Mosquitoes Eating Mosquitoes: How Toxorhynchites amboinensis, Psorophora ciliata, and Sabethes cyaneus (Diptera: Culicidae) Capture Prey.

High-speed microcinematography was used to elucidate the details of prey capture by the larvae of three predatory mosquito species. The obligate predators Toxorhynchites amboinensis and Psorophora ciliata exhibited a high degree of convergence as both utilize three essential elements: 1) abdominally-generated hemostatic pressure to propel the head towards the prey; 2) lateral palatal brushes (LPB) opening and fanning into anterior-directed basket-like arrangements; 3) simultaneously with the LPB-basket formation, the wide opening of sharp-toothed mandibles. Thus, LPBs and mandibles are used for prey capture by both species. The facultative predator Sabethes cyaneus utilizes a vastly different prey-capture mechanism that involves ventro-lateral body arching and scooping of prey with axially pointed siphons into the grasp of open maxillae bearing elongate apical teeth. Prey consumption, which is typically incomplete in this species, then involves the action of teeth on the mandibles which cut into the held prey. Although prey consumption is incomplete, simple experiments show that Sa. cyaneus do gain nutritionally from consuming mosquito larvae and that they do discriminate heterospecific from conspecific larvae and actively approach heterospecific mosquito prey. These findings indicate that independent evolutionary pathways have produced diverse predatory behaviors and morphologies in aquatic environments where the immature stages of mosquitoes co-occur.

Experience- and age-mediated oviposition behaviour in the yellow fever mosquito Stegomyia aegypti (=Aedes aegypti).

In repeated behaviours such as those of feeding and reproduction, past experiences can inform future behaviour. By altering their behaviour in response to environmental stimuli, insects in highly variable landscapes can tailor their behaviour to their particular environment. In particular, female mosquitoes may benefit from plasticity in their choice of egg-laying site as these sites are often temporally variable and clustered. The opportunity to adapt egg-laying behaviour to past experience also exists for mosquito populations as females typically lay eggs multiple times throughout their lives. Whether experience and age affect egg-laying (or oviposition) behaviour in the mosquito Stegomyia aegypti (=Aedes aegypti) (Diptera: Culicidae) was assessed using a wind tunnel. Initially, gravid mosquitoes were provided with a cup containing either repellent or well water. After ovipositing in these cups, the mosquitoes were blood-fed and introduced into a wind tunnel. In this wind tunnel, an oviposition cup containing repellent was placed in the immediate vicinity of the gravid mosquitoes. A cup containing well water was placed at the opposite end of the tunnel so that if the females flew across the chamber, they encountered the well water cup, in which they readily laid eggs. Mosquitoes previously exposed to repellent cups became significantly more likely to later lay eggs in repellent cups, suggesting that previous experience with suboptimal oviposition sites informs mosquitoes of the characteristics of nearby oviposition sites. These results provide further evidence that mosquitoes modify behaviour in response to environmental information and are demonstrated in a vector species in which behavioural plasticity may be ecologically and epidemiologically meaningful.

The Effects of Interspecific Courtship on the Mating Success of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) Males.

Satyrization, a form of asymmetric reproductive interference, has recently been shown to play a role in competitive displacements of Aedes aegypti (L.) by Aedes albopictus (Skuse). Furthermore, female Ae. aegypti from populations in sympatry with Ae. albopictus have evolved reproductive character displacement and changes in mating behavior to reduce interspecific mating. In this article, we examine evolutionary responses of males to interspecific mating and show that satyrization has also evoked reproductive character displacement in males. We demonstrate that the presence of heterospecific females negatively influences conspecific mating success in male Ae. aegypti, most likely due to misdirected courting or mating efforts, and that males of this species from populations in sympatry with Ae. albopictus have evolved to be less influenced by the presence of heterospecific females than their allopatric counterparts. Conversely, we suggest that the presence of conspecifics may, in some circumstances, increase interspecific mating. This study demonstrates that co-occurrences of these two invasive species may lead to evolution and adaptation of reproductive behaviors to changing circumstances. Understanding the processes driving development of mate choice preferences or avoidance mechanisms may help predict future changes in the distribution and abundance of insect vectors or pests.

Spatial and temporal patterns of abundance of Aedes aegypti L. (Stegomyia aegypti) and Aedes albopictus (Skuse) [Stegomyia albopictus (Skuse)] in southern Florida.

Invasion by mosquito vectors of disease may impact the distribution of resident mosquitoes, resulting in novel patterns of vectors and concomitant risk for disease. One example of such an impact is the invasion by Aedes albopictus (Skuse) [Stegomyia albopictus (Skuse)] (Diptera: Culicidae) of North America and this species' interaction with Aedes aegypti L. (Stegomyia aegypti L). We hypothesized that Ae. aegypti would be found in urban, coastal areas that experience hotter and drier conditions, whereas Ae. albopictus would be more commonly found in suburban and rural areas that are cooler and wetter. In addition, we hypothesized that Ae. aegypti would be more abundant early in the wet season, whereas Ae. albopictus would be more abundant later in the wet season. Urban areas were drier, hotter and contained more Ae. aegypti than suburban or rural areas. Aedes aegypti was relatively more abundant early in the wet season, whereas Ae. albopictus was more abundant in both the late wet season and the dry season. The spatial patterns of inter- and intraspecific encounters between these species were also described. The distribution of these mosquitoes is correlated with abiotic conditions, and with temperature, humidity and the relative availability of rain-filled containers. Understanding the ecological determinants of species distribution can provide insight into the biology of these vectors and important information for their appropriate control.

Effects of combination of leaf resources on competition in container mosquito larvae.

Resource diversity is critical to fitness in many insect species, and may determine the coexistence of competitive species and the function of ecosystems. Plant material provides the nutritional base for numerous aquatic systems, yet the consequences of diversity of plant material have not been studied in aquatic container systems important for the production of mosquitoes. To address how diversity in leaf detritus affects container-inhabiting mosquitoes, we examined how leaf species affect competition between two container inhabiting mosquito larvae, Aedes aegypti and Aedes albopictus, that co-occur in many parts of the world. We tested the hypotheses that leaf species changes the outcome of intra- and interspecific competition between these mosquito species, and that combinations of leaf species affect competition in a manner not predictable based upon the response to each leaf species alone (i.e. the response to leaf combinations is non-additive). We find support for our first hypothesis that leaf species can affect competition, evidence that, in general, leaf combination alters competitive interactions, and no support that leaf combination impacts interspecific competition differently than intraspecific competition. We conclude that combinations of leaves increase mosquito production non-additively such that combinations of leaves act synergistically, in general, and result in higher total yield of adult mosquitoes in most cases, although certain leaf combinations for A. albopictus are antagonistic. We also conclude that leaf diversity does not have a different effect on interspecific competition between A. aegypti and A. albopictus, relative to intraspecific competition for each mosquito.

Food availability alters the effects of larval temperature on Aedes aegypti growth.

Variation in temperature and food availability in larval habitats can influence the abundance, body size, and vector competence of the mosquito Aedes aegypti. Although increased temperature has energetic costs for growing larvae, how food resources influence the developmental response of this mosquito species to thermal conditions is unknown. We explored how rearing temperature and food affect allometric scaling between wing size and epidermal cell size in Ae. aegypti. Mosquitoes were reared at 22 and 28 degrees C across a gradient of field-collected detritus designed to simulate commonly observed natural larval food resources. Overall, reduced temperature and increased food level increased wing size, but only temperature affected cell size. Females fed the least food had the longest time to maturation, and their increases in wing size induced by cold temperature were associated with larger, rather than more, cells. By contrast, males fed the most food had the shortest time to maturation, and their increases in wing size induced by cold temperature were associated with more, rather than larger, cells. Therefore, food levels can alter the underlying physiological mechanisms generating temperature-size patterns in mosquitoes, suggesting that the control of development is sensitive to the combination of nutrient and thermal conditions, rather than each independently. Conditions prolonging development time may favor increased cell division over growth. We suggest that understanding the effects of climate change on Ae. aegypti vectorial capacity requires an improved knowledge of how water temperature interacts with limited food resources and competition in aquatic container habitats.

Temperature induces trade-offs between development and starvation resistance in Aedes aegypti (L.) larvae.

Heightened temperature increases the development rate of mosquitoes. However, in Aedes aegypti (Diptera: Culicidae), the larvae of which commonly experience limited access to food in urban habitats, temperature effects on adult production may also be influenced by changes in the capacity of larvae to survive without food. We carried out experiments to investigate the effects of temperatures increasing at intervals of 2 °C from 20 °C to 30 °C on the growth, maturation rate and longevity of optimally fed larvae placed in starvation. Overall, both growth rate and starvation resistance were lower in the first three larval instars (L1-L3) compared with L4, in which growth of >75% occurred. Although increasing the temperature reduced the duration of each instar, it had a U-shaped impact in terms of the effect of initial growth on starvation resistance, which increased from L1 to L2 at 20 °C and 30 °C, remained constant at 22 °C and 28 °C, and decreased at 24 °C and 26 °C. Growth from L2 to L3 significantly increased starvation resistance only from 26 °C to 30 °C. Increased temperature (>22 °C) consistently reduced starvation resistance in L1. In L2-L4, increments of 2 °C decreased starvation resistance between 20 °C and 24 °C, but had weaker and instar-specific effects at >24 °C. These data show that starvation resistance in Ae. aegypti depends on both instar and temperature, indicating a trade-off between increased development rate and reduced starvation survival of early-instar larvae, particularly in the lower and middle temperatures of the dengue-endemic range of 20-30 °C. We suggest that anabolic and catabolic processes in larvae have distinct temperature dependencies, which may ultimately cause temperature to modify the density regulation of Ae. aegypti populations.

Distributions of Competing Container Mosquitoes Depend on Detritus Types, Nutrient Ratios, and Food Availability.

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

Retention and adaptiveness of photoperiodic EGG diapause in Florida populations of invasive Aedes albopictus.

Female Aedes albopictus, F2-F3 descendents from individuals collected as immatures at 6 geographic sites in the USA during 2008, exposed to short daylengths (10 h of light and 14 h of darkness at 21 degrees C) laid eggs in diapause, whose frequency depended upon population origin. Diapause responses in northern Florida and Illinois were strong, as had been reported approximately 10 years earlier for Ae. albopictus from these regions. For southern Florida, the diapause response was polymorphic, and its mean incidence decreased at 2 of 3 collection sites compared to 10 years earlier. Exposure in the field for 2- to 4-wk intervals in Vero Beach (lat 27 degrees 35'N) during January 2009 revealed that eggs laid by short-day females had significantly higher survivorship, even though <50% were estimated, from laboratory results, to be in diapause. Enhanced desiccation resistance may select for retention of diapause in southern Florida.

Differential Survivorship of Invasive Mosquito Species in South Florida Cemeteries: Do Site-Specific Microclimates Explain Patterns of Coexistence and Exclusion?

Within 2 yr of the arrival of the invasive container mosquito Aedes albopictus (Skuse), the previously dominant invasive mosquito Aedes aegypti (L.) disappeared from many Florida cemeteries. At some cemeteries, however, Ae. aegypti populations seem stable despite Ae. albopictus invasion. We sought to understand this variation in the outcome (exclusion, coexistence) of this invasion, given that previous experiments show that Ae. albopictus is the superior larval competitor. We tested experimentally the hypothesis that climate-dependent egg survivorship differs between exclusion and coexistence cemeteries and that differences in invasion outcome are associated with microclimate. Viability of eggs oviposited in the laboratory and suspended in vases at six cemeteries was significantly greater for Ae. aegypti than for Ae. albopictus, and greater in 2001 than in 2006. Cemeteries differed significantly in egg survivorship of Ae. albopictus, but not of Ae. aegypti, which is consistent with the hypothesis that Ae. albopictus suffers site-specific, climate-driven egg mortality that mitigates the competitive superiority of larval Ae. albopictus. Principal component (PC) analysis of microclimate records from vases during the experiments yielded three PCs accounting for >96% of the variance in both years of experiments. Multivariate analysis of variance of the three PCs revealed significant microclimate differences among the six cemeteries and between exclusion versus coexistence cemeteries. Stepwise logistic regression of egg survivorship versus microclimate PCs yielded significant fits for both species, and twice as much variance explained for Ae. albopictus as for Ae. aegypti in both years. Higher mortalities in 2006 were associated with high average daily maximum temperatures in vases, with lethal thresholds for both species at ≈40°C. From 1990 to 2007, vase occupancy by Ae. albopictus increased and that by Ae. aegypti decreased, with increasing seasonal precipitation at one well-sampled cemetery. Results support the hypothesis that locally variable climate-driven mortality of Ae. albopictus eggs contributes to patterns of exclusion of, or coexistence with, Ae. aegypti.

Interpopulation divergence in competitive interactions of the mosquito Aedes albopictus.

Geographic variation in species interactions can have major effects on distributions. Effects of such variation can be particularly evident for invasive species, in which variation in competitive ability can influence invasive success and impacts. We tested the hypothesis that coexistence or exclusion of the resident mosquito Aedes aegypti results from variation among local populations of the invasive Aedes albopictus in competitive interactions with A. aegypti. We also examined the role of variation in fecundity-size relationships in these competitive interactions. We compared competitive abilities of nine North American populations of A. albopictus, three populations from each of three site types: extinction of A. aegypti following A. albopictus invasion, coexistence following A. albopictus invasion, and A. albopictus allopatric to A. aegypti. Competition among larvae from each A. albopictus population and a single A. aegypti population was tested in laboratory microcosms in a response surface design. We found interpopulation differences in competitive ability of A. albopictus, but no strong patterns among site types. Extinction sites had steeper average fecundity-size relationships than coexistence sites and allopatric sites, but this did not translate into superior population performance. Certain individual A. albopictus populations had exceptionally large competitive effects on A. aegypti or poor competitive responses to competition from A. aegypti, but competitive effect and response were not correlated. These results suggest that interpopulation variation in the competitive ability of A. albopictus may only partly explain the geographic pattern of coexistence with or extinction of A. aegypti. Environmental differences among regions may affect the competitive ability of A. albopictus and influence its invasion success and impact.

Effects of intraspecific larval competition on adult longevity in the mosquitoes Aedes aegypti and Aedes albopictus.

Larval competition is common in container-breeding mosquitoes. The impact of competition on larval growth has been thoroughly examined and findings that larval competition can lead to density-dependent effects on adult body size have been documented. The effects of larval competition on adult longevity have been less well explored. The effects of intraspecific larval densities on the longevity of adults maintained under relatively harsh environmental conditions were tested in the laboratory by measuring the longevity of adult Aedes aegypti (L.) and Aedes albopictus (Skuse) (Diptera: Culicidae) that had been reared under a range of larval densities and subsequently maintained in high- or low-humidity regimes (85% or 35% relative humidity [RH], respectively) as adults. We found significant negative effects of competition on adult longevity in Ae. aegypti, but not in Ae. albopictus. Multivariate analysis of variance suggested that the negative effect of the larval environment on the longevity of Ae. aegypti adults was most strongly associated with increased development time and decreased wing length as adults. Understanding how larval competition affects adult longevity under a range of environmental conditions is important in establishing the relationship between models of mosquito population regulation and epidemiological models of vector-borne disease transmission.

Seasonal abundance of anopheline mosquitoes and their association with rainfall and malaria along the Matapí River, Amapá, [corrected] Brazil.

Three communities separated by 1.5-7.0 km, along the Matapí River, Amapá State, Brazil, were sampled monthly from April 2003 to November 2005 to determine relationships between seasonal abundance of host-seeking anophelines, rainfall and malaria cases. Out of the 759 821 adult female anophelines collected, Anopheles darlingi Root (Diptera: Culicidae) was the most abundant (56.2%) followed by An. marajoara Galvão & Damasceno (24.6%), An. nuneztovari Gabaldón (12.4%), An. intermedius (Chagas) (4.4%) and An. triannulatus (Neiva and Pinto) (2.3%). Vector abundance, as measured by human landing catches, fluctuated during the course of the study and varied in species-specific ways with seasonal patterns of rainfall. Anopheles darlingi and An. triannulatus were more abundant during the wet-dry transition period in June to August, whereas An. marajoara began to increase in abundance in February in two villages, and during the wet-dry transition in the other village. Anopheles nuneztovari and An. intermedius increased in abundance shortly after the rains began in January to February. A generalized linear mixed model (GLMM) analysis of 32 consecutive months of collections showed significant differences in abundance for each species by village and date (P < 0.0001). Correlations between lagged rainfall and abundances also differed among species. A strong positive correlation of An. darlingi abundance with rainfall lagged by 4 and 5 months (Pearson's r = 0.472-0.676) was consistent among villages and suggests that rainfall may predict vector abundance. Significant correlations were detected between numbers of malaria cases and abundances of suspected vector species. The present study shows how long-term field research may connect entomological and climatological correlates with malaria incidence.

Interspecific larval competition between Aedes albopictus and Aedes japonicus (Diptera: Culicidae) in northern Virginia.

Aedes albopictus (Skuse) and Aedes japonicus (Theobald) are two of the most recent and widespread invasive mosquito species to have become established in the United States. The two species co-occur in water-filled artificial containers, where crowding and limiting resources are likely to promote inter- or intraspecific larval competition. The performance of northern Virginia populations of Ae. japonicus and Ae. albopictus competing as larvae under field conditions was evaluated. Per capita rates of population increase for each species were estimated, and the effects of species composition and larval density were determined. In water-containing cups provided with oak leaves, Ae. albopictus larvae exhibited a competitive advantage over Ae. japonicus as a consequence of higher survivorship, shorter developmental time, and a significantly higher estimated population growth rate under conditions of interspecific competition. Intraspecific competition constrained population performance of Ae. albopictus significantly more than competition with Ae. japonicus. In the context of the Lotka-Volterra model of competition, these findings suggest competitive exclusion of Ae. japonicus in those habitats where this species co-occurs with Ae. albopictus.

Comparative Oviposition Site Selection in Containers by Aedes aegypti and Aedes albopictus (Diptera: Culicidae) from Florida.

Invasive container mosquito species Aedes aegypti (L.) and Ae. albopictus (Skuse) frequently co-occur in nature where they are typically segregated spatially by distinctive macrohabitat preferences that may select for different oviposition strategies. In a standard cage environment, we compared oviposition site selection by individual gravid females of these species exposed to variable numbers of water-holding cups and the presence or absence of a rugose wettable container lining. Offered plastic cups with and without lining, both species laid a significantly higher percentage of eggs in cups with lining (95.3% for Ae. aegypti, 88.4% for Ae. albopictus), than in cups without (4.7% for Ae. aegypti, 11.6% for Ae. albopictus). Linear regressions of container availability versus the number of lined cups colonized were similar for Ae. aegypti and Ae. albopictus. Rates of oviposition on the water surface differed by species for both cup types, with Ae. albopictus laying a higher percentage of eggs on the water surface in cups without lining (28.1% for Ae. aegypti, 51.3% for Ae. albopictus), than in cups with (5.3% for Ae. aegypti, 2.5% for Ae. albopictus). The more varied oviposition strategies of Ae. albopictus are interpreted in the context of its broader macrohabitat use and inferior egg desiccation resistance.

Widespread evidence for interspecific mating between Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in nature.

Aedes aegypti and Aedes albopictus, two important vectors of the dengue and chikungunya viruses to humans, often come in contact in their invasive ranges. In these circumstances, a number of factors are thought to influence their population dynamics, including resource competition among the larval stages, prevailing environmental conditions and reproductive interference in the form of satyrization. As the distribution and abundance of Ae. aegypti and Ae. albopictus have profound epidemiological implications, understanding the competitive interactions that influence these patterns in nature is important. While evidence for resource competition and environmental factors had been gathered from the field, the evidence for reproductive interference, though strongly inferred through laboratory trials, remained sparse (one small-scale field trial). In this paper we demonstrate that low rates (1.12-3.73%) of interspecific mating occur in nature among populations of these species that have co-existed sympatrically from 3 to 150yrs. Finally this report contributes a new species-specific primer set for identifying the paternity of sperm extracted from field collected specimens.

Long-term dynamics of a predator used for biological control and decoupling from mosquito prey in a subtropical treehole ecosystem.

We identified, staged and counted the immature stages of mosquitoes from 1,826 censuses (with replacement) of the aquatic contents of ten treeholes surveyed every 2 weeks between 1978 and 1993. These time series were used to examine the population dynamics and effect on prey of the predatory mosquito Toxorhynchites rutilus. The mean annual frequency of occurrence of T. rutilus ranged from 0.02 to 0.67 among holes, and no fourth instars were recovered during a 30-month dry period. Oviposition and pupation by this species were recorded in all months, but most commonly in the spring. Overwintering larvae of the predator increased in weight during the prolonged fourth instar that preceded pupation in the spring. Time series analyses showed that the presence of a fourth instar T. rutilus significantly reduced the abundances of late-stage Aedes triseriatus mosquitoes. Pupal numbers of this prey species were more negatively affected by T. rutilus than were numbers of fourth instar A. triseriatus. Long-term declines in mean annual abundance of A. triseriatus prey during 16 years of observations on two holes were not correlated with increases in the mean annual frequencies of T. rutilus. Local extinctions of the aquatic stages of A. triseriatus within treeholes were common, but in most holes not significantly associated with the presence of T. rutilus, suggesting that predation does not routinely drive mosquito prey locally extinct in this ecosystem. The decoupling of T. rutilus and A. triseriatus, as revealed through these complete and long-term censuses, is contrasted with other reports of generalist predators causing extinctions of mosquito prey. Discrepancies among reported outcomes probably result from differences in duration of sampling periods and statistical procedures along with real differences in the intensity of predation among systems and sites.

Fecundity, autogeny, and the larval environment of the pitcher-plant mosquito, Wyeomyia smithii.

Pupae and fourth instar larvae of a southern (30°N, Alabama, USA) population of Wyeomyia smithii Coq. (Diptera: Culicidae) were collected from pitcher plants. Adults which emerged were maintained without food then dissected to determine their egg clutch size. Among females which matured eggs, fecundities were negatively correlated with larval densities in individual pitchers. The mean autogenous fecundity of the overwintering generation did not differ from a summer sample. Adults unable to mature eggs comprised 6-39% of samples, depending on whether collected as pupae or fourth instar larvae. Fecundity was negatively correlated with time to adult eclosion among larvae maintained on unrenewed pitcher contents in the laboratory.Cohorts from this population were reared in artificial containers from egg hatch to adulthood at a single density and a superior or inferior diet. On the superior larval diet, all females survived to reproductive age, and all but one (>99%) produced eggs autogenously. On the inferior diet, survivorship to adult eclosion was significantly less, a high proportion of females died before reaching reproductive age, and only 19% of survivors matured eggs without blood. Protracted larval development induced by the inferior diet did not influence the probability of autogeny among females that survived to reproductive maturity.The relationship between larval environment and reproductive strategies is contrasted across the geographic range of W. smithii. Bloodfeeding occurs among southern populations where density dependent constraints on preimaginal growth are constantly severe. The loss of hematophagy among northern populations may have been facilitated by periods of density independent larval growth.

Life tables of Toxorhynchites rutilus (Diptera: Culicidae) in nature in southern Florida.

Stage-specific survivorship curves were constructed for the immature stages of a native, predatory mosquito, Toxorhynchites rutilus (Coquillet), by regular censuses in the summer and fall of water-holding treeholes and tires. Survival from egg to adult ranged from 1.8 to 5.6%, and survivorship patterns were significantly heterogeneous between seasons and container types. The probability of death was highest in the first and fourth larval instars. Rainfall and drought were relatively unimportant risk factors during this study, but the probabilities of disappearance of eggs and first and fourth instars were significantly higher in the presence of large conspecifics, suggesting that cannibalism is a major source of mortality.

Predation of Mansonia (Diptera: Culicidae) by native mosquitofish in southern Florida.

In experimental tanks and wading pools, the mosquitofish Gambusia holbrooki reduced densities of Mansonia larvae which, because of their attachment to the roots of aquatic plants, have been regarded previously as relatively impervious to predation. Exoskeletal remains of larval Mansonia were recovered from 43.5% of stomachs dissected from G. holbrooki, but not from Heterandria formosa (least killifish) collected from two undisturbed ponds covered with water lettuce (Pistia stratiotes L.). After 24 h in aquaria exposed to ambient light, predation by G. holbrooki reduced densities of Mansonia on water lettuce to one-third that of controls but in the dark, no significant differences were observed. In reduced light, densities of second- and fourth-instar Mansonia were reduced significantly after 1 wk of exposure to G. holbrooki. Video recordings of predation in aquaria revealed that G. holbrooki glean water lettuce roots to locate attached Mansonia and also capture free-swimming, dislodged larvae.