House sparrow uropygial gland secretions do not attract ornithophilic nor mammophilic mosquitoes.

Mosquito feeding preferences determine host-vector contact rates and represent a key factor in the transmission of vector-borne pathogens. The semiochemical compounds of which vertebrate odours are composed probably play a role in mosquito host choice. Birds spread secretions from uropygial gland over their feathers to protect their plumage, comprising behaviour that may in turn affect odour profiles. Although uropygial secretions are expected to modify the attractiveness of birds to mosquitoes, contradictory findings have been reported. Mosquito species differ in their feeding preferences, with some species feeding mainly on birds (ornithophilic species) and others on mammals (mammophilic species). Consequently, it is possible that ornithophilic and mammophilic species differ in their response to uropygial gland secretions. Using a dual-choice olfactometer, the present study tests this hypothesis by comparing the behavioural response to uropygial gland secretions from juvenile male and female house sparrows (Passer domesticus) in the ornithophilic Culex pipiens and the mammophilic Aedes (Ochlerotatus) caspius mosquitoes. No differences were found in the response of either mosquito species to the uropygial gland secretions. Therefore, the preference of ornithophilic mosquitoes for avian hosts is apparently not explained by a greater attraction of mosquitoes to the uropygial gland secretion odour when presented in combination with a CO2 -enriched airflow.

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.

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.

Evaluation of a temperate climate mosquito, Ochlerotatus detritus (=Aedes detritus), as a potential vector of Japanese encephalitis virus.

The U.K. has not yet experienced a confirmed outbreak of mosquito-borne virus transmission to people or livestock despite numerous autochthonous epizootic and human outbreaks of mosquito-borne diseases on the European mainland. Indeed, whether or not British mosquitoes are competent to transmit arboviruses has not been established. Therefore, the competence of a local (temperate) British mosquito species, Ochlerotatus detritus (=Aedes detritus) (Diptera: Culicidae) for transmission of a member of the genus Flavivirus, Japanese encephalitis virus (JEV) as a model for mosquito-borne virus transmission was assessed. The JEV competence in a laboratory strain of Culex quinquefasciatus (Diptera: Culicidae), a previously incriminated JEV vector, was also evaluated as a positive control. Ochlerotatus detritus adults were reared from field-collected juvenile stages. In oral infection bioassays, adult females developed disseminated infections and were able to transmit virus as determined by the isolation of virus in saliva secretions. When pooled at 7-21 days post-infection, 13% and 25% of O. detritus were able to transmit JEV when held at 23 °C and 28 °C, respectively. Similar results were obtained for C. quinquefasciatus. To our knowledge, this study is the first to demonstrate that a British mosquito species, O. detritus, is a potential vector of an exotic flavivirus.

Modeling of the putative distribution of the arbovirus vector Ochlerotatus japonicus japonicus (Diptera: Culicidae) in Germany.

Today, international travel and global freight transportation are increasing and have a direct influence on the introduction and establishment of non-native mosquito species as well as on the spread of arthropod (mosquito)-borne diseases inside Europe. One of the mosquito species that has become invasive in many areas is the Asian rock pool or bush mosquito Ochlerotatus japonicus japonicus (synonyms: Aedes japonicus japonicus or Hulecoeteomyia japonica japonica). This species was detected in Germany in 2008 for the first time. Until today, three different Oc. j. japonicus populations have been documented. Laboratory studies have shown that Oc. j. japonicus can act as a vector for a variety of disease agents. Thus, the knowledge on its current distribution is essential for different measurements. In the present study, ecological niche models were used to estimate the potential distribution of Oc. j. japonicus in Germany. The aim was to detect areas within Germany that could potentially function as habitats for this species. According to our model, areas in western, southern, and central Germany offer suitable conditions for the mosquito and may therefore be at risk for an invasion of the species. We strongly suggest that those areas should be monitored more intensively in the future. For this purpose, it would also be essential to search for possible dispersal routes as well as for natural barriers.

Effect of oral infection of La Crosse virus on survival and fecundity of native Ochlerotatus triseriatus and invasive Stegomyia albopicta.

Arboviruses can have benign, deleterious, or beneficial effects on the vector. We tested the hypothesis that oral infection with La Crosse virus (LACV) will have little to no effect on mosquito longevity and fecundity, a prediction of low virulence selected in a system with frequent vertical transmission. We tested the effects of infection in native Ochlerotatus triseriatus Say and invasive Stegomyia albopicta Skuse (Diptera: Culicidae). We artificially fed adult female mosquitoes of each species with either LACV-infected or uninfected bovine blood and determined adult longevity and fecundity. For females fed LACV-infected blood, bodies and legs, respectively, were separately homogenized and assayed by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) to determine the LACV infection and dissemination rates. Ochlerotatus triseriatus had a higher infection and dissemination rate than St. albopicta. For both species, female size had no effect on infection status. Infection status also had no effect on longevity or fecundity for both species. We suggest that the high frequency of vertical transmission may have selected for strains of the virus with low virulence in two vectors, in spite of their different evolutionary histories with the virus.

Evidence for reduction of native mosquitoes with increased expansion of invasive Ochlerotatus japonicus japonicus (Diptera: Culicidae) in the northeastern United States.

Ochlerotatus japonicus japonicus (Theobald) is an invasive mosquito native to Japan, Korea, and eastern China. The species was first detected in the northeastern United States in 1998 and has rapidly spread throughout much of eastern North America. In addition to used tire casings, Oc. j. japonicus develops in a wide variety of artificial and natural container habitats, especially rock pools along stream beds. In an effort to evaluate the invasion success and impact of Oc. j. japonicus on populations of native container dwelling species, waste tire disposal sites and natural rock pool habitats were sampled for mosquito larvae throughout Connecticut in 2005, and data were compared with results from prior surveys made in 1987 and 1999. Oc. j. japonicus was the predominant species collected at the waste tire disposal sites regardless of surrounding landscape features, accounting for 55.9% of all larvae. A comparison with collections from prior surveys revealed a 90% reduction in the relative abundance of larval populations of Oc. triseriatus (Say) and significant reductions among larval populations of Oc. atropalpus (Coquillett) and Culex restuans Theobald. Oc. j. japonicus was also the most abundant mosquito collected in rock pool habitats, accounting for nearly 80% of all collected larvae, except where water temperatures exceeded 30 degrees C. This was concomitant with significant declines in the relative abundance of Oc. atropalpus and Cx. restuans. We conclude that Oc. j. japonicus is a potentially effective competitor in rock pool and tire environments and may be responsible for reducing populations of several native species occupying these habitats through interspecific competition for limited resources. The exclusion of Oc. j. japonicus from warm water pools further suggests that a temperature barrier may exist for Oc. j. japonicus and that populations may not be able to colonize southern regions of the United States with relatively high summer temperatures.

Dispersal of the Mosquito Aedes vigilax (Diptera: Culicidae) From Urban Estuarine Wetlands in Sydney, Australia.

Aedes vigilax (Skuse) is a pest and vector species associated with coastal wetlands and the abundance of this mosquito has been identified as contributing to increased risk of mosquito-borne disease outbreaks. As urban development continues to encroach on these coastal wetlands, pest and public health impacts are becoming of increasing concern and in the absence of broadscale mosquito control. Urban planners are looking to buffer zones and other land use planning options to minimize contact between mosquitoes and humans but gaps in the understanding of dispersal ranges of mosquitoes hamper the adoption of these strategies. A mark-release-recapture experiment was conducted to measure the dispersal of this mosquito from an urban estuarine wetland in Sydney, Australia. An estimated total of over 150,000 wild caught female mosquitoes were marked with fluorescent dust and then released. A network of 38 traps was then operated for 5 d within an area of 28 km2. A total of 280 marked mosquitoes was recaptured, representing less than 1% of the estimate 250,000 marked mosquitoes released. Marked mosquitoes were recaptured up to 3 km from the release point, providing an insight into the dispersal range of these mosquitoes. The mean distance traveled by marked mosquitoes was 0.83 km, a result reflecting the greater proportion of marked mosquitoes recaptured near release point. The findings of this study indicate that effective buffer zones between estuarine wetlands and high-density urban developments would be an impractical approach to minimizing pest and public health impacts associated with this mosquito.

A Survey for Aedes aegypti in Delaware and the Virus-Positive Pool Rates of Aedes albopictus and Aedes triseriatus for West Nile and Zika Viruses.

The introduction of Zika virus to the USA in 2015 engendered heightened interest in its known vectors. Aedes aegypti is the primary vector, with Ae. albopictus considered a potential secondary vector, together with several other possible marginal vectors. In Delaware, Ae. aegypti has been collected rarely, but no breeding populations were detected during past intensive statewide surveillance efforts. However, there is an abundance of Ae. albopictus statewide. Both species are container breeders and are peri-domestic-increasing the risk for virus transmission to humans. From July through September 2017, Delaware Mosquito Control conducted surveillance in 16 container-breeding hot spots to search for Ae. aegypti, and also ascertain the virus-positive pool rates of Ae. albopictus and Ae. triseriatus for West Nile virus (WNV) and Zika virus (ZIKV). The survey concluded that there were no known breeding populations of Ae. aegypti in Delaware, and no WNV- or ZIKV-positive pools were detected among pools of mosquitoes of the aforementioned species.

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.

Update on the distribution of Ochlerotatus japonicus in Oregon and Washington.

In 2006, Ochlerotatus japonicus was found in Kelso, WA and Portland, OR. These are the southernmost collections of Oc. japonicus on the west coast of the USA. Though the methods of dispersal are not fully understood, it is evident that Oc. japonicus is expanding its distribution in the Pacific Northwest.

Wing morphometrics of Aedes (Ochlerotatus) albifasciatus (Macquart, 1838) (Diptera: Culicidae) from different climatic regions of Argentina.

BACKGROUND: Gene flow restrictions between populations of Aedes albifasciatus, the vector of Western equine encephalitis and Dirophilaria immitis, have been described in the central region of Argentina. Genetic and eco-physiological variations usually result in local forms reflecting the climatic regions. Mosquito wings and their different parts have ecological functions in flight and communication. Therefore, wing shape could be considered an aspect of sexual dimorphism, and its eco-physiological responses can be expressed as morphological changes induced by the environment. METHODS: To compare the geographical and sexual variations with respect to wing shape and size in two Ae. albifasciatus populations from contrasting climates of Argentina (temperate: Buenos Aires, and the arid steppe of Patagonia: Sarmiento), the wings of adults reared in thermal trays at different constant temperatures (10-29 °C) were analyzed. RESULTS: The wing size of Ae. albifasciatus showed inverse linear relationships with the rearing thermal condition and higher slope for Buenos Aires. In the cool range (10-17 °C), geographical size variations responded to the converse Bergmann's rule, where Buenos Aires individuals were larger than those from Sarmiento. Sexual shape dimorphism occurred in both populations while geographical variation in shape was observed in both sexes. CONCLUSIONS: Buenos Aires individuals showed greater response sensitivity with respect to the size-temperature relation than those from Sarmiento. The converse Bergmann's rule in size variation could be due to a higher development rate in Sarmiento to produce more cohorts in the limited favorable season. The shape could be more relevant with respect to the size in the study of population structures due to the size being more liable to vary due to changes in the environment. The geographical variations with respect to morphology could be favored by the isolation between populations and adaptations to the environmental conditions. Our results demonstrate that the shape and size of wing provide useful phenotypic information for studies related to sexual and environmental adaptations.

Establishment and abundance of a recently introduced mosquito species Ochlerotatus japonicus (Diptera: Culicidae) in the Southern Appalachians, USA.

Ochlerotatus (Finlaya) japonicus japonicus (Theobald; =Aedes japonicus; see Reinert 2000) (Diptera: Culicidae), is an introduced Asian mosquito species first detected in the northeastern United States in 1998. Since its initial discovery, this species has spread to many neighboring states and Canada. It was first identified in North Carolina, South Carolina, and Georgia in 2003. Larval surveys were conducted during 2005 and 2006 in the Southern Appalachians, U.S.A., on a variety of natural and artificial containers to determine extent of Oc.japonicus establishment and larval habitat requirements. Detritus amounts were measured in each container habitat, and co-occurring larval mosquito species were examined as indicators of potential interspecific competition. Data reveal that Oc. japonicus was the most abundant container-inhabiting mosquito species in this survey. It exhibits flexibility in its use of container oviposition habitats, it can persist in a wide range of conditions, and it co-occurs with a wide range of larval mosquito species. Its rapid and successful establishment warrants continued monitoring, because its potential role as a nuisance species or arbovirus vector remains unknown.

Interspecific and intraspecific differences in foraging preferences of container-dwelling mosquitoes.

Feeding preferences of larval container-dwelling mosquitoes are not well understood. Primary production is often absent in container systems and external inputs of animal and plant detritus supply the energy base of container food webs by supporting microorganism prey for mosquitoes. We quantified the feeding preferences of Aedes albopictus (Skuse), a non-native invasive mosquito, and Ochlerotatus triseriatus (Say), a native mosquito, when given a choice of animal and plant detritus. We tested for interpopulational (Illinois versus Florida) differences in feeding preferences, and quantified each species' performance on these two detritus types. When given a choice, both species spent significantly more time feeding at an animal detritus patch. The Illinois populations of both species spent more time feeding at animal detritus patches than did the Florida populations, which spent more time feeding at leaf detritus than did Illinois populations. Both species reached a later instar and had higher survival when reared with animal versus leaf detritus. Ae. albopictus spent more time feeding at animal detritus and had higher survival when reared on either detritus type compared with Oc. triseriatus. Greater preference for and better performance exhibited by Ae. albopictus in high-quality food (animal detritus) may result in preemption of high quality food and may contribute to the superior competitive ability of Ae. albopictus relative to Oc. triseriatus.

Timing of resource input and larval competition between invasive and native container-inhabiting mosquitoes (Diptera: Culicidae).

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.

Establishment of Ochlerotatus japonicus (Diptera: Culicidae) in Ontario, Canada.

Ochlerotatus (Finlaya) japonicus (Theobold) is newly established in Ontario, Canada. It was first discovered in 2001 during the province-wide West Nile virus mosquito surveillance program implemented by the Ontario Ministry of Health and Long Term Care. Although the numbers of adults trapped in CDC light traps were low in 2001 and 2002, they increased during the 2003 and 2004 surveillance seasons. Oc. japonicus larvae also have been collected in large numbers in the Niagara Peninsula in a variety of natural and artificial containers. The number of health units with records for Oc. japonicus has increased over the 4 yr of surveillance, illustrating the ability of this species to rapidly extend its range. As a potential arboviral bridge vector, its establishment in Ontario requires further study and should be considered a public health concern.

Interisland dispersal of the black salt marsh mosquito, Ochlerotatus taeniorhynchus (Diptera: Culicidae) in the Florida Keys.

Mark-release-recapture experiments were conducted in 2001 and 2002 to determine whether Ochlerotatus taeniorhynchus, black salt marsh mosquitoes, were dispersing from uninhabited islands in the Key Deer National Wildlife Refuge to inhabited islands within Monroe County, Florida. An estimated 1,658,000 mosquitoes were marked during 2001, and an estimated 300,000 mosquitoes were marked during 2002. Recapture rates were 0.0061% and 0.0117%, respectively. Oc. taeniorhynchus disperse from uninhabited islands to other uninhabited islands and also to inhabited islands, namely, Big Pine Key and No Name Key.

Ochlerotatus japonicus japonicus in the state of Kentucky.

Ochlerotatus j. japonicus (Theobald) was first collected and identified in 2003 from CDC gravid trap collections in Boone, Campbell, and Wolfe counties, Kentucky. Subsequent collections during 2004 and 2005 indicate that the species has become established in Boone, Campbell, Fayette, Fleming, Grant, Jefferson, and Kenton counties.

[Parity of Ochlerotatus scapularis in laboratory and field conditions]. / Paridade de Ochlerotatus scapularis em condições de laboratório e campo.

OBJECTIVE: To identify the parity status of Ochlerotatus scapularis females in laboratory and field conditions. METHODS: Field collections were carried out fortnightly using a hand-held aspirator in Vale do Ribeira, Southeastern Brazil, from April 2003 to March 2004. In laboratory, 100 Ochlerotatus scapularis F1 females were obtained and followed up individually, reporting the number of blood meals, the length of gonotrophic cycle, survival and number of eggs laid. The parity status and ovarian development were observed through ovarian dissection of 90 field females for each collection and all females reared in laboratory. RESULTS: The parity status diagnoses of the 100 females reared in laboratory and dissected agreed with 55% of the oviposition data, and it was underestimated in 37% and overestimated in 2%. Also in the laboratory, 106 gonotrophic cycles were completed, around 55% of females needed more than one blood meal before laying eggs. In laboratory conditions the species survival was 26 days. A total of 1,180 field females of Ochlerotatus scapularis were dissected: 418 (35.4%) nulliparous, 655 (55.5%) uniparous, 46 (3.9%) biparous and 61 (5.2%) could not be evaluated. Ninety field females were found in Christophers and Mer's phase III-V. CONCLUSIONS: The gonotrophic discordance hypothesis could be confirmed based on field and laboratory observations of Ochlerotarus scapularis females.