A Survey of Aedes (Diptera: Culicidae) Mosquitoes in Tunisia and the Potential Role of Aedes detritus and Aedes caspius in the Transmission of Zika Virus.

The present study aimed to update the list of Aedes mosquito species occurring in Tunisia and to test the vector competence of Aedes (Ochlerotatus) caspius (Pallas) and Ae. (Ochlerotatus) detritus (Haliday), the locally most abundant and widespread species, to transmit Zika virus (ZIKV). In 2017-2018, mosquito larvae were collected from 39 different larval habitats in seven bioclimatic zones of Tunisia. The salinity and pH of each breeding site were measured. The survey revealed the presence of 10 Aedes species in Tunisia: Ae. (Stegomyia) albopictus (Skuse), Ae. (Ochlerotatus) berlandi (Séguy), Ae. caspius, Ae. detritus, Ae. (Finlaya) echinus (Edwards), Ae. (Finlaya) geniculatus (Olivier), Ae. (Acartomyia) mariae (Sergent and Sergent), Ae. (Ochlerotatus) pulcritarsis (Rondani), Ae. (Aedimorphus) vexans (Meigen), and Ae. (Fredwardsius) vittatus (Bigot). Of these 10 species, Ae. caspius and Ae. detritus were the most abundant in Tunisia. Aedes detritus and Ae. caspius larvae were reared until the imago stage under insectary conditions to test autogeny. The study showed that Ae. detritus is autogenous and stenogamous and Ae. caspius, anautogenous and eurygamous. Finally, the collected strains of these two species were experimentally infected with the Asian genotype of ZIKV, originally isolated from a patient in April 2014 in New Caledonia, to test their vector competence. Neither of these species was able to transmit ZIKV at 7 and 14 d postexposure. Further investigations are needed to test the competence of other Tunisian mosquito species that may be associated with ZIKV transmission.

Conditioning of Leaf Detritus Modulates Density-Dependent Growth of Aedes triseriatus Larvae (Diptera: Culicidae).

Ration of food per capita of larval population is widely thought to limit mosquito production from container habitats, directly reflecting resource limitation. In this study, the importance of density-dependent resource limitation on larval Aedes triseriatus (Say) (Diptera: Culicidae) depended on the degree of microbial conditioning of senescent leaf detritus in surrogate tree holes. Density and ration strongly affected emergence, total female mass, and mean female mass of populations grown on leaves that had conditioned for 3 d, but had less impact when larval populations were grown on leaves that had conditioned for 1 mo. Ration per capita was a stronger predictor (50-94% of the variance) of all growth parameters measured for populations grown on leaves conditioned for 3 d compared with 1 mo (2-66% of variance), with the exception of development time. Larvae grew faster and to a larger body size on leaves conditioned for 3 d at low densities of larvae and a higher ration per capita. However, populations grown on leaves conditioned for 1 mo produced equal or more total mass and individuals of higher average mass than when grown on leaves conditioned for 3 d in treatments with low ration per capita. Well-conditioned detritus, representing the degree of microbial colonization of the organic material, must reflect the typical condition in tree holes with unconditioned leaves atypical. Therefore, results of this study suggest that experiments using well-conditioned leaves better estimate growth responses, including moderated density dependence and less importance of ration per capita, than experiments using unconditioned detritus.

MOSQUITOES (DIPTERA: CULICIDAE) OF THE WESTERN COASTAL AREA, KINGDOM OF SAUDI ARABIA: SPECIES COMPOSITION, ABUNDANCE, DIVERSITY AND MEDICAL IMPORTANCE.

An entomological survey was undertaken for two years to update the mosquito fauna of the 3 regions (Mecca, Al Madinah and Tabouk), of the western coast, Kingdom of Saudi Arabia. Six localies representing such Regions (lhif, Mecca, Jeddah, Yanbu, Daba and Haql) were sampled for larvae and adults. Nineteen soecies of six genera were reported of which genus Culex (57.89% sp.) were the most commo6, followed by Anopheles (21.05%) and Stegomyia, Ochlerotatus, Aedes and Culesita (5.26% each). Three species (Cx. sitiens, Cx. torrenlium and Am. v. arabiensis) were new reports in study area. A total of 10930 larvae and 33108 adults were collected of which those representing genus Culex were predominating (92.74% larva, 93.46% adult). Of the reported species, Cx. quinquefasciatus (47.11% larva, 57.52% adult) and Cx. pipiens (22.24% larva, 27.42% adult) Were the common ones. Both Taif and Tabouk reported the highest number of species (13 sp., 68.42%), followed by Jeddah (12 sp., 63.16%), Mecca (10 sp., 52.63%) and Yanbu (8 sp., 42.11%). Tabouk represented the maximum diversity with the highest Simpson index (1-D=0.65) and Shannon index (H=1.25) followed by Taif (1- D=0.54, H=1.01). Per sampling site, Jeddah reported the highest number of larvae (313.70), and Mecca had the highest adult number (670.18). A complete list of mosquito fauna of the western coast including 35. spp. was presented based on the present and previous surveys. The role of the reported mosquito species as disease vectors was discussed. The study concluded that the diversity and abundance of the different mosquito species, among which several vectors of diseases mainly malaria, Rift Valley fever, lymphatic filariasis and dengue fever may pause a risk of transmission and more spread of such disease in this part that contains the holy places which are visited all year round by millions of people from several countries.

An overview of mosquitoes and emerging arboviral infections in the Zagreb area, Croatia.

Mosquito control in the Zagreb area has been conducted for many years, whereas the fauna has only been investigated in the last 20 years. So far 30 mosquito species have been detected in the city area. Culex pipiens form molestus is the dominant mosquito species in indoor breeding sites. In forested areas and areas exposed to flooding, the active period is early spring and the dominant species are Ochlerotatus sticticus, Ochlerotatus cantans, Ochlerotatus geniculatus and Aedes vexans. The eudominant mosquito species found in the artificial breeding sites are Culex pipiens and the Asian tiger mosquito, Aedes albopictus. Invasive Ae. albopictus, present in the Zagreb area since 2004, has expanded to a larger area of the city during the last three years. The recent emergence of the human West Nile virus and Usutu virus neuroinvasive disease in Zagreb and its surroundings highlighted the role of mosquitoes as vectors of emerging arboviruses. The paper focuses on mosquito species and arboviral infections detected in humans and animals in the Zagreb area, Croatia.

Bacterial Communities and Midgut Microbiota Associated with Mosquito Populations from Waste Tires in East-Central Illinois.

Mosquito-microbe interactions tend to influence larval nutrition, immunity, and development, as well as fitness and vectorial capacity of adults. Understanding the role of different bacterial species not only improves our knowledge of the physiological and ecological consequences of these interactions, but also provides the basis for developing novel strategies for controlling mosquito-borne diseases. We used culture-dependent and culture-independent techniques to characterize the bacterial composition and abundance in water and midgut samples of larval and adult females of Aedes japonicus (Theobald), Aedes triseriatus (Say), and Culex restuans (Theobald) collected from waste tires at two wooded study sites in Urbana, IL. The phylum-specific real-time quantitative polymerase chain reaction assay revealed a higher proportion of Actinobacteria and a lower proportion of gamma-Proteobacteria and Bacteroidetes in water samples and larval midguts compared to adult female midguts. Only 15 of the 57 bacterial species isolated in this study occurred in both study sites. The number of bacterial species was highest in water samples (28 species from Trelease Woods; 25 species from South Farms), intermediate in larval midguts (13 species from Ae. japonicus; 12 species from Ae. triseriatus; 8 species from Cx. restuans), and lowest in adult female midguts (2 species from Ae. japonicus; 3 species from Ae. triseriatus). These findings suggest that the composition and richness of bacterial communities varies both between habitats and among mosquito species and that the reduction in bacteria diversity during metamorphosis is more evident among bacteria detected using the culture-dependent method.

Container Type Influences the Relative Abundance, Body Size, and Susceptibility of Ochlerotatus triseriatus (Diptera: Culicidae) to La Crosse Virus.

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.

Impact of an Alien Invasive Shrub on Ecology of Native and Alien Invasive Mosquito Species (Diptera: Culicidae).

We examined how leaf litter of alien invasive honeysuckle (Lonicera maackii Rupr.) either alone or in combination with leaf litter of one of two native tree species, sugar maple (Acer saccharum Marshall) and northern red oak (Quercus rubra L.), affects the ecology of Culex restuans Theobald, Ochlerotatus triseriatus Say, and Ochlerotatus japonicus Theobald. Experimental mesocosms containing single species litter or a mixture of honeysuckle and one of two native tree species litter were established at South Farms and Trelease Woods study sites in Urbana, IL, and examined for their effect on 1) oviposition site selection by the three mosquito species, and 2) adult production and body size of Oc. triseriatus and Oc. japonicus. There were no significant effects of study site and leaf treatment on Oc. japonicus and Oc. triseriatus oviposition preference and adult production. In contrast, significantly more Cx. restuans eggs rafts were collected at South Farms relative to Trelease Woods and in honeysuckle litter relative to native tree species litter. Significantly larger adult females of Oc. japonicus and Oc. triseriatus were collected at South Farms relative to Trelease Woods and in honeysuckle litter relative to native tree species litter. Combining honeysuckle litter with native tree species litter had additive effects on Cx. restuans oviposition preference and Oc. japonicus and Oc. triseriatus body size, with the exception of honeysuckle and northern red oak litter combination, which had antagonistic effects on Oc. triseriatus body size. We conclude that input of honeysuckle litter into container aquatic habitats may alter the life history traits of vector mosquito species.

Thermal response in pre-imaginal biology of Ochlerotatus albifasciatus from two different climatic regions.

The biological processes on mosquito could be variable in response to local climatic characteristics. The thermal effects on time and the rate larval development, immature survival and adult size in local populations of Ochlerotatus albifasciatus (Macquart) (Diptera: Culicidae) from cold (Sarmiento) and temperate (Buenos Aires) regions from Argentina were evaluated. This species affects livestock production and human health. Larvae of both regions were placed in breeding thermal baths (11-32 °C range). Development and survival were recorded daily until adult emergence. The development temperature threshold and thermal constant for Sarmiento (4.59 ± 3.08 °C, 204.08 ± 7.83 degree days) was lower and higher than Buenos Aires, respectively (8.06 ± 1.81 °C, 149.25 ± 2.6 degree days). At cold temperatures (11-16 °C), Sarmiento larvae demonstrated 5 days faster development and higher survival (56%) than Buenos Aires (15%), whereas at warm temperatures (20-32 °C) were up to 2 days slower and similar survival (16% vs. 18%). The size did not show differences between populations. An Ochlerotatus albifasciatus population seems to present local thermal responses. The favourable temperature for survival and rate of development would vary within a cold or warm range, and these differential responses would explain the wide geographical distribution in different climatic regions of southern South America.

Species-specific non-physical interference competition among mosquito larvae.

Individuals of different sex, size or developmental stage can compete differently and hence contribute distinctively to population dynamics. In species with complex life cycles such as insects, competitive ability is often positively correlated with larval developmental stage. Yet, little is known on how the development and survival of early-instars is influenced by interference from late-instar larvae, especially at low densities when exploitative competition is expected to be negligible. Furthermore, the specificity and mechanisms by which interference competition operates are largely unknown. We performed two complementary experiments aiming to quantify the competitive effects of late instar Ochlerotatus caspius on early instar larvae at low densities and under high resource supply rate. The first experiment examined the net effect of interference by 4(th) on 1(st) instar O. caspius larvae, relative to the effect of 1(st) instars on themselves. The second experiment examined the effect of species-specific, non-physical interference competition (i.e., cage larvae) by 4(th) on 1(st) instar O. caspius larvae at low or high densities. Specifically, we compared the responses of O. caspius larvae raised in the presence of caged con- or hetero-specific, Culiseta longiareolata, with that of larvae in the empty-cage control group. As expected, interference from late instar larvae had a net negative effect on the development rate of first instars. In contrast, the presence of caged con-specifics (non-physical interference) accelerated the development rate of O. caspius, however, this pattern was only evident at the low density. Notably, no such pattern was detected in the presence of caged hetero-specifics. These results strongly suggest the existence of species-specific growth regulating semiochemicals.

Effects of Larval Density and Habitat Drying on Developmental Success of Ochlerotatus albifasciatus (Diptera: Culicidae) in Urban Rain Pools: Evidence From Field and Experimental Studies.

Ochlerotatus albifasciatus (Macquart) (Diptera: Culicidae) larvae develop synchronously after rainfall events in ephemeral or temporary pools, where they occasionally attain very high abundance. The aims of the current study were to analyze the response of life history parameters such as daily larval mortality, time to pupation, and adult size of Oc. albifasciatus to increasing larval density under controlled conditions, and to analyze the relationships of daily larval mortality with density and environmental variables (drying rate, temperature, and season) in urban rain pools in Buenos Aires, Argentina. An exponential increase in mortality was observed at high larval densities under controlled conditions. Development times and adult size (wing length) differed between males and females, and were also affected by density. Development times extended for 0.36 d for each order of magnitude of increase in larval density, and wing length decreased 0.0021 mm per additional larva in 600 cm(2). Larval density in the field varied from <1 larva per square meter to nearly 1100 larvae per square meter. Daily larval mortality values in the field were variable (0.02-0.91), positively related to the drying rate, and exhibited seasonal differences. No significant relation with larval density or temperature was found in the field. It remains to be established whether the density-independent mortality observed in this study is a generalized pattern of Oc. albifasciatus populations in Buenos Aires Province or a pattern restricted only to urban habitats.

Spatio-temporal patterns of distribution of West Nile virus vectors in eastern Piedmont Region, Italy.

BACKGROUND: West Nile Virus (WNV) transmission in Italy was first reported in 1998 as an equine outbreak near the swamps of Padule di Fucecchio, Tuscany. No other cases were identified during the following decade until 2008, when horse and human outbreaks were reported in Emilia Romagna, North Italy. Since then, WNV outbreaks have occurred annually, spreading from their initial northern foci throughout the country. Following the outbreak in 1998 the Italian public health authority defined a surveillance plan to detect WNV circulation in birds, horses and mosquitoes. By applying spatial statistical analysis (spatial point pattern analysis) and models (Bayesian GLMM models) to a longitudinal dataset on the abundance of the three putative WNV vectors [Ochlerotatus caspius (Pallas 1771), Culex pipiens (Linnaeus 1758) and Culex modestus (Ficalbi 1890)] in eastern Piedmont, we quantified their abundance and distribution in space and time and generated prediction maps outlining the areas with the highest vector productivity and potential for WNV introduction and amplification. RESULTS: The highest abundance and significant spatial clusters of Oc. caspius and Cx. modestus were in proximity to rice fields, and for Cx. pipiens, in proximity to highly populated urban areas. The GLMM model showed the importance of weather conditions and environmental factors in predicting mosquito abundance. Distance from the preferential breeding sites and elevation were negatively associated with the number of collected mosquitoes. The Normalized Difference Vegetation Index (NDVI) was positively correlated with mosquito abundance in rice fields (Oc. caspius and Cx. modestus). Based on the best models, we developed prediction maps for the year 2010 outlining the areas where high abundance of vectors could favour the introduction and amplification of WNV. CONCLUSIONS: Our findings provide useful information for surveillance activities aiming to identify locations where the potential for WNV introduction and local transmission are highest. Such information can be used by vector control offices to stratify control interventions in areas prone to the invasion of WNV and other mosquito-transmitted pathogens.

Identification and transcription profiling of trypsin in Aedes taeniorhynchus (Diptera: Culicidae): developmental regulation, blood feeding, and permethrin exposure.

The cDNA of a trypsin gene from Aedes (Ochlerotatus) taeniorhynchus (Weidemann) was cloned and sequenced. The full-length mRNA sequence (890 bp) for trypsin from Ae. taeniorhynchus (AetTryp1) was obtained, which encodes an open reading frame of 765 bp (i.e., 255 amino acids). To detect whether AetTryp is developmentally regulated, a quantitative real-time polymerase chain reaction was used to examine AetTrypl mRNA expression levels in different developmental stages of Ae. taeniorhynchus. AetTryp1 was expressed at low levels in egg, larval, and pupal stages, but was differentially expressed in adult Ae. taeniorhynchus, with highest levels found in 5-d-old female adults when compared with teneral adults. In addition, AetTryp1 mRNA expression differed between sexes, with expression levels much lower in males. However, in both males and females, there was a significant increase in AetTryp1 transcription levels as age increased and peaked in 5-d-old adults. AetTrypl expressed in 5-d-old female Ae. taeniorhynchus significantly increased after 30 min postblood feeding compared with the control. The AetTryp1 mRNA expression in 5-d-old female Ae. taeniorhynchus was affected by different concentrations of permethrin.

On the evolution of saline tolerance in the larvae of mosquitoes in the genus Ochlerotatus.

We examined physiological and morphological parameters associated with saline tolerance in the larvae of 11 species of mosquito in the genus Ochlerotatus that were collected from the wild in a variety of sites around North America. Saline tolerance was assayed, and all of the species were osmoregulators. Six of the species examined were found to be physiologically restricted to freshwater habitats, while the other five could successfully osmoregulate in both freshwater and saline water, including seawater. All larvae that were obligate freshwater forms had only one rectal segment, while all of the euryhaline osmoregulators had two. We were interested in the evolutionary pathway by which saline tolerance arose in this lineage. DNA sequence data were obtained by polymerase chain reaction amplification and sequencing of the D2 region of the 28s rDNA gene in all of the freshwater and saline-tolerant Ochlerotatus species we studied. When the morphological and physiological characters were mapped on the resultant cladogram, they revealed a complex pattern, with freshwater and saline-water forms being adjacent and interspersed through the tree. The data also demonstrate that saline tolerance has been gained and then lost at least once in this lineage. Two possible evolutionary scenarios are presented, but the one we favor is that saline tolerance arose one time in this lineage and repeated reversions to the freshwater condition have occurred.

Larvicidal activity of compounds isolated from Asarum heterotropoides against Culex pipiens pallens, Aedes aegypti, and Ochlerotatus togoi (Diptera: Culicidae).

The toxicity of several compounds isolated from Asarum heterotropoides root steam distillate to third-instar larvae of Culex pipiens pallens Coquillett, Aedes aegypti (L.), and Ochlerotatus togoi Theobald was examined using a direct contact mortality bioassay. Safrole was the most toxic constituent to Cx. p. pallens and Ae. aegypti larvae, whereas terpinolene was most toxic to Oc. togoi. However, LC50 values of these three mosquito larvae to both essential oils as well as the remainder of the 26 compounds identified in A. heterotropoides were considerably greater than for fenthion or temephos. However, we suggest that constituents of A. heterotropoides root steam distillate merit further study as potential mosquito larvicides due to global efforts to reduce the level of highly toxic synthetic pesticides in the aquatic environment.

First report of a North American invasive mosquito species Ochlerotatus atropalpus (Coquillett) in the Netherlands, 2009.

In late August and early September 2009, numerous larvae, pupae, and actively flying adult specimens of Ochlerotatus atropalpus were discovered in the Province of Brabant, southern Netherlands, during surveillance activities for Aedes albopictus at two trading companies that import used tires. No Ae. albopictus were found. Both companies mainly import used tires from countries in Europe, but also from North America. Oc. atropalpus is endemic to North America and has so far only been found outside of its endemic range in Europe, namely France and Italy, where it was subsequently eradicated. A preliminary modelling study shows that the weather conditions in the Netherlands are unlikely to prevent establishment of Oc. atropalpus. This species has so far only been shown to serve as a vector for virus transmission under laboratory conditions. Studies on potential human and veterinary health risks, as well as possible control strategies are currently ongoing.

Effect of diet composition on the development of the floodwater Mosquito Ochlerotatus (Ochletotatus) albifasciatus (Macquart) (Diptera: Culicidae) / Efecto de la composición de la dieta sobre el desarrollo del mosquito de inundación Ochlerotatus (Ochletotatus) albifasciatus (Macquart) (Diptera: Culicidae)

One important step for the colonization of Ochlerotatus albifasciatus (Macquart) is to determine the optimal conditions for larval rearing, which makes possible the development of experiments comprising larval rearing in the laboratory. In this research the effect of diet composition on the development of O.albifasciatus was studied. For this purpose, cohorts of 20 first instars were reared using five diets: 1:1 mix of yeast and TetraMin®, 1:1 mix of fine and coarse organic matter, grass cuts soaked in water for 1h or 24h before larvae incorporation, and 1:1:1 mix of grass cuts, fine organic matter and coarse organic matter. Survival was recorded for each cohort, while development time from first instar to pupa, and adult wing length were recorded for each individual. The effects of the diet on the observed traits were analyzed by one way ANOVA. Both survival and wing length were affected by diet, being significantly higher (79-100% and ~ 4.46 mm) on diets consisting of organic matter or organic matter plus grass than on those consisting of yeast plus TetraMin® or grass. Development time was not affected by the diet, although the shortest time (8.1 to 8.3 days) and lower variation between replicates were recorded when larvae were reared using organic matter or organic matter plus grass. Thus, it is concluded that the diets consisting of organic matter or a mix of it and grass are the most effective for O.albifasciatus rearing.

Un paso importante para la colonización de Ochlerotatus albifasciatus (Macquart) es conocer las condiciones óptimas para la cría de las larvas, lo cual además posibilita el desarrollo de experimentos en el laboratorio. En este trabajo se estudió el efecto de la dieta sobre el desarrollo de O. albifasciatus. Para ello se criaron cohortes de 20 larvas I utilizando cinco tipos de dietas: una mezcla 1:1 de levadura y TetraMin®, una mezcla 1:1 de materia orgánica fina y gruesa, gramíneas cortadas y sumergidas en agua 1h o 24h antes de incorporar las larvas, y una mezcla 1:1:1 de gramíneas cortadas, materia orgánica fina y materia orgánica gruesa. Para cada cohorte se registró la supervivencia, y para cada individuo, el tiempo de desarrollo desde larva I hasta pupa y la longitud del ala de los adultos. El efecto de la dieta sobre estas características se analizó mediante un ANOVA de una vía. Los resultados mostraron que la dieta afecta la supervivencia y la longitud del ala, obteniéndose los mayores valores de estas variables (79-100% y ~ 4,46 mm) con las dietas consistentes en materia orgánica o materia orgánica más gramíneas. El tiempo de desarrollo no estuvo afectado por la dieta, aunque el tiempo más corto (8,1-8,3 dias) y la menor variación entre réplicas se registraron al criar las larvas con materia orgánica o materia orgánica más gramíneas. Se concluye que las dietas consistentes en materia orgánica o una mezcla de ésta y gramíneas, son las más efectivas para la cría de O. albifasciatus.

Association of immature mosquitoes and predatory insects in urban rain pools.

Distribution among pools of six mosquito species and 23 predatory insect taxa were studied in temporary rain pools during the summer and fall season in Buenos Aires city. Both mosquito immatures and predators were disproportionally more abundant in pools with high flooded surface, depth, and duration. Mosquito immatures differed in their habitat use with respect to predators. Among mosquitoes, Ochlerotatus albifasciatus showed a different pattern when compared to the remaining culicids. More culicid and predatory insect taxa colonized the pools in those flooding events of longer duration. Ochlerotatus albifasciatus was the only mosquito species recorded during short duration events and the first one in colonizing the pools in long duration events. This species shared the pools mainly with early arriving adult predators. Three Culex species were recorded later and showed higher coexistence with most of the predatory taxa, mainly immatures of the genera Tropisternus, Rhantus, Liodessus, and Belostoma. A high heterogeneity between pools and seasons was observed. Multiple regression analyses showed a negative relationship of per capita change of Culex species with large-sized predators only in those cases where predators were collected in high abundances during the summer. No negative relationship of predators was detected in relation to per capita change and abundance of Ochlerotatus albifasciatus. Differences in duration of about two to three weeks seemed to significantly affect the abundance of both culicid and predatory taxa, suggesting that the urban pools analyzed in this study are on the extreme of suitable conditions for these aquatic insects.

Incorporating density dependence into the oviposition preference-offspring performance hypothesis.

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

Linking movement and oviposition behaviour to spatial population distribution in the tree hole mosquito Ochlerotatus triseriatus.

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.

Effect of diet composition on the development of the floodwater Mosquito Ochlerotatus (Ochletotatus) albifasciatus (Macquart) (Diptera: Culicidae).

One important step for the colonization of Ochlerotatus albifasciatus (Macquart) is to determine the optimal conditions for larval rearing, which makes possible the development of experiments comprising larval rearing in the laboratory. In this research the effect of diet composition on the development of O.albifasciatus was studied. For this purpose, cohorts of 20 first instars were reared using five diets: 1:1 mix of yeast and TetraMin(R), 1:1 mix of fine and coarse organic matter, grass cuts soaked in water for 1h or 24h before larvae incorporation, and 1:1:1 mix of grass cuts, fine organic matter and coarse organic matter. Survival was recorded for each cohort, while development time from first instar to pupa, and adult wing length were recorded for each individual. The effects of the diet on the observed traits were analyzed by one way ANOVA. Both survival and wing length were affected by diet, being significantly higher (79-100% and ~ 4.46 mm) on diets consisting of organic matter or organic matter plus grass than on those consisting of yeast plus TetraMin(R) or grass. Development time was not affected by the diet, although the shortest time (8.1 to 8.3 days) and lower variation between replicates were recorded when larvae were reared using organic matter or organic matter plus grass. Thus, it is concluded that the diets consisting of organic matter or a mix of it and grass are the most effective for O.albifasciatus rearing.