In spring 2017, mosquito larvae were collected from 25 sites across eastern Oklahoma as part of a Zika virus vector surveillance effort. Aedes japonicus japonicus larvae were collected from horse troughs at 2 sites in Ottawa County, OK. Identification was made using 1 larva stored in 70% ethanol and 3 adult females reared from the larvae. Another invasive mosquito species, Culex coronator, was detected at 2 different sites, adding 2 additional counties to the 9 where the species had been previously reported. The presence of these invasive species in Oklahoma may have an impact on future regional arbovirus concerns.
Aedes japonicus japonicus (Theobald), the Asian bush mosquito, is a species associated with rock pools, tree holes, and artificial containers throughout the world (Kampen and Werner 2014). Previously found in Taiwan, Japan, Korea, and parts of Russia and China, this species has successfully invaded and become established in many regions of the world since 1993 (Kampen and Werner 2014). Invasion of the USA was first detected in New York, New Jersey, and Connecticut in 1998. By 2012, Ae. japonicus had been collected in most states east of the Mississippi River (except Louisiana), and movement was detected into the Great Plains states (Iowa, Missouri) (Kaufman and Fonseca 2014). The invasion of southern US states happened later than the northern US states, with Arkansas (2010) and Mississippi (2011) being the most recent states to report occurrence. To date, no occurrence of Ae. japonicus has been reported in Oklahoma or Texas.
In the USA, Ae. japonicus is not considered a major vector of pathogens that affect humans or animals. Field-collected mosquitoes have been detected with West Nile virus (Sardelis and Turell 2001) and La Crosse encephalitis virus (US) (Sardelis et al. 2002b), while the species has demonstrated competency in the laboratory for Japanese encephalitis virus (Asia) (Takashima and Rosen, 1989), St. Louis encephalitis virus (Sardelis et al. 2003), eastern equine encephalomyelitis virus (Sardelis et al. 2002a), Rift Valley fever virus (Turell et al. 2013), and chikungunya and dengue viruses (Schaffner et al. 2011). Although the role of this invasive mosquito in vectorborne disease transmission still appears limited, its reported presence in Missouri (Gallitano et al. 2005) and Arkansas (Gaspar et al. 2012) suggested that occurrence in Oklahoma was likely and needed to be investigated.
The Ae. japonicus larvae collected in eastern Oklahoma during this study occurred as part of a Zika vector surveillance program funded by the Centers for Disease Control and Prevention through the Oklahoma State Department of Health. For this part of the study, a wide variety of artificial habitats (waste tires, buckets, troughs, various sizes of plastic containers, and a water-filled boat) and some natural pools were sampled in eastern Oklahoma between I-40 in the south and the Kansas border in the north. Known for its proclivity to use rural or wooded sites more than urban sites, a focus was made on artificial containers that could be easily sampled along roads in rural areas of eastern Oklahoma (Fig. 1). The location of each sampling site was recorded by geographical positioning system (Table 1). In the laboratory, collected larvae were placed in mosquito breeders (Bioquip, Rancho Dominguez, CA) that were held in an environmental chamber (25°C, 14:10 h day:night) until all the mosquitoes eclosed. Upon eclosion, female mosquitoes were identified by 3 persons using the criteria of Darsie and Ward (2005).
On June 6, 2017, mosquito larvae, including Ae. japonicus, were collected from a horse trough in a rural area near Quapaw in northeastern Ottawa County, OK (Fig 1). The site was 5.5 mi (8.8 km) northeast of Peoria, OK, on State Line Road between Missouri and Oklahoma. All but 1 larvae were reared to adults. For identification purposes, 1 larva was placed in 70% ethanol and identified using the larval key provided by Darsie and Ward (2005). While most resulting female mosquitoes were Aedes epactius (Dyar and Knab) (n = 3), 1 of the emerged females was identified as an Ae. japonicus specimen. At the time of collection, 1 adult female mosquito was captured on the horse trough water surface and later identified as Ae. japonicus.
On June 7, 2017, mosquito larvae, including Ae. japonicus, were collected from a horse trough outside of Miami in Ottawa County, OK, 15 mi (24 km) southwest of the first site (Fig. 1). While the majority of the larvae were Ae. epactius, 1 adult female Ae. japonicus was reared and identified. All other surveillance sites in eastern Oklahoma where larvae were collected from a variety of containers yielded a variety of different mosquito species, including Culex coronator Dyar and Knab, but no Ae. japonicus specimens (Table 1). Voucher specimens of the larvae as well as 2 of the Ae. japonicus adults were placed into the K.C. Emerson Entomology Museum housed in the Department of Entomology and Plant Pathology in the Noble Research Center at Oklahoma State University.
This is the first record of Ae. japonicus in the state of Oklahoma. Previous sampling of urban areas using multiple trap types across Oklahoma in summer 2016 detected Aedes aegypti (L.), but no Ae. japonicus individuals were collected (Bradt 2017). The confirmation of Ae. japonicus only in the corner of the northeasternmost county of Oklahoma indicates that this species likely has recently entered the state from Missouri, where the species was first recorded in the St. Louis area (Gallitano et al. 2005). While more investigation is needed to confirm whether the species has become established in northeastern Oklahoma, it is highly likely that this species will continue to spread and become established throughout much of Oklahoma, as it has in other southern states.
In the south-central USA, it appears that Ae. japonicus females deposit their eggs in the same habitats that harbor Ae. epactius Dyar and Knab habitats. In the current Oklahoma-based study, Ae. epactius was identified as the only species cohabitating with A. japonicus during early June. Aedes japonicus larvae were collected together with Ae. epactius in the early summer months during a 2011 survey in northeastern Arkansas (Gaspar et al. 2012). As the season progressed and temperatures increased, Ae. epactius became the dominant species. In the current study, Aedes japonicus specimens were found in rural areas with adjacent heavy tree cover, which is consistent with findings in Arkansas, as well as the rest of the country (Bartlett-Healy et al. 2012, Gaspar et al. 2012, Kampen and Werner 2014, Kaufman and Fonseca 2014). Future work in this region of Oklahoma should include surveys of rock pools and tree holes in rural areas, as these are other sites where Ae. japonicus have been collected in the USA (Andreadis et al. 2001, Gaspar et al. 2012). While unclear how the species will interact with local mosquito fauna and adapt to the unique environmental challenges in Oklahoma, it will be necessary to continue monitoring the expansion of this species, particularly as we continue to discover the role this invasive species may play in the transmission of diseases that impact humans or animals.
The collection of Cx. coronator larvae at 2 sites in eastern Oklahoma indicates that the species has continued to spread in the state since the first report of its presence in 2003 in McAlester, OK (Noden et al. 2015). The collection of Cx. coronator in Haskell (Stigler) and Cherokee (Tahlequah) counties brings the reported distribution of the species in Oklahoma up to 11, including Pittsburg, Sequoyah, Payne, Comanche, Oklahoma, Garfield, Jackson, McCurtain, and Carter counties (Paras et al. 2014, Noden et al. 2015, Bradt 2017). Since 2003, this invasive mosquito has been recorded across southern (Altus, Lawton, Ardmore, and Idabel), central (Midwest City), and northern Oklahoma (Enid) (Bradt 2017) and in Stillwater, OK (Paras et al. 2014). An invasive species that originated in Central America (Dyar and Knab 1906), Cx. coronator has been recorded in all southern states, starting in New Mexico, Arizona, and Texas (Darsie and Ward 2005), and spreading to Oklahoma (Noden et al. 2015), Louisiana (Debboun et al. 2005), Mississippi (Goddard et al. 2006), Alabama (McNelly et al. 2007), Georgia (Moulis et al. 2008), and Florida (Smith et al. 2006). Like Ae. japonicus, the importance of Cx. coronator in the transmission of pathogens in the United States remains to be determined, although it has been identified as a potential vector for West Nile virus in Florida (Alto et al. 2014) as well as other arboviruses (Gray et al. 2008).
We thank Hassan Melouk and Wyatt Hoback for constructive comments on an earlier version of this manuscript. This project was funded through support from an Epidemiology and Laboratory Capacity for Infectious Diseases Cooperative Agreement (5-U50-CK000406), funded by the Centers for Disease Control and Prevention (CDC). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the CDC or the Oklahoma Department of Health and Human Services. Partial funding for this project was also provided by National Institute of Food and Agriculture/US Department of Agriculture Hatch Grant funds through the Oklahoma Agricultural Experiment Station (OKL-02909).