Floodwater Mosquitoes Research Articles

Current and Future Probability of Occurrence of the Floodwater Mosquito Aedes vexans (Meigen, 1830) in the Netherlands

ABSTRACTAedes vexans (Meigen, 1830) is a floodwater mosquito species that may cause significant nuisance and can serve as a vector for multiple arboviruses. Its distribution is expected to shift in the future as a result of changes in climate and land use. Understanding these shifts is important for estimating future disease risk. This study aims to identify habitat suitability and probability of occurrence of A. vexans. Using the Netherlands as a case study, we utilised an occurrence dataset generated by the Netherlands Centre for Monitoring of Vectors. We employed an auto machine learning approach to model generation, using a variety of modelling methodologies, determining the optimal ratio of presence: Absence datapoints in the training data and ultimately creating a 10‐model ensemble. We selected predictor variables relating to weather, land use, soil properties, flood risk and salinity. The probability of A. vexans presence was predicted on a 1 km grid for both the current Dutch situation and for four scenarios for 2050. Our analysis identified temperature, soil type and land cover as the primary determinants influencing the probability of A. vexans occurrence. Future projections reveal an increase in the likelihood of A. vexans occurrence in the study area, particularly along major river corridors and in regions with increasing amounts of artificial and natural areas. Additionally, the mosquito season is predicted to become longer under all future scenarios. Insights provided in our study can also be applied to other similar areas, such as other north‐western European countries or other urban deltas. This study shows for the first time detailed future occurrence predictions and also future seasonal predictions for this mosquito species. Seasonal predictions allow researchers to study how disease risk changes throughout the year, something which is particularly valuable given the predicted lengthening of the mosquito (and thus disease transmission) season.

Citizen complaints in local media as source of mosquito data: the case of Aedes albifasciatus in an intermediate city of temperate Argentina.

Floodwater mosquitoes provoke nuisance due to their mass emergence. Citizen complaints about outstanding events of mosquitoes in urban areas are usually reflected in local media and could be potentially used as data. Our objective was to build a temperature dependent function to characterize the immature development time of the floodwater mosquito Ae. albifasciatus in Tandil (Argentina), and validate it using citizen complaints in local media and field collected mosquitoes. The development time obtained ranges from 5-47 days at 30-7°C, respectively. During 2000-2021, nine mosquito abundance peaks were identified through local journalistic records. For these events, the estimated hatching date was successfully associated with a previous precipitation, with a maximum difference of two days. The precipitation identified as the trigger for egg hatching ranged from 15 to 121 mm. Then, to associate mosquito news with the target species, female mosquitoes were captured by a battery-powered aspirator in green areas of the city during September 2019-June 2021. Six mosquito abundance peaks were detected in which Ae. albifasciatus accounted for 97.3% of the captures. Among them, journalistic records were able to detect the largest two; i.e. in our study above 15 mosquitoes in a five minute collection. Citizen complaints related to nuisance or vector species could be valuable retrospective data for researchers of different fields.

Istraživanje kapaciteta staništa za ovipoziciju jaja poplavnih komaraca na poplavnom prostoru Dunava i Drave, Hrvatska

Floodwater mosquitoes lay their eggs on dry ground where water will eventuallyflood the area. By flooding the area and submerging the eggs of floodwater mosquitoes, the development of larvae begins. For a gravid female mosquito, the mostimportant thing is choosing the place where to lay eggs. As part of this research,which was conducted in April and May 2022, soil and leaf samples were taken on anarea of 50 x 50 cm from different altitudes in the area of Dunavac near Ilok (Danube)and Halaševo near Osijek (Drava) in order to determine at which altitude, the largestnumber of eggs are laid. Collected soil was submerged in the laboratory for the purpose of further mosquito development. Part of the larvae was preserved in alcohol,and part of larvae was left to develop into adults, after which species determinationwas carried out. A large difference was found in the potential of breeding sites in thefloodplain of the Drava and Danube, and the number of collected eggs ranged from0 to 66 per sample. The number of individuals sampled in the Danube area was 53,and in the Drava area 133. The individuals sampled in the researched areas weredetermined as Aedes vexans and Aedes sticticus. A large difference in oviposition wasfound in the floodplain of the Danube, while in the floodplain of the Drava, this levelis significantly higher.

Increased abundance of floodwater mosquito species over three seasons in Forshaga municipality, western Sweden

Floodwater mosquitoes are a main cause of mosquito nuisance in several European countries, including Sweden. Since 2002, a large-scale mosquito control programme around the river Dalälven in eastern Sweden targets floodwater mosquito species such as Aedes sticticus. The current study was initiated due to citizen complaints about nuisance mosquitoes around Deje village in Forshaga municipality, a region situated at the river Klarälven in western Sweden. Over three years, 2010-2012, mosquito collections with CDC-light traps and morphological species identification were performed to determine the nuisance causing mosquito species and to describe the seasonality, abundance and species composition of mosquitoes in the area. Over the three years of collections at eight trap sites, mosquito abundance increased with a mean of 282 mosquitoes collected per trap-night in 2010, 702 mosquitoes per trap-night in 2011, and 1,367 mosquitoes per trap-night in 2012. The increase in abundance was mainly due to an increase of floodwater mosquitoes, with Ae. sticticus as the main species. Single traps collected over 5,000 floodwater mosquitoes at several occasions in 2011 and 2012. A correlation between river discharge exceeding 300 m3/s and an increase in floodwater mosquito abundance three weeks later when average air temperatures were around 15 °C could be seen. Interestingly, river discharge was the highest in 2010, however mosquito abundance was higher in both 2011 and 2012. Potentially, the increasing number of diapausing eggs available after each season has contributed to the amplification of the Ae. sticticus population in the region.

Behavior of Aedes albifasciatus (Diptera: Culicidae) larvae from eggs with different dormancy times and its relationship with parasitism by Strelkovimermis spiculatus (Nematoda: Mermithidae).

Aedine mosquitoes go through unfavorable periods as dormant eggs. However, extended dormancy times lead to a depletion of egg reserves, which might be partially compensated by changes in larval-feeding behavior. Changes in larval behavior may also be induced by parasitism by mermithids probably as a strategy to reduce the impact of the parasite on the host. The most abundant floodwater mosquito in southern South America is Aedes albifasciatus (Diptera: Culicidae), a species naturally parasitized by Strelkovimermis spiculatus (Nematoda: Mermithidae). This study aimed to evaluate the behavior of fourth-instar larvae of Ae. albifasciatus from eggs with 2, 4, and 6months of dormancy, parasitized or not by S. spiculatus. To achieve this, eight categories of behavior were defined, and then, each individual was observed for 5min, and its behaviors and their duration were recorded. The behaviors with the highest percentage of observation time were still (50.1%) and wriggle swimming (33.6%), while those with the lowest percentage of observation time were those involving active foraging (less than 8%). A great variability in the behaviors was observed among individuals within the same treatment. The type and duration of each behavior did not vary in relation to egg dormancy time or parasitism, but parasitism affected the level of larval activity. Parasitized larvae performed, on average, fewer behaviors than non-parasitized larvae. This result supports the hypothesis that S. spiculatus parasitism affects the behavior of Ae. albifasciatus larvae by reducing their level of activity.

The transmission ecology of Tahyna orthobunyavirus in Austria as revealed by longitudinal mosquito sampling and blood meal analysis in floodplain habitats

BackgroundTahyna orthobunyavirus (TAHV) is a mosquito-borne virus that may cause mild flu-like symptoms or neurological symptoms in humans. It is historically associated with floodplain habitats in Central Europe, and the mammalophilic floodwater mosquito, Aedes vexans, is thought to be the principal vector. There are few contemporary reports of TAHV transmission ecology within mosquitoes or their vertebrate hosts, and virus infections are rarely reported (and probably seldom diagnosed). The objectives of this study were to survey the mosquito population for TAHV in three floodwater habitats and describe host usage by the predominant floodwater mosquito species to potentially define TAHV transmission at these foci.MethodsWe performed longitudinal mosquito sampling along three major rivers in eastern Austria to characterize the mosquito community in floodplain habitats, and tested for the presence of TAHV in pools of mosquitoes. We characterized TAHV rescued from mosquito pool homogenate by sequencing. We surveyed mosquito host selection by analyzing mosquito blood meals.ResultsWe identified TAHV in two pools of Ae. vexans captured along the Leitha River. This mosquito, and other floodwater mosquitoes, used large mammals (red deer, roe deer, wild boar) as their hosts. The sequence of the rescued virus was remarkably similar to other TAHV isolates from the region, dating back to the first isolate of TAHV in 1958.ConclusionsIn general, we confirmed that TAHV is most likely being transmitted by Ae. vexans, although the precise contribution of vertebrate-amplifying hosts to the ecological maintenance of the virus is unclear. The pattern of host selection matches the estimated exposure of the same large mammal species in the region to TAHV based on a recent serosurvey, but hares were also hosts at the site where TAHV was detected. We also confirm humans as hosts of two floodwater mosquito species, providing a potential mechanism for spillover of TAHV or other mosquito-borne viruses.Graphical

Heterodissemination: precision insecticide delivery to mosquito larval habitats by cohabiting vertebrates

Conventional larvicide delivery strategies originally developed for permanent and floodwater mosquitoes have proved suboptimal in the small, scattered, and cryptic larval habitats preferred by container-inhabiting Aedes mosquitoes. New methods such as autodissemination, wherein adult mosquitoes spread insecticides to their own larval habitats, have been under study. Another novel delivery method termed heterodissemination, i.e. larvicide delivery by other species sharing the same habitats, has also been proposed. We conducted a proof-of-concept study with four independent experiments using American bullfrogs (Lithobates catesbeianus) and green frogs Lithobates clamitans as carriers of pyriproxyfen, an insect growth regulator, under semi-field conditions in three different locations, two in New Jersey, and one in Utah. Frogs with attached slow-release pyriproxyfen tablets were introduced into outdoor enclosures with water containers. Water samples from the containers were periodically tested using larval Aedes albopictus and Culex pipiens mosquitoes to assess mortality and percent eclosure inhibition. Overall pupal mortality [95% credible intervals] estimated by Bayesian analysis for the treatment group was 73.4% [71.3–75.2] compared to 4.1% [2.9–5.5] for the control group. Mortality within treatment groups in four different experiments ranged from 41 to 100%, whereas control mortalities ranged from 0.5% to 11%. We conclude that heterodissemination is a promising and effective approach deserving of further study.

Different Hatching Rates of Floodwater Mosquitoes Aedes sticticus, Aedes rossicus and Aedes cinereus from Different Flooded Environments.

Simple SummaryIn the lower Dalälven region, floodwater mosquitoes cause recurring problems during floods. Since 2002, flooded areas have been treated with Bacillus thuringiensis israelensis (Bti) to control the number of hatching floodwater mosquitoes. The area is composed of both open meadows that are grazed or mowed, as well as unmanaged open meadows and forest areas that are regularly flooded. This study compared the number of mosquito larvae that hatched from soil samples collected from these environmental categories to assess whether management of flooded areas affected mosquito abundance. The results show that fewer mosquitoes hatched from mowed meadows than from the other categories. It was further clear that Aedes cinereus were more abundant in open areas with tussocks while Aedes sticticus were dominating in forests and in open unkept areas, shrubs, and bushes. This difference is important for nuisance management since Aedes cinereus generally fly only short distances and mainly stay in the area where they hatched, while Aedes sticticus is capable to fly long distances and can cause nuisance problems in larger areas.In the lower Dalälven region, floodwater mosquitoes cause recurring problems. The main nuisance species is Aedes (Ochlerotatus) sticticus, but large numbers of Aedes (Aedes) rossicus and Aedes (Aedes) cinereus also hatch during flooding events. To increase understanding of which environments in the area give rise to mosquito nuisance, soil samples were taken from 20 locations from four environmental categories: grazed meadows, mowed meadows, unkept open grassland areas and forest areas. In each location 20 soil samples were taken, 10 from random locations and 10 from moisture retaining structures, such as tussocks, shrubs, piles of leaves, logs, and roots. The soil samples were soaked with tap water in the lab, and mosquito larvae were collected and allowed to develop to adult mosquitoes for species identification. Fewer larvae hatched from mowed areas and more larvae hatched from moisture retaining structure samples than random samples. The results showed that Aedes cinereus mostly hatch from grazed and unkept areas and hatched as much from random samples as from structures, whereas Aedes sticticus and Aedes rossicus hatched from open unkept and forest areas and hatch significantly more from structure samples. When the moisture retaining structures in open unkept areas where Aedes sticticus hatched were identified it was clear that they hatched predominantly from willow shrubs that offered shade. The results suggest that Ae. sticticus and Ae. cinereus favor different flooded environments for oviposition.

EARTH FILL INCREASES EFFICACY AND LONGEVITY OF λ-CYHALOTHRIN RESIDUAL INSECTCIDE TREATMENT OF HESCO® BLAST WALL GEOTEXTILE

The prevention of vector-borne disease to protect the health and readiness of United States forces in the field continues to be a high priority for the US Department of Defense. Previous studies have demonstrated that the risk of human contact with disease-vector mosquitoes and other biting flies can be reduced by applying an insecticide to perimeters of military materials such as camouflage netting or HESCO blast protection wall geotextile already in place around troops in the field. In this study we investigated whether residual pesticide efficacy will persist in the presence of earth fill that is required for operational use of HESCOs, using a warm temperate field site in north Florida. Results from laboratory bioassays measuring mosquito mortality and field collections of natural mosquito populations indicated superior efficacy and greater longevity of pesticide treated geotextile exposed to soil fill. These findings not only support immediate implementation of this technique in US military field scenarios, but also provide evidence that HESCO technology currently used in natural disaster flood control could be leveraged to protect civilian personnel from emerging floodwater mosquitoes.

Daniel A. Strickman 1953–2020

The field of Medical Entomology has lost a valued entomologist, contributor, colleague, and friend. I have personally lost a close friend with whom I have spent years with discussing pressing challenges in mosquito biology and control. I first met Dan when we both were graduate students with Professor William R. Horsfall at the University of Illinois at Urbana-Champaign. Dan earned his MS in 1976 and Ph.D. in 1978. We both worked on floodwater mosquitoes. Dan and I used to jokingly argue about who processed more dirt from Allerton Park on the Sangamon River floodplain looking for eggs and oviposition sites. We both learned operational mosquito control as entomologists for the Macon Mosquito Abatement District in Decatur, IL. Dan was a quiet man with a unique sense of humor coupled with an outstanding logic for problem solving. He was naturally inquisitive and definitely not dogmatic. He was open and loved to discuss well thought out mosquito and vector control challenges, especially when based on data, observation, or documented information.Dr. Strickman was interested in insects and arthropods at an early age and began his pursuit towards his future professional career as a biologist/entomologist at Dartmouth College and received his Bachelor of Science degree at the University of California-Riverside in 1974.During his career, Dr. Strickman worked in a broad scope of professional responsibilities including medical entomology, operational pest and vector control, research, and management. His career spanned areas from a field researcher to administrative positions in the US military as Chief of Department of Entomology at Walter Reed Army Institute of Research, and the US Department of Agriculture where he held the position of National Program Leader for Veterinary Medical and Urban Entomology and the Acting Director of Overseas Biological Control Laboratories. Although his dominant research focused on mosquitoes, he also worked and contributed knowledge from his studies of tabanids, chiggers, and rodents. His expertise on the parasites and insect vectors causing rickettsia, malaria, and dengue were also key areas and research challenges that intrigued him. His contributions made a significant impact to our knowledge of these vectors regarding both their biology and control. He authored 115 peer-reviewed articles, 16 book chapters, and four books. During his career, an example of his valued expertise is illustrated in the breadth of positions he held, beginning with the US State Department (Peace Corps), the US military (22 years in the Air Force and Army), mosquito abatement (Santa Clara County, CA), the US Department of Agriculture Agricultural Research Service (National Program Leader for Veterinary, Medical, and Urban Entomology and Director of Overseas Laboratories), and finally the Bill & Melinda Gates Foundation (Senior Program Officer, Malaria and Neglected Tropical Diseases). Even in retirement Dan drove to his entomological roots by volunteering his expertise to the Burke Museum of Natural History at the University of Washington, working to curate and examine the museum's collection of fossil insects.During his career, he spent 10 years in countries outside of the USA, including in Latin America, Southwest Asia, East Asia, and Europe. His awards reflect his quality and contributions, including the US military's Legion of Merit and Bronze Star, the US EPA Bronze Medal, the Presidential GreenGov award, the American Mosquito Control Association's John Belkin Award, and the Society for Vector Ecology's Lifetime Achievement Award. Dan was instrumental in supporting the Society of Vector Ecology's annual student competition as our Gates Foundation representative. Dan served on the Editorial Board of the Journal of the American Mosquito Control Association for 13 years.His most recent book is Mosquitoes of the World, to appear in print in 2020 (D. Strickman, R.C. Wilkerson, and Y.-M. Linton, Johns Hopkins University Press). This final work by Dan will be published posthumously. A tribute for a true medical entomologist, a vector control specialist and biologist. He will be missed by many. We have lost a dedicated scholar, colleague, and friend of the American Mosquito Control Association.

Transcriptome studies of the floodwater mosquito, Aedes vexans (Diptera: Culicidae) with potential as secondary vectors using Illumina HiSeq 4,000 sequencing

AbstractAedes vexans is the inland floodwater mosquito widely distributed in every continent excepting Antarctica and South America. They are opportunistic feeders preferring blood meal of larger animals including cattle, horses, deer, and humans. Further, the mosquito species is a compatible vector of several diseases, including West Nile virus and dog heartworm. In this study, we performed transcriptome characterization of Ae. vexans using Illumina HiSeq 4,000 sequencing and assembly of sequenced reads using Trinity. A total of 55,813,852 raw read and 54,630,771 clean reads (97.88% of raw reads) were obtained after Illumina paired‐end sequencing and pre‐processing steps. After Trinity de novo assembly, TransDecoder and TGICL clustering, a total of 37,111 unigenes were obtained. Out of the total unigenes count, 28,733, 17,893, 14,626, and 17,055 showed homologous matches against the PANM, UniGene, SwissProt, and KOG databases. A total of 9,483 unigenes were assigned to Gene Ontology (GO) terms, and 3,741 unigenes were mapped to 483 KEGG pathways. The zinc finger (C2H2‐type), reverse transcriptase, integrase (catalytic core), protein kinase, and RNA recognition motif domain among others showed as the top InterProScan domains. The obtained datasets serves as a basis for future studies towards understanding ecology, metabolism, and parasitism potential of Ae. vexans.

Field-captured Aedes vexans (Meigen, 1830) is a competent vector for Rift Valley fever phlebovirus in Europe

BackgroundAedes vexans (Meigen) is considered a nuisance species in central Europe and the Mediterranean region. It is an anthropophilic and mammalophilic floodwater mosquito involved in the transmission of several arboviruses. Rift Valley fever (RVF) is a relevant mosquito-borne zoonosis, affecting mainly humans and ruminants, that causes severe impact in public health and economic loses. Due to globalization and climate change, the European continent is threatened by its introduction. The main purpose of the present study was to evaluate the vector competence of a European field-collected Ae. vexans population.MethodsAedes vexans field-collected larvae were reared in the laboratory under field-simulated conditions. To assess the vector competence for Rift Valley fever phlebovirus (RVFV) transmission, adult F0 females were exposed to infectious blood meals containing the 56/74 RVFV strain. Additionally, intrathoracic inoculations with the same virus strain were performed to evaluate the relevance of the salivary gland barriers. Natural circulation of alphavirus, flavivirus and phlebovirus was also tested.ResultsTo our knowledge, an autochthonous Ae. vexans population was experimentally confirmed as a competent vector for RVFV for the first time. This virus was capable of infecting and disseminating within the studied Ae. vexans mosquitoes. Moreover, infectious virus was isolated from the saliva of disseminated specimens, showing their capacity to transmit the virus. Additionally, a natural infection with a circulating Mosquito flavivirus was detected. The co-infection with the Mosquito flavivirus seemed to modulate RVFV infection susceptibility in field-collected Ae. vexans, but further studies are needed to confirm its potential interference in RVFV transmission.ConclusionsOur results show that field-collected European Ae. vexans would be able to transmit RVFV in case of introduction into the continent. This should be taken into consideration in the design of surveillance and control programmes.

Controlling floodwater mosquitoes by river regulation

AbstractFloodwater mosquitoes cause serious problems especially the spread of mosquito‐borne diseases. The main challenge is to implement acceptable general mitigation methods. In recent years, encouraging steps have been taken in favour of developing more sustainable measures such as modern biological methods. The novelty of the present study is in suggesting an alternative green method that can eliminate the use of any secondary biological or chemical agents. The method is based on establishing an alternative river regulation scheme that limits flooding of high‐risk lowland areas. A combined hydrodynamic modelling and optimization method gave effective river regulation schemes. The main idea is to maintain the total power production for a modified inflow hydrograph. The approach was applied to a 30‐km reach of the Österdalälven River located in central Sweden. It was found that with the specific constraints of the site a reduction of about 8% of lowland flood areas is possible if the inflow hydrograph is moderately modified by 20%. Higher reductions are possible by further modification of the hydrograph. The proposed method has a general character controlled by the specific site requirements of a critical flow or a water surface elevation. Based on the foregoing information, the method can be applied to similar sites.

Zoonotic Rift Valley fever virus prevalence and risk factors in the Lake Zone of Tanzania

Zoonotic Rift Valley fever virus prevalence and risk factors in the Lake Zone of Tanzania

Seasonal and Environmental Variables Related to the Abundance of Immature Mosquitoes in Rain Pools of a Peri-Urban Park of Buenos Aires (Argentina).

The aim of the present study was to investigate the variables associated with the composition of mosquito species in rain pools of 'Bosque de Ezeiza', a large peri-urban forested park of Buenos Aires city, Argentina. A total of 12 rain pools were sampled biweekly over a 1-yr period in search of mosquito immature stages. Mosquito immature stages were present in all the occasions in which water bodies were recorded. A total of 14 species of five genera were identified, with the highest abundances observed in autumn and spring. The total abundance varied among dates according to previous temperature, precipitation, and flooding conditions. Only one species, Psorophora cyanescens (Coquillett) (Diptera: Culicidae), was associated with extreme conditions (high temperature and prolonged period of drought). Besides drought periods, two main variables were related to species composition: temperature, which accounted for seasonal changes in species composition, and flooding history, which accounted for the predominance of floodwater mosquito species on recently flooded dates and for that of stagnant water species on dates with a longer permanence of water. Regarding the pools, the most important variables accounting for species composition were the insolation level and the variability in the flooded area, with floodwater mosquitoes associated with pools with high variability in the flooded area. Interestingly, Culex (Mel.) pilosus (Dyar and Knab) (Diptera: Culicidae) showed temporal and spatial dynamics more similar to floodwater species than to stagnant water species in the rain pools studied.

Lack of Resistance in Aedes vexans Field Populations After 36 Years of Bacillus thuringiensis subsp. Israelensis Applications in the Upper Rhine Valley, Germany.

Bacillus thuringiensis subsp. israelensis (Bti) has been widely and solely used against floodwater mosquitoes, mostly Aedes vexans, for 36 years in the Upper Rhine Valley by the German Mosquito Control Association. During this period, almost 5,000 tons of Bti formulations were applied to an area of approximately 400,000 ha. To investigate a possible resistance development after such a long-term and widespread application of Bti, the susceptibility of Ae. vexans larvae to Bti in 3 untreated (Lake Constance) and 6 treated areas on both sides of the Rhine within the Upper Rhine Valley was assessed by bioassays following World Health Organization guidelines. Comparing log-probit analyses, it was shown that neither the median lethal concentration (LC50 values) nor slopes of the probit lines of bioassays of the larvae deriving from treated and untreated areas showed significant differences. These results have been confirmed by resistance ratios, which varied from 0.80 to 1.12 in all tests. The results provided the evidence that no restistance in the target species Ae. vexans has developed in the areas of the Upper Rhine Valley, despite the large-scale use of Bti for 36 years.

Pest occurrence of Aedes rossicus close to the Arctic Circle in northern Sweden.

Major nuisance species are found among the floodwater mosquitoes and snow-pool mosquitoes, with the former being the main reason for mosquito control in most areas. Nuisance species vary with the area, and previous reports from northern areas conclude that the nuisance is most often caused by snow-pool mosquitoes. We investigated the mosquito fauna and abundances of host-seeking females using CDC traps baited with carbon dioxide, in Övertorneå city near the Arctic Circle in northern Sweden, after earlier complaints about massive mosquito nuisance. The abundance of host-seeking female mosquitoes was high in 2014, with a maximum of ∼15,400 individuals per CDC trap night, of which 89% was the floodwater mosquito Aedes rossicus. Surprisingly, the main nuisance species was a floodwater mosquito, occurring at the northernmost location it has ever been recorded in Sweden. Our report is probably the first documentation of such large numbers of Aedes rossicus in any locality and probably the first documentation of a severe floodwater mosquito nuisance near the Arctic Circle. Given the historical data on river discharge in the area, the nuisance is recurrent. We conclude that in northern localities, as well as in more southern localities, production of floodwater mosquitoes is a natural component of the floodplain fauna of rivers with a fluctuating water flow regime. Also, the floodwater mosquitoes Aedes sticticus and Aedes vexans were found north of their formerly known distribution in Sweden.

Effects of Irrigation and Rainfall on the Population Dynamics of Rift Valley Fever and Other Arbovirus Mosquito Vectors in the Epidemic-Prone Tana River County, Kenya.

Rift Valley fever (RVF) is a mosquito-borne viral zoonosis that is found in most regions of sub-Saharan Africa, and it affects humans, livestock, and some wild ungulates. Outbreaks are precipitated by an abundance of mosquito vectors associated with heavy persistent rainfall with flooding. We determined the impact of flood-irrigation farming and the effect of environmental parameters on the ecology and densities of primary and secondary vectors of the RVF virus (RVFV) in an RVF-epidemic hotspot in the Tana River Basin, Kenya. Mosquito sampling was conducted in farms and villages (settlements) in an irrigated and a neighboring nonirrigated site (Murukani). Overall, a significantly higher number of mosquitoes were collected in farms in the irrigation scheme compared with villages in the same area (P < 0.001), or farms (P < 0.001), and villages (P = 0.03) in Murukani. In particular, key primary vectors of RVFV, Aedes mcintoshi Marks and Aedes ochraceous Theobald, were more prevalent in the farms compared with villages in the irrigation scheme (P = 0.001) both during the dry and the wet seasons. Similarly, there was a greater abundance of secondary vectors, particularly Culex univittatus Theobald and Culex pipiens (L.) in the irrigation scheme than in the Murukani area. Rainfall and humidity were positively correlated with mosquito densities, particularly the primary vectors. Adult floodwater mosquitoes and Mansonia spp. were collected indoors; immatures of Ae. mcintoshi and secondary vectors were collected in the irrigation drainage canals, whereas those of Ae. ochraceous and Aedes sudanensis Theobald were missing from these water bodies. In conclusion, irrigation in RVF endemic areas provides conducive resting and breeding conditions for vectors of RVFV and other endemic arboviruses.

First Record and Larval Habitat Description of Culex (Melanoconion) pilosus from Buenos Aires Province, Argentina.

Larvae of Culex (Melanoconion) pilosus were collected during February-April 2014 in temporary pools in "Bosques de Ezeiza," a large forested park, near Buenos Aires city, Argentina. This is the first record in Buenos Aires Province, extending the distribution of this species 380 km to the south. Regarding habitat use, Cx. (Mel.) pilosus is a generalist, although a slight association of larval abundances with pools of lower pH and higher vegetation cover was observed. The comparison of larval instars of Cx. (Mel.) pilosus with those of other genera suggests a life-history strategy similar to that of floodwater mosquitoes.

Specific detection of the floodwater mosquitoes Aedes sticticus and Aedes vexans DNA in predatory diving beetles.

Floodwater mosquitoes (Diptera: Culicidae) are associated with periodically flooded wet meadows, marshes, and swamps in floodplains of major rivers worldwide, and their larvae are abundant in the shallow parts of flooded areas. The nuisance caused by the blood-seeking adult female mosquitoes motivates mosquito control. Larviciding with Bacillus thuringiensis israelensis is considered the most environmentally safe method. However, some concern has been raised whether aquatic predatory insects could be indirectly affected by this reduction in a potential vital prey. Top predators in the temporary wetlands in the River Dalälven floodplains are diving beetles (Coleoptera: Dytiscidae), and Aedes sticticus and Ae. vexans are the target species for mosquito control. For detailed studies on this aquatic predator-prey system, we developed a polymerase chain reaction (PCR) assay for detection of mosquito DNA in the guts of medium-sized diving beetles. Primers were designed for amplifying short mitochondrial DNA fragments of the cytochrome C oxidase subunit I (COI) gene in Ae. sticticus and Ae. vexans, respectively. Primer specificity was confirmed and half-life detectability of Ae. sticticus DNA in diving beetle guts was derived from a feeding and digestion experiment. The Ae. sticticus DNA within diving beetle guts was detected up to 12 h postfeeding, and half-life detectability was estimated to 5.6 h. In addition, field caught diving beetles were screened for Ae. sticticus and Ae. vexans DNA and in 14% of the diving beetles one or both mosquito species were detected, showing that these mosquito species are utilized as food by the diving beetles.