Ochlerotatus Detritus Research Articles

Modeling the effects of species associations and abiotic parameters on the abundance of mosquito species in a Mediterranean wetland

Recent outbreaks of the West Nile virus have been reported in southern Spain, a region with important wetland habitats for migratory birds. Here, we analyzed the role of species association and abiotic parameters on the abundance of seven mosquito species in the Doñana National Park, Spain. We applied the Joint Species Distribution Models (JSDM), using the Hierarchical Modeling of Species Communities approach to simultaneously model the effect of habitat type, normalized difference vegetation index, hydroperiod, distance to rivers, land surface temperature, and the abundance of seven mosquito species. We created three models with varied parameters and evaluated the effects of abiotic parameters and species-to-species associations, which served as proxies for species interactions. Our models estimated the species-specific responses of the mosquito community to abiotic parameters. A positive association was identified within the Culex community with potential biotic interactions. However, Ochlerotatus caspius, Ochlerotatus detritus, and Anopheles atroparvus had no statistically significant association with each other and with the Culex species after accounting for the effect of abiotic parameters. We also found that the potential species associations estimated at particular sites and abiotic parameters influenced the model projection for the average abundance of mosquito species. The JSDM will allow spatial projection of the abundance of each mosquito species, which is an important parameter for epidemiological models. The JSDM inference of species association is important because predation, competition, and facilitation affect the distribution and abundance of different species.

A new microsporidian parasite of the genus Amblyospora (Hazard and Oldacre, 1975) identified from the halophilic mosquito Ochlerotatus detritus (Haliday, 1833) (Diptera: Culicidae) through rDNA ITS sequencing

Ochlerotatus detritus (Haliday, 1833) from Parkgate marshes, Wirral, UK are shown to be parasitised by a new species of Amblyospora (Hazard and Oldacre, 1975) microsporidian. Phylogenetic analysis shows that Internal Transcribed Spacer sequences from this microsporidian are distinct from those of all known microsporidia identified to date, but form a clade with Amblyospora weiseri Lukeš and Vávra, 1990 and A. stictici Andreadis, 1994, microsporidia identified from Ochlerotatus cantans Meigen, 1818 and O. sticticus Meigen, 1838, respectively. Prevalence rates, from pooled samples (N = 5 per pool) were low (2.37%; lower limit 0.78%, upper limit 5.62%), which may be a consequence of these ephemeral brackish water pool habitats periodically drying out. There is increasing interest in the use of microsporidian parasites as novel vector control strategies and understanding the phenology of this microsporidian and its mosquito host may ultimately lead to new methods of control for this nuisance biting species.

Laboratory transmission potential of British mosquitoes for equine arboviruses

BackgroundThere has been no evidence of transmission of mosquito-borne arboviruses of equine or human health concern to date in the UK. However, in recent years there have been a number of outbreaks of viral diseases spread by vectors in Europe. These events, in conjunction with increasing rates of globalisation and climate change, have led to concern over the future risk of mosquito-borne viral disease outbreaks in northern Europe and have highlighted the importance of being prepared for potential disease outbreaks. Here we assess several UK mosquito species for their potential to transmit arboviruses important for both equine and human health, as measured by the presence of viral RNA in saliva at different time points after taking an infective blood meal.ResultsThe following wild-caught British mosquitoes were evaluated for their potential as vectors of zoonotic equine arboviruses: Ochlerotatus detritus for Venezuelan equine encephalitis virus (VEEV) and Ross River virus (RRV), and Culiseta annulata and Culex pipiens for Japanese encephalitis virus (JEV). Production of RNA in saliva was demonstrated at varying efficiencies for all mosquito-virus pairs. Ochlerotatus detritus was more permissive for production of RRV RNA in saliva than VEEV RNA. For RRV, 27.3% of mosquitoes expectorated viral RNA at 7 days post-infection when incubated at 21 °C and 50% at 24 °C. Strikingly, 72% of Cx. pipiens produced JEV RNA in saliva after 21 days at 18 °C. For some mosquito-virus pairs, infection and salivary RNA titres reduced over time, suggesting unstable infection dynamics.ConclusionsThis study adds to the number of Palaearctic mosquito species that demonstrate expectoration of viral RNA, for arboviruses of importance to human and equine health. This work adds to evidence that native mosquito species should be investigated further for their potential to vector zoonotic mosquito-borne arboviral disease of equines in northern Europe. The evidence that Cx. pipiens is potentially an efficient laboratory vector of JEV at temperatures as low as 18 °C warrants further investigation, as this mosquito is abundant in cooler regions of Europe and is considered an important vector for West Nile Virus, which has a comparable transmission ecology.

Potential for Zika virus transmission by mosquitoes in temperate climates.

Mosquito-borne Zika virus (ZIKV) transmission has almost exclusively been detected in the tropics despite the distributions of its primary vectors extending farther into temperate regions. Therefore, it is unknown whether ZIKV's range has reached a temperature-dependent limit, or if it can spread into temperate climates. Using field-collected mosquitoes for biological relevance, we found that two common temperate mosquito species, Aedes albopictus and Ochlerotatus detritus, were competent for ZIKV. We orally exposed mosquitoes to ZIKV and held them at between 17 and 31°C, estimated the time required for mosquitoes to become infectious, and applied these data to a ZIKV spatial risk model. We identified a minimum temperature threshold for the transmission of ZIKV by mosquitoes between 17 and 19°C. Using these data, we generated standardized basic reproduction number R0-based risk maps and we derived estimates for the length of the transmission season for recent and future climate conditions. Our standardized R0-based risk maps show potential risk of ZIKV transmission beyond the current observed range in southern USA, southern China and southern European countries. Transmission risk is simulated to increase over southern and Eastern Europe, northern USA and temperate regions of Asia (northern China, southern Japan) in future climate scenarios.

Pathogenicity and environmental tolerance of commercial and UK native entomopathogenic nematodes (Steinernema and Heterorhabditis spp.) to the larvae of mosquitoes (Aedes aegypti and Ochlerotatus detritus)

Many vector mosquito species have evolved resistance to chemical insecticides and the search for novel biological control strategies warrants further attention. Entomopathogenic nematodes (EPNs) (Heterorhabditis and Steinernema spp.) have been developed as biological control agents for use against agricultural pests but whether they could be used to control aquatic mosquito larvae warrants further research. We exposed Aedes aegypti and Ochlerotatus detritus larvae to commercially available (Steinernema feltiae, S. carpocapsae, S. kraussei and Heterorhabditis bacteriophora) and wild isolated (S. affine and S. glaseri) EPNs and monitored survival over 7 days. We also exposed EPNs to water with a range of salinities and pHs found in the marshland habitats of British mosquitoes. Ae. aegypti and O. detritus were killed by commercial EPNs, but wild strains were unable to kill Ae. aegypti yet did kill O. detritus. All EPNs were capable of tolerating a wide range of pHs but showed variable tolerance to different salinities. EPNs could be used as an alternative to chemical insecticides but target species and habitat may influence choice of EPN strain in control operations.

Carbamate resistance in a UK population of the halophilic mosquito Ochlerotatus detritus implicates selection by agricultural usage of insecticide

The salt marsh mosquito Ochlerotatus detritus Haliday, 1833 (Diptera: Culicidae) is locally abundant in some areas of the UK, can be a pernicious summer nuisance biter and is one of eleven British mosquitoes considered as a potential bridge vector of West Nile Virus. WHO bioassays of insecticide susceptibility were performed on O. detritus from Parkgate Marshes, Little Neston, Wirral, UK using three insecticides, the pyrethroid permethrin, the carbamate bendiocarb and the organophosphate fenitrothion. O. detritus were fully susceptible to permethrin and fenitrothion but exhibited strong resistance to bendiocarb (66% of females alive following 1–hr exposure; LT50 of 116 minutes). Sequencing of the known resistance-causing mutations in the acetylcholinesterase target site of carbamate/organophosphates, and of pyrethroids, the voltage-gated sodium channel, revealed no known target-site mutations indicating the carbamate resistance is not target-site mediated. Pre-exposure to the synergist piperonyl butoxide recovered full bendiocarb susceptibility further implicating metabolic resistance. We show that UK mosquitoes have the potential to develop resistance to insecticides and suggest that the carbamate resistance detected could be a result of exposure to agricultural insecticides.

Mosquito species involved in the circulation of West Nile and Usutu viruses in Italy.

Usutu (USUV) and West Nile (WNV) are mosquito-borne Flavivirus emerged in Italy in 1996 and 1998, respectively, and reappeared 10 years later. The aim of this work is to review the Italian mosquito species found positive for WNV and USUV between 2008 and 2014. Moreover, the role of mosquitoes in promoting the overwintering of these viruses is discussed, as a result of the mosquito collections performed in Molise region between September 2010 and April 2011. Overall 99,000 mosquitoes were collected: 337 and 457 mosquito pools tested positive by real time reverse transcriptase polymerase chain reaction (real time RT-PCR) for WNV and USUV, respectively. West Nile virus was detected in pools of Culex pipiens s.l. (329), Ochlerotatus caspius (4), Culex modestus (2), and Culex spp. (2). Positive USUV pools were from Cx. pipiens s.l. (435), Aedes albopictus (12), Oc. caspius (5), Culex spp. (2), Anopheles maculipennis s.l. (1), Culiseta annulata (1), and Ochlerotatus detritus (1). In Molise region, 1,694 mosquitoes were collected, and USUV was identi ed in Cx. pipiens s.l., Cs. annulata, and Oc. detritus pools. This paper shows that Cx. pipiens s.l. is the mosquito species most involved in the WNV and USUV circulation in Italy, although other species would also support the spread of both the viruses during Winter.

Geospatial techniques for environmental modeling of mosquito breeding habitats at Suez Canal Zone, Egypt

Egypt is currently witnessing a number of mega projects, along the axis of Suez Canal, which consequently have a great effect on environment and its biological components including mosquito vectors of diseases. This study is an attempt to explore the use and efficiency of integrated remote sensing-GIS techniques and field surveys for detection of mosquito breeding habitats at Suez Canal Zone. Remote sensing and field surveys provided the necessary verified ground truth information to the present study. A corrected Landsat8 image, acquired in Jan. 2015, was utilized to produce NDVI, NDMI and LST to identify environmental variables associated with mosquitoes breeding habitats. Concurrently, a GIS model was developed to predict probable mosquito habitats and areas under environmental risk of diseases transmission. Results revealed that Culex pipiens and Ochlerotatus detritus are the most abundant species in Suez Canal Zone recording total number of 362 larvae (51.86%) and 244 larvae (34.96%), respectively. The model predicted that Ismailia is the most subjected Suez Canal Governorate to mosquito borne diseases. It recorded the maximum levels of high risk, risk and vulnerable areas to mosquito proliferation; 6.06km2 (64.26%), 954.65km2 (54.58%) and 152.87km2 (80.09%), respectively. The developed prediction model achieved an accuracy of 80.95% and increased to 100% at sites where predicted larval habitats were ascertained by in-situ checks.

Potential vectors of equine arboviruses in the UK

There is growing concern about the increasing risk of disease outbreaks caused by arthropod-borne viruses (arboviruses) in both human beings and animals. There are several mosquito-borne viral diseases that cause...

Evaluation of the vector competence of a native UK mosquito Ochlerotatus detritus (Aedes detritus) for dengue, chikungunya and West Nile viruses.

BackgroundTo date there has been no evidence of mosquito-borne virus transmission of public health concern in the UK, despite the occurrence of more than 30 species of mosquito, including putative vectors of arboviruses. The saltmarsh mosquito Ochlerotatus detritus [syn. Aedes (Ochlerotatus) detritus] is locally common in parts of the UK where it can be a voracious feeder on people.MethodsHere, we assess the competence of O. detritus for three major arboviruses: dengue virus (DENV), chikungunya virus (CHIKV) and West Nile virus (WNV) using adult mosquitoes reared from wild, field-obtained immatures.ResultsWe demonstrate laboratory competence for WNV at 21 °C, with viral RNA detected in the mosquito’s saliva 17 days after oral inoculation. By contrast, there was no evidence of laboratory competence of O. detritus for either DENV or CHIKV.ConclusionsTo our knowledge, this is the first study to demonstrate competence of a UK mosquito for WNV and confirms that O. detritus may present a potential risk for arbovirus transmission in the UK and that further investigation of its vector role in the wild is required.

Landscape Effects on the Presence, Abundance and Diversity of Mosquitoes in Mediterranean Wetlands.

Environment determines the distribution of mosquito-borne diseases in that it influences the vector-host-pathogen transmission cycle, including vector distribution, abundance and diversity. In this study, we analyse the relationship between environmental variables estimated by remote sensing and the spatial distribution (presence, abundance and diversity) of seven mosquito species vectors of West Nile and other pathogens (Usutu, avian malaria and dirofilariasis) in the Doñana Natural Park, Spain. Traps were distributed over an area of 54,984 ha divided into six ecological units: marshland, sand dunes, scrubland, ricefields, crops and fishponds. We collected mosquitoes once a month from up to 112 locations using BG-Sentinel traps baited with BG-lure and CO2 during March-November 2010. Hydroperiod, NDVI and Inundation surface were estimated at several resolution scales (100, 250, 500, 1000 and 2000 metres) from corrected and normalized Landsat Images. We sampled 972,346 female mosquitoes, the most abundant species being Culex theileri, Ochlerotatus caspius, Culex modestus, Culex perexiguus, Culex pipiens, Anopheles atroparvus and Ochlerotatus detritus. Our results suggest that: (1) hydroperiod, inundation surface and NDVI are strongly related to the spatial distribution of mosquitoes; (2) the spatial scales used to measure these variables affected quantification of these relationships, the larger scale being more informative; (3) these relationships are species-specific; (4) hydroperiod is negatively related to mosquito presence and richness; (5) Culex abundance is positively related to hydroperiod; (6) NDVI is positively related to mosquito diversity, presence and abundance, except in the case of the two salt marsh species (Oc. caspius and Oc. detritus); and (7) inundation surfaces positively condition the abundance and richness of most species except the salt marsh mosquitoes. Remote sensing data provided reliable information for monitoring mosquito populations. Landscape significantly affected mosquito distribution and abundance, and as a result may alter disease risk. These results suggest that while environmental conditions affect the distribution and abundance of mosquitoes, other factors such as human modification of landscapes may give rise to significant changes in mosquito populations and consequently disease risk.

Recent entomological enquiry on mosquito fauna in Circeo National Park.

The present study was carried out in Circeo National Park (Lazio region, Central Italy), in order to collect data about mosquito (Diptera, Culicidae) fauna in a protected area for biodiversity. From 2003 to 2004 seasonal surveys allowed to collect and to identify 380 larvae and 713 adult mosquitoes in 6 sites. A total of 15 mosquito species belonging to 6 genera were recorded; the most abundant species were Culex pipens Linnaeus, 1758 known as the main West Nile virus vector, Ochlerotatus detritus (Haliday, 1933) and Culiseta annulata (Dhrank, 1776). Present data show a noteworthy number of other mosquito species, even if less abundant, reflecting the considerable environmental richness. Respect to the past collections of Anophelinae mosquitoes carried out in the same area once affected by malaria, the present research represents the first monitoring of the whole Culicidae Family in Circeo National Park, up to now. This paper reports the collected data as a first base for a future checklist in this protected area.

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.

A multiplex PCR to differentiate the two sibling species of mosquitoes Ochlerotatus detritus and Oc. coluzzii and evidence for further genetic heterogeneity within the Detritus complex

Internal transcribed spacer regions of ribosomal DNA were sequenced, and species-specific primers were designed to simplify the identification of two morphologically similar species of the Detritus complex, Ochlerotatus detritus and Ochlerotatuscoluzzii. Each newly designed primer was able to amplify a species-specific fragment with a different size. Samples from France and Germany were successfully tested. This new tool prompts for bio-ecological studies to refine basic knowledge on the bionomics of this species complex, towards a better control and prevention of ensuing nuisances. Moreover, ITS2 sequencing revealed the existence of (1) two distinct haplotypes of Oc. detritus that are sympatric and widely distributed along the French Atlantic and Mediterranean littorals and (2) a specific haplotype in mosquitoes sampled from Tunisia, raising the question of the taxonomic status of this North-African population.

Climatic effects on mosquito abundance in Mediterranean wetlands.

BackgroundThe impact of climate change on vector-borne diseases is highly controversial. One of the principal points of debate is whether or not climate influences mosquito abundance, a key factor in disease transmission.MethodsTo test this hypothesis, we analysed ten years of data (2003–2012) from biweekly surveys to assess inter-annual and seasonal relationships between the abundance of seven mosquito species known to be pathogen vectors (West Nile virus, Usutu virus, dirofilariasis and Plasmodium sp.) and several climatic variables in two wetlands in SW Spain.ResultsWithin-season abundance patterns were related to climatic variables (i.e. temperature, rainfall, tide heights, relative humidity and photoperiod) that varied according to the mosquito species in question. Rainfall during winter months was positively related to Culex pipiens and Ochlerotatus detritus annual abundances. Annual maximum temperatures were non-linearly related to annual Cx. pipiens abundance, while annual mean temperatures were positively related to annual Ochlerotatus caspius abundance. Finally, we modelled shifts in mosquito abundances using the A2 and B2 temperature and rainfall climate change scenarios for the period 2011–2100. While Oc. caspius, an important anthropophilic species, may increase in abundance, no changes are expected for Cx. pipiens or the salt-marsh mosquito Oc. detritus.ConclusionsOur results highlight that the effects of climate are species-specific, place-specific and non-linear and that linear approaches will therefore overestimate the effect of climate change on mosquito abundances at high temperatures. Climate warming does not necessarily lead to an increase in mosquito abundance in natural Mediterranean wetlands and will affect, above all, species such as Oc. caspius whose numbers are not closely linked to rainfall and are influenced, rather, by local tidal patterns and temperatures. The final impact of changes in vector abundance on disease frequency will depend on the direct and indirect effects of climate and other parameters related to pathogen amplification and spillover on humans and other vertebrates.

The impact of some environmental factors on the abundance of mosquitoes larvae in certain localities of Sharkia Governorate in Egypt

Mosquitoes play a major role in diseases transmission and distributions, such as filariasis and malaria. The understanding of environmental factors that affect their larval abundance is a key factor for their control. Thus this study aims at investigating mosquitoes' larval abundance in a region known to be endemic for malaria mosquitoes' related diseases in Sharkia Governorate. Measuring environmental factors were: pH, total dissolved solids “TDS”, turbidity, water and air temperatures, relative humidity, wind speed, water hyacinths, sun light, water flow, and width and depth of drains in relation with these environmental factors on larval abundance. Six mosquitoes species were recorded and identified in different locations from study sites of 9 drains: Abu Kbeer, Dyarb Negm and Al-Zakazik. Culex pipiens, Culex perexiguus, Culex antennatus, Culex pusillus, Culex sinaiticus and Ochlerotatus detritus were found to be dominant in these localities. Culex pipiens was the most dominant species (79.79%) in all localities. Results were shown and discussed in detail.

Population Ecology of Mosquitoes and the Status of Bancroftian Filariasis in El Dakahlia Governorate , the Nile Delta , Egypt

Mosquitoes were surveyed (Oct. 2010 & Apr. - Oct. 2011) in some localities representing 13 centers of El-Dakahlia Governorate. Six mosquito species were collected: Culex pipiens, Cx. antennatus, Cx. perexiguus, Ochlerotatus detritus, Anopheles pharoensis and An. tenebrosus. Culex pipiens was predominating (ca 79% larvae, 51% adults). Culex antennatus and Cx. perexiguus were also common. Of the Four types of the breeding habitats, the drainage canals were the most productive (53.4% larvae). For the three common species, the compiled larval density increases as water temp. increased and decreases as pH increased while adult indoor density increases as indoor and outdoor temp. and indoor RH increased and decreases as outdoor RH increased. Cx. pipiens significantly associated with Cx. antennatus (CAB=0.88 & I=0.48) while Cx. antennatus has a moderate association with Cx. perexiguus (CAB=0.47 & I=0.36). Out of 908 examined blood samples from ten centers, 7.49% were infected with Wuchereria bancrofti. The highest infection rates in some centers were associated with high indoor densities of Cx. pipiens females, the main filariasis vector. The situation necessitates a wide vector control program to minimize lymphatic filariasis transmission in this Governorate.

Host-Feeding Patterns ofCulex pipiensand Other Potential Mosquito Vectors (Diptera: Culicidae) of West Nile Virus (Flaviviridae) Collected in Portugal

The host blood-feeding patterns of mosquito vectors affects the likelihood of human exposure to zoonotic pathogens, including West Nile Virus (family Flaviviridae, genus Flavivirus, WNV). In Portugal, data are unavailable regarding the blood-feeding habits of common mosquito species, including Culex pipiens L., considered the primary vector of WNV to humans. The sources of bloodmeals in 203 blood-fed mosquitoes of nine species collected from June 2007 to November 2010 in 34 Portuguese counties were analyzed by sequencing cytochrome-b partial fragments. Cx. pipiens was the most common species collected and successfully analyzed (n = 135/78). In addition, blood-fed females of the following species were analyzed: Ochlerotatus caspius Pallas (n = 20), Culex theileri Theobald (n = 16), Anopheles maculipennis s.l. Meigen (n = 10), Culiseta longiareolata Macquart (n = 7), Aedes aegypti L. (n = 6), Culex perexiguus Theobald (n = 3), Culiseta annulata Schrank (n = 3), and Ochlerotatus detritus Haliday (n = 3). The Cx. pipiens mosquitoes fed predominantly on birds (n = 55/78, 70.5%), with a high diversity of avian species used as hosts, although human blood was identified in 18 specimens (18/78, 23.1%). No significant differences were found between the host-feeding patterns of blood-fed Cx. pipiens collected in residential and nonresidential habitats. The occurrence of human derived blood meals and the presence of a mix avian-human bloodmeal accordingly suggest this species as a potential vector of WNV. Therefore, in Portugal, Cx. pipiens may play a role both in the avian-to-avian enzootic WNV cycle and in the avian-to-mammal transmission. In this context, the identity of Cx. pipiens (considering the forms molestus and pipiens) and the potential consequence on feeding behavior and WNV transmission are discussed.

Mosquitoes (Diptera: Culicidae) in El Gharbia Governorate, Egypt: their spatial distribution, abundance and factors affecting their breeding related to the situation of lymphatic filariasis

Mosquitoes were surveyed (March - May, and November 2007) in all centers of the El Gharbia Governorate. Seven mosquito species (6 culicine and 1 anopheline) were collected. These are Culex pipiens, Cx. perexiguus, Cx. antennatus, Cx. theileri, Ochlerotatus detritus, Culiseta longiareolata and Anopheles tenebrosus. Cx. pipiens, the main filariasis vector was the most common or predominating species (ca. 45%, 15 adult/room and 86%, 63 larva/SU, P<0.01). Cx. antennatus (ca. 38%, 13 adult/room) was also common species (P<0.01). For the three common species, Cx, pipiens, Cx. perexiguus and Cx. antennatus the relation of their larval and adult indoor densities with the environmental factors (water temperature and pH; indoorand outdoor- temperature and RH) were examined. No infection with Wuchereria bancrofti were found in 1493 blood sample examined. Only one Elephantiasis case was reported from El Santa center (1/ 196 examined sample).

Checklist and Pictorial Key to Fourth-Instar Larvae of Mosquitoes (Diptera: Culicidae) of Saudi Arabia

The Kingdom of Saudi Arabia includes fauna from three zoogeographic regions: the Afrotropical, Oriental, and Palaearctic regions. To study the mosquito (Diptera: Culicidae) fauna of these regions in Saudi Arabia, larval collections were made at 15 sites during 2005-2006. Thirty-three species representing nine genera were found. Six species, Anopheles culicifacies Giles s.l., Anopheles subpictus Grassi s.l., Culex arbieeni Salem, Culex simpsoni Theobald, Culex univittatus Theobald, and Ochlerotatus detritus Haliday are reported for the first time for Saudi Arabia. An annotated checklist and an illustrated key to the fourth-instar larvae of the 33 species are presented, along with some remarks about problematic species. Eleven species of genus Anopheles Meigen, five species of tribe Aedini, 13 species of genus Culex L., two species of genus Culiseta Felt, one species of genus Lutzia Theobald, and one species of genus Uranotaenia Lynch Arribátlzaga were recorded during the study.