Culex quinquefasciatus: status as a threat to island avifauna and options for genetic control
Tim Harvey‐SamuelThomas H. AntJolene T. SuttonChris N. NiebuhrSamoa AsigauPatricia G. ParkerSteven P. SinkinsLuke Alphey
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Abstract The avifauna endemic to islands is particularly susceptible to population declines and extinctions resulting from the introduction of non-native pathogens. Three pathogens of concern are the avian malaria parasites, the avian poxviruses, and West Nile virus—each of which can be transmitted by Culex quinquefasciatus , a highly adaptive and invasive mosquito. Culex quinquefasciatus has dramatically expanded its range in recent centuries and is now established throughout much of the tropics and sub-tropics, including on many islands that are remote from mainland landmasses and where this geographic separation historically protected island species from mosquito-borne diseases. The potential for ecological disruption by Cx. quinquefasciatus has been particularly striking in the Hawaiian Islands, where the introduction and transmission of avian malaria and avian poxvirus led to the extinction of several endemic bird species, with many more at risk. With Cx. quinquefasciatus now present in many insular communities and global trade and tourism increasing links between these areas, both to each other and to mainlands, there is growing concern that patterns of avian decline in Hawai‘i may be played out in other insular ecosystems. The implementation of traditional methods for Cx. quinquefasciatus control, including larval source management, is often impractical at large scale and when breeding sites are numerous and difficult to locate—typical issues associated with invasive species removal. One alternative approach would be the utilisation of genetic control methods, several of which have been successfully developed in other mosquitos such as Aedes aegypti and the malaria vector Anopheles gambiae . However, the development of similar tools for Cx. quinquefasciatus has been comparatively limited. Here we review the threat that Cx. quinquefasciatus poses as a vector of avian pathogens to island avifauna and discuss specific examples of at-risk bird populations on the islands of Hawai‘i, New Zealand and Galápagos. We also review the major options for the deployment of genetic control tools against Cx. quinquefasciatus , and discuss the current state of the field with a focus on radiation-based sterilisation, transgenic methods, and transinfections using the bacterial endosymbiont Wolbachia .Keywords:
Culex quinquefasciatus
Avian Malaria
The southern house mosquito, Culex quinquefasciatus Say is a major mosquito vector of West Nile virus in the southern United States. The regional temperature and precipitation are key factors to the population dynamics of the mosquito Culex quinquefasciatus. The understanding of the relations between climatic conditions and Culex mosquito dynamics has an important implication for the management of WNV outbreaks in the southern United States and elsewhere. We analyzed the monthly averages of minimum and maximum temperatures, precipitation amount, and mosquito samplings in two years 2011-2012. Warm temperature along with at least above precipitation during the study period appears to have facilitated the mosquito abundance. An important finding is the potential influence of early warmer spring with relatively high rainfalls increased the WNV vector population in 2012. In addition, continuous precipitation in the summer period maintains the vector population, which appears to be a causative factor of the WNV outbreak in the region. Awareness of such two climate factors at beginning of the spring and summer may help to predict the WNV disease risk.
Culex quinquefasciatus
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Most reports from the United States suggest Culex quinquefasciatus mosquitoes feed minimally on humans. Given the abundance of C. quinquefasciatus in residential Tucson and parts of metropolitan Phoenix, and the arrival of West Nile virus to this area, discovering the blood meal hosts of the local population is important. Using a sandwich ELISA technique, the local C. quinquefasciatus were found to feed on both humans and birds. This suggests they should be considered potential West Nile virus vectors.
Culex quinquefasciatus
Blood meal
West Nile virus
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Objective:To observe ultrastructures of the eggs,larvae,pupae and adults of Aedes albopictus,Culex quinquefasciatus,Anopheles sinensis and Culex barraudi.Method:The four species mosquitoes were collected in the breeding places,and the ultrastructures were observed under the scanning electron microscope(SEM).Results:Some features could be clearly differentiate among these mosquitoes especially comb scales in larval stages,scutellum in adults,siphon and surface morphology in pupae,and some surface mophologic structures in eggs.Conclusion:New morphological features of these four species are found under SEM,which can be used for taxonomic identification.
Aedes albopictus
Culex quinquefasciatus
Anopheles sinensis
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The employment of avian plasmodia is emphasized for solving problems related to human malaria. Models of research with avian malaria parasites are reported, which can be applied to various studies of chemotherapeutics, pathology, immunology and biology of malaria.
Avian Malaria
Plasmodium (life cycle)
Malarial parasites
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Abstract Background Plasmodium parasites that cause bird malaria occur in all continents except Antarctica and are primarily transmitted by mosquitoes in the genus Culex . Culex quinquefasciatus , the mosquito vector of avian malaria in Hawaiʻi, became established in the islands in the 1820s. While the deadly effects of malaria on endemic bird species have been documented for many decades, vector-parasite interactions in avian malaria systems are relatively understudied. Methods To evaluate the gene expression response of mosquitoes exposed to a Plasmodium infection intensity known to occur naturally in Hawaiʻi, offspring of wild-collected Hawaiian Cx. quinquefasciatus were fed on a domestic canary infected with a fresh isolate of Plasmodium relictum GRW4 from a wild-caught Hawaiian honeycreeper. Control mosquitoes were fed on an uninfected canary. Transcriptomes of five infected and three uninfected individual mosquitoes were sequenced at each of three stages of the parasite life cycle: 24 h post feeding (hpf) during ookinete invasion; 5 days post feeding (dpf) when oocysts are developing; 10 dpf when sporozoites are released and invade the salivary glands. Results Differential gene expression analyses showed that during ookinete invasion (24 hpf), genes related to oxidoreductase activity and galactose catabolism had lower expression levels in infected mosquitoes compared to controls. Oocyst development (5 dpf) was associated with reduced expression of a gene with a predicted innate immune function. At 10 dpf, infected mosquitoes had reduced expression levels of a serine protease inhibitor, and further studies should assess its role as a Plasmodium agonist in C. quinquefasciatus . Overall, the differential gene expression response of Hawaiian Culex exposed to a Plasmodium infection intensity known to occur naturally in Hawaiʻi was low, but more pronounced during ookinete invasion. Conclusions This is the first analysis of the transcriptional responses of vectors to malaria parasites in non-mammalian systems. Interestingly, few similarities were found between the response of Culex infected with a bird Plasmodium and those reported in Anopheles infected with human Plasmodium . The relatively small transcriptional changes observed in mosquito genes related to immune response and nutrient metabolism support conclusions of low fitness costs often documented in experimental challenges of Culex with avian Plasmodium .
Culex quinquefasciatus
Avian Malaria
Plasmodium (life cycle)
Anopheles gambiae
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Population growth and urbanization have increased the potential habitats, and consequently the abundance of Culex quinquefasciatus, the southern house mosquito, a vector of West Nile Virus in urban areas. Water quality is critical in larval habitat distribution and in providing microbial food resources for larvae. A mesocosm experiment was designed to demonstrate which specific components of water chemistry are conducive to larval Culex mosquitoes. Dose-response relationships between larval development and NO3 , NH4 , and PO4 concentrations in stream water were developed through this experiment to describe the isolated effects of each nutrient on pre-adult development. The emergence pattern of Culex mosquitoes was found to be strongly related to certain nutrients, and results showed that breeding sites with higher PO4 or NO3 concentrations had higher larval survival rates. High NO3 concentrations favor the development of male mosquitoes and suppress the development of female mosquitoes, but those adult females that do emerge develop faster in containers with high NO3 levels compared to the reference group. The addition of PO4 in the absence of nitrogen sources to the larval habitat slowed larval development, however, it took fewer days for larvae to reach the pupal stage in containers with combinations of NO3 and PO4 or NH4 and PO4 nutrients. Results from this study may bolster efforts to control WNV in urban landscapes by exploring water quality conditions of Culex larval habitats that produce adult mosquitoes.
Culex quinquefasciatus
Mosquito control
Aedes albopictus
Mesocosm
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The occurrence of larvae of two potential vectors of West Nile virus, Culex nigripalpus and Culex quinquefasciatus, was examined in the Florida Keys. About half of the aquatic habitats examined contained larvae of either one or both of the species. Culex quinquefasciatus was the most frequently encountered species, whereas only 9% of habitats sampled contained Culex nigripalpus. Over half of those samples that contained Culex nigripalpus also contained Culex quinquefasciatus. The two species utilize similar larval habitats in the Florida Keys, Monroe County, Florida, USA.
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West Nile virus
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Background: West Nile virus (WNV) infection, is an arbovirus infection with high morbidity and mortality, the vector responsible for both human and animal transmission is Culex pipens complex.Objective: To determine the species distribution and seasonal abundance of Culex pipens and Culex quinquefasciatus mosquitoes in Abeokuta, Nigeria.Methods: Mosquitoes belonging to the Culex pipens complex were captured in three different locations located within Abeokuta Metropolis between March 2012 and January 2013. Individual species were identified using morphometric methods. Amplification of the Ace2 gene by PCR confirmed morphormetric identification of the mosquitoes.Results: A total of 751 mosquitoes were captured. Culex quinquefaciatus recorded the highest distribution of vectors with 56.6% and Culex pipens 43.4% (P > 0.05). Idi aba community recorded the highest distribution of mosquito vectors with 42.9% (n=322) and Culex quinqueaciatus was more abundantly distributed with 183 mosquitoes. Aro community recorded 32% (n=240) of captured mosquitoes with Culex quinquefaciatus having a higher level of abundance and lastly Kemta with a distribution of 25.1% (n=189).Conclusion: Results from this study show that potential vectors of WNV abound within Abeokuta, putting residents at high risk of West Nile infection. We advocate for introduction of routine testing of WNV in Abeokuta and Nigeria.Keywords: West Nile Virus, Culex pipens complex, PCR, Abeokuta
Culex quinquefasciatus
West Nile virus
Arbovirus Infections
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SummaryCulex tarsalis, Culex stigmatosoma and Culex quinquefasciatus were susceptible to infection with and capable of transmitting to canaries local strains of Plasmodium relictum.Culex tarsalis and Culex stigmatosoma were more easily infected with these strains than was Culex quinquefasciatus. This observation affords an explanation for the difference in natural infection rates observed in other studies.
Culex quinquefasciatus
Avian Malaria
Plasmodium (life cycle)
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