water that had held either O. triseriatus larvae alone (control) or a T. rutilus larva feeding on O. triseriatus (predation). We also tested whether associated effects on time spent feeding are threat sensitive by determining whether frequencies of filtering or browsing are also related to concentration of cues. The frequencies of resting and surface declined, whereas frequency of filtering (but not browsing) increased more rapidly with a decrease in concentration of predation cues compared with control cues. Thus, O. triseriatus shows a threat sensitive behavioral response to water-borne cues from this predator, adjusting its degree of behavioral response to the apparent risk of predation.

Ochlerotatus triseriatus is the natural vector of La Crosse virus, a common cause of pediatric encephalitis in the United States; the closely related Ochlerotatus hendersoni transmits this virus at low frequency. Adults of these mosquito species are difficult to distinguish morphologically; however, the larval stages show species-specific differences in several characters. We identified genomic regions contributing to the differences between the larvae of these species through interspecific hybridizations. Quantitative trait loci (QTL) were identified by standard interval mapping techniques and by univariate marker association analyses. We examined 159 F(2) progeny from an Oc. hendersoni female by Oc. triseriatus male interspecific cross for variation in the number of saddle and siphon hair branches, attachment of the acus, and morphology of the anal papillae. At least one putative QTL was identified for each of the phenotypes examined. QTL most commonly mapped to linkage group (LG) III, although QTL were identified on LGI and LGII for three phenotypes each. Several of these QTL, and particularly those on LGIII, also map to genome regions controlling adult female body size and ability to orally transmit La Crosse virus. Further studies are required to elucidate the relationships among these traits and the impact they may have had on the ecological specialization and speciation of these mosquitoes.

Effects of food, density, and heterospecific interactions on temperature-dependent development of Aedes albopictus (Skuse) and Aedes triseriatus (Say) larvae and pupae were described using a degree-day model. Under all conditions, the predicted number of degree-days (DD(T0)) to complete larval development was less, and the threshold temperature (T0) for initiation of larval development was higher for Ae. albopictus than for Ae. triseriatus. The DD(T0) for both species was food and density dependent. However, the per capita food ration appeared to exert a greater influence on the developmental times of Ae. triseriatus immatures, whereas for Ae. albopictus effects of density were not completely eliminated by an increase in the per capita food ration. The presence of heterospecific larvae did not prolong the DD(T0) of either species. At the low food ration, DD(T0) for both species were significantly greater under conspecific conditions. The DD(T0) for Ae. triseriatus increased directly as the proportion of conspecific larvae increased. However, when a higher per capita food ration was provided, conspecific effects on DD(T0) were mitigated. For Ae. albopictus, estimated DD(T0) values for larvae reared in pure culture were significantly higher than when heterospecific larvae were present, regardless of the per capita amount of food provided. Survivorship of immatures was density and food-dependent for both species. Ae. albopictus exhibited higher immature survivorship under all conditions relative to Ae. triseriatus. For both species, survival probabilities were lowest under conditions of high density and low food. Addition of food improved survival for both species. The presence of heterospecific larvae exerted a differential effect on the survivorship response of Ae. albopictus immatures to temperature. Lowest probability of survival for Ae. albopictus was occurred at low temperature when the proportion of heterospecific larvae in containers was the highest. In contrast, at high temperatures, survivorship of immatures improved, but was lowest for pure species cultures. For Ae. triseriatus, survivorship of immatures was consistently lower for pure species cultures regardless of the temperature. Standing crop production of adults of both species was primarily food rather that density-dependent. Under field conditions, Ae. triseriatus were predicted to initiate development sooner and exhibit faster population growth early in the season than Ae. albopictus. However, because of the shorter DD(T0), Ae. albopictus population growth was predicted to surpass that of Ae. triseriatus populations later in the season. Based on optimal DD(T0) values from laboratory experiments, spring emergence dates of Ae. triseriatus females in western North Carolina for 1989 and 1990 were predicted from accumulated degree-days calculated from local air temperature records. Predicted emergence dates were congruent with results of a previous survey for the same locality, indicating that accumulated degree-days can be used to accurately predict the seasonal occurrence of Ae. triseriatus. The utility of the degree-day approach in predicting the phenology of Ae. albopictus remains to be established.

The insect growth regulator (IGR) pyriproxyfen is highly active against mosquitoes (Diptera: Culicidae). Through continuous emersion of large larvae (instars 3–4) the concentration causing 50% inhibition of adult emergence (EI50) was determined as 0.200 p.p.b. for Aedes albopictus (Skuse) and 3.5 to 7 times less for Ochlerotatus triseriatus (Say): IE50 0.0288 p.p.b. As a possible method of application to larval microscosms of these species that oviposit in water containers and phytotelmata, the horizontal transfer of pyriproxyfen to larval microcosms by adult mosquitoes was evaluated under laboratory conditions. Gravid females were forced to walk on surfaces treated with pyriproxyfen (tarsal contact exposure) and then allowed to oviposit in larval microcosms. Using replicate bioassay cages, each with an oviposition container, and a factorial experimental design, we assessed Ae. albopictus for the effects of (i) pyriproxyfen concentration (0.2, 0.3 and 0.4 mg/cm2) contacted by gravid females, and (ii) the number of treated gravid females added to bioassay cages (one, three or five females/cage), on the mortality of larvae in oviposition containers. Only 0.2 mg/cm2 treatment rate was tested on Oc. triseriatus. A significant (P

Waste tires and other types of artificial containers were sampled for immature Aedes to monitor changes in the occurrence of Aedes aegypti (L.) and Aedes albopictus (Skuse) in Florida. The initial invasion and spread of Ae. albopictus in Florida occurred in the northern part of Florida. Throughout this region, major declines in the abundance of Ae. aegypti have been associated with the expansion of Ae. albopictus in both urban and rural areas. Generally, the same results have occurred in central Florida, but at some urban locations Ae. aegypti has remained a common mosquito long after the arrival of Ae. albopictus. In southeastern Florida, Ae. aegypti is currently the dominant container-inhabiting Aedes in urban areas, whereas sites dominated by Ae. albopictus are in rural settings or in undeveloped tracts of land within urban or suburban areas. At some locations, immature Ae. albopictus were found in the same containers with another exotic mosquito, Ae. bahamensis Berlin. The persistence of thriving Ae. aegypti populations in urban areas of southern Florida indicates that Ae. albopictus might not become the dominant container Aedes in these habitats, at least not to the extent that it has in the northern part of the state.

Container-inhabiting mosquito species are subject to both intraspecific and interspecific competition during larval development in resource-limited habitats. The arrival of an invasive species, Aedes albopictus, in the U.S. has altered competitive interactions among container-inhabiting mosquito species and, in some cases, has led to displacement of these species. Resource enrichment of container habitats has been shown to alleviate competitive interactions and to promote species co-existence; however, the importance of the timing of enrichment has yet to be explored. Larval competition between Ae. albopictus and a native species, Ochlerotatus triseriatus, was explored when resources were added either gradually or in a single pulse. Replacement series experiments revealed that Ae. albopictus was able to outcompete and displace Oc. triseriatus via resource monopolization when all resources were made available simultaneously; however, when the same resource amount was added over time, survival was high for both species, leading to co-existence. Timing of resource input also had an effect in monospecific treatments, indicating that intraspecific competition impacts survival as well. Duration of larval development was influenced by both species presence and by timing of resource input for Oc. triseriatus. These results indicate competitive outcome is condition-specific and that timing of resource input can determine whether a dominant invasive competitor displaces a native species, or if the two species are able to co-exist. Both intraspecific and interspecific competition occur at different temporal scales due to species-specific differences in larval developmental time. Timing of resource availability in container habitats can impact mosquito survival via competitive interactions, which can ultimately influence vector population size and behavior, possibly influencing vector-borne disease transmission.

Surveys for larval mosquitoes were conducted in West Virginia from 1992 through 1997. A total of 26 species were identified with the frequency of occurrence for each species determined by elevation category, month of collection and association with one or more of 15 defined larval habitat types (7 sunlit and 8 shaded). Larvae of Anopheles punctipennis, Culex restuans, Cx. territans and Ochlerotatus triseriatus (in rank order) were the most commonly encountered species. Anopheles punctipennis and Cx. territans were more likely to be found at low (

Leaves and flowers, the two main components of oak litter, were compared in the laboratory as growth substrates for larval Aedes triseriatus. Time to pupation was significantly faster and adult size significantly greater when flowers were the resource. Fitness, as measured by a composite index of performance (r'), was significantly higher among cohorts reared on flowers. A subsequent field experiment compared r' of cohorts developing in water-holding automobile tires, a common alternative habitat for treehole mosquitoes

We tested predictions of the hypothesis that behavioral differences are the proximate cause of interpopulation differences in vulnerability to predation in Aedes triseriatus. The predictions were : 1) A. triseriatus from sites where the predator Toxorhynchites rutilus is abundant vs rare differ in types of activities and positions occupied, or the degree to which they change behavior in the presence of T. rutilus; 2) Some activities or positions entail greater risks of predation than others; 3) High-risk behaviors are more common among larvae from sites where T. rutilus is rare vs sites where T. rutilus is common. Behavior was quantified by direct observation of individual larvae with T. rutilus present or absent. Riskiness of behaviors was quantified by recording the frequency with which different behaviors led to capture

Larvae of Aedes triseriatus mosquitoes feed on microbes that decompose leaf litter in tree—hole ecosystems. Scanning electron micrographs indicate that browsing by mosquitoes substantially reduces microbial abundance on decaying leaves. Experiments using laboratory microcosms demonstrate that increased larval density decreases larval survivorship, pupation rates, pupal biomass, and total yield. Rapidly decomposing leaf litter (sugar maple) supports more mosquito growth than slowly decomposing litter (beech and black oak). In our experiments, mosquito yield was apparently regulated by larval density and detrital dynamics. See full-text article at JSTOR

Mechanisms of larval population regulation in the detritivorous treehole mosquito Aedes triseriatus were explored experimentally, using laboratory microcosms of the treehole ecosystem. Quantity of beech leaf litter strongly limited growth, survivorship, and development rates of larvae. Little support was found for the hypothesis that an excreted substance causes density—dependent responses of larval A. triseriatus populations. Such an effect, if it exists, is much weaker than resource limitation. See full-text article at JSTOR

Interactions among the larvae of Aedes aegypti (L.), Ae. albopictus (Skuse), and Ae. triseriatus (Say) were studied in trispecific and bispecific mixed populations under laboratory and field conditions. Competitive stress (as evidenced by the average time to first, 50, and 75% pupation and the total pupation periods for mixed populations of each species in comparison with their single species controls) was more pronounced in mixed cultures reared in glass jars in the laboratory than in tires under field conditions. In the laboratory, the larval development of Ae. aegypti reared together with Ae. albopictus or Ae. triseriatus, or both, larvae was accelerated significantly. Conversely, the time to pupation for Ae. albopictus and Ae. triseriatus was delayed when reared with Ae. aegypti. However, the average wing length of female Ae. albopictus and Ae. triseriatus was greater in the mixed cultures than in single species cultures. These data indicated that the effect of intraspecific competition was greater than interspecific competition. Adequate food and higher temperature appeared to promote rapid development and higher survival of the immature stages of the three Aedes species in tires placed in the field. In general, Ae. triseriatus larvae required a longer period for larval development and had greater larval mortality than either Ae. aegypti or Ae. albopictus. In mixed populations of Ae, albopictus and Ae. aegypti in the jars and food-rich tires, the periods needed to attain first, 50, and 75% cumulative pupation were not significantly different than in single species controls. We conclude that no clear-cut displacement occurred in mixed experimental populations of Ae. aegypti and Ae. albopictus.

Aspects of population growth rates are examined for cohorts of the treeholes mosquito Aedes triseriatus, reared in field containers under different conditions of larval density, concentration of natural treehole fluid, and in the presence or absence of a late—hatching cohort of larvae. Density and fluid concentration produced similar and independent significant competitive effects on each measure of cohort success, including female mass, development time, and survival to the adult stage, as well as on a composite index of performance. The sensitivity of first—cohort development time to high density and dilute fluid was reduced by the presence of the second cohort, and first—cohort survivorship responses to fluid concentration and density suggest an enhanced performance in dilute medium and intermediate density due to the addition of the second cohort. A composite index did not detect these complex interactions of experimental factors, suggesting that overall population growth rates for the first cohort respond to density and food in a very simple manner. The second cohort experienced total mortality in the presence of high first—cohort density, dilute medium, or the incidental oviposition of another treehole mosquito, Anopheles barberi, and never matched the success of the first cohort, even under conditions of low density and concentrated fluid.