ABSTRACT
Invasive organisms may cause ecologic, economic, and public health harm. Aedes japonicus is an invasive mosquito species of known ecologic and public health importance that has widely spread throughout the eastern USA since initially being recognized in Connecticut in 1998. Here, we report the known distributions of Ae. japonicus within the Great Smoky Mountains National Park (GSMNP) since its initial recognition in the park in 2004. From 2006 to 2022, we sampled eggs, larvae, and adult life stages through targeted, haphazard, and convenience collections. Through these efforts, we surveyed 23 (54.7%) of the 42 watersheds within the GSMNP. Aedes japonicus was present in 19 (82.6%) of the sampled watersheds, and the species was confirmed, in some instances, at the same location over multiple years, suggesting it remains entrenched. This species was observed in 45.2% of the GSMNP watersheds at elevations ranging from 347 to 1,478 m. Naturally occurring containers (i.e., riverine rock pools) were common collection sites in this study. The results of our findings are presented in the context of the species distribution within the park, the public health relevance given the GSMNP’s public visitation rate (>12 million annually), potential species interactions, and the persistence of this species over the multiyear study.
Aedes japonicus (Theobald) was initially recognized in New York and New Jersey, USA, in 1998 (Peyton et al. 1999). During the past 25 years, this species has spread to 7 Canadian provinces and 38 states, including North Carolina and Tennessee (Peach et al. 2019, Sames et al. 2022, Cawthon et al. 2023, Monath 2023). There is molecular evidence of multiple introductions since the initial recognition (Kaufman and Fonseca 2014, Monath 2023). This invasive mosquito is known to have complex interactions with other container-inhabiting species and is commonly found in riverine rock pools in the southern Appalachian Region (Byrd et al. 2019). From a public health perspective, it is considered a secondary vector of La Crosse virus (LACV), and there are multiple reports detecting West Nile virus in field collected samples (Kaufman and Fonseca 2014, Westby et al. 2015).
Located along the border of North Carolina and Tennessee, the Great Smoky Mountains National Park (GSMNP) contains more than 522,000 acres and receives >12 million visitors annually, more than any other US national park. The GSMNP also contains over 2,100 mi (3,360 km) of riverine ecosystems and is located within a known focus of endemic LACV transmission (National Park Service [NPS] 2015, Davis et al. 2024). Indeed, there are reports of LACV exposure likely occurring in GSMNP visitors, with some historical reports dating back to 1965 (Kelsey and Smith 1978). Therefore, the invasion and entrenchment of Ae. japonicus within the GSMNP has direct public health relevance.
Here, we document the known distributions of Ae. japonicus within the GSMNP since its incidental recognition in a study of trichomycete insect symbionts in 2004 (White et al. 2006). We sampled Ae. japonicus eggs, larvae, and adult life stages within the GSMNP through a series of targeted surveys and haphazard or convenience collections from 2006 to 2022 (Table 1). Mosquitoes were identified using a stereomicroscope (total magnification 90X, Olympus SZ61; Olympus, Waltham, MA) and a dichotomous key (Darsie and Ward 2005). Samples were primarily taken as larvae from riverine rock pools within the GSMNP during the months of May–October. Additional collections from ovitraps, CO2-baited Centers for Disease Control and Prevention light traps, and incidental (landing mouth aspiration) encounters with host-seeking adults also yielded Ae. japonicus. Other mosquito species found in rock pools with Ae. japonicus included Ae. atropalpus (Coquillett), Culex territans (Walker), and Anopheles punctipennis (Say); ovitraps that contained Ae. japonicus frequently yielded both Ae. albopictus (Skuse) and Ae. triseriatus (Say) (Table 1). These observations are consistent with other studies in the region (Byrd et al. 2019, Tamini et al. 2021).
Riverine rock pools are well established as suitable habitat for Ae. japonicus in the southern Appalachian Region, and some authors have postulated movement through riverine corridors (Gray et al. 2005, Byrd et al. 2019). Thus, we organized our collections based on watershed systems with the GSMNP. In total, 23 of the 43 total watersheds in the GSMNP were surveyed, and Ae. japonicus was present in 19 watersheds, representing 82.6% of watersheds surveyed and 45.2% of the total watersheds in the park (Fig. 1). Aedes japonicus was also observed in the same watersheds, including the same collection location, over multiple years, demonstrating that this species is likely well established in the park.
Survey for Aedes japonicus in the Great Smoky Mountains National Park (NPS 2015); Ae. japonicus collected from the dark grey watersheds (“*” denotes watershed with Ae. japonicus): 1) Chilhowee Lake, Little Tennessee River; 2) Lower Abrams Creek*; 3) Lake Cheoah, Little Tennessee River; 4) Hesse Creek, Little River; 5) Upper Abrams Creek*; 6) Eagle Creek; 7) Lower Fontana Lake, Little Tennessee River; 8) Rudd Branch, Little River*; 9) West Prong, Little River*; 10) Hazel Creek*; 11) Walden’s Creek; 12) Goshen Prong, Little River*; 13) Forney Creek; 14) Nolan Creek*; 15) Fontana Lake, Tuckasegee River; 16) Upper West Prong Little Pigeon River*; 17) Le Conte Creek*; 18) Baskin’s Creek; 19) Roaring Fork; 20) Deep Creek*; 21) Bird Creek; 22) Dudley Creek*; 23) Upper Little Pigeon River*; 24) Porter’s Creek; 25) Upper Oconaluftee River*; 26) Kirkland Creek, Tuckasegee River; 27) Lower Oconaluftee River*; 28) Webb Creek; 29) East Fork Little Pigeon River; 30) Middle Prong Little Pigeon River; 31) Bradley Fork; 32) Upper Raven Fork; 33) Lower Raven Fork; 34) Cosby Creek*; 35) Cripple Creek, Pigeon River; 36) Big Creek*; 37) Cold Springs Creek, Pigeon River; 38) Straight Fork Raven Fork; 39) Palmer Creek*; 40) Cataloochee Creek*; 41) Walter’s Lake, Pigeon River; and 42) Lower Jonathan Creek.*
Survey for Aedes japonicus in the Great Smoky Mountains National Park (NPS 2015); Ae. japonicus collected from the dark grey watersheds (“*” denotes watershed with Ae. japonicus): 1) Chilhowee Lake, Little Tennessee River; 2) Lower Abrams Creek*; 3) Lake Cheoah, Little Tennessee River; 4) Hesse Creek, Little River; 5) Upper Abrams Creek*; 6) Eagle Creek; 7) Lower Fontana Lake, Little Tennessee River; 8) Rudd Branch, Little River*; 9) West Prong, Little River*; 10) Hazel Creek*; 11) Walden’s Creek; 12) Goshen Prong, Little River*; 13) Forney Creek; 14) Nolan Creek*; 15) Fontana Lake, Tuckasegee River; 16) Upper West Prong Little Pigeon River*; 17) Le Conte Creek*; 18) Baskin’s Creek; 19) Roaring Fork; 20) Deep Creek*; 21) Bird Creek; 22) Dudley Creek*; 23) Upper Little Pigeon River*; 24) Porter’s Creek; 25) Upper Oconaluftee River*; 26) Kirkland Creek, Tuckasegee River; 27) Lower Oconaluftee River*; 28) Webb Creek; 29) East Fork Little Pigeon River; 30) Middle Prong Little Pigeon River; 31) Bradley Fork; 32) Upper Raven Fork; 33) Lower Raven Fork; 34) Cosby Creek*; 35) Cripple Creek, Pigeon River; 36) Big Creek*; 37) Cold Springs Creek, Pigeon River; 38) Straight Fork Raven Fork; 39) Palmer Creek*; 40) Cataloochee Creek*; 41) Walter’s Lake, Pigeon River; and 42) Lower Jonathan Creek.*
Notably, Ae. japonicus was collected across a wide range of elevations from 347 to 1,478 m (Table 1), which supports prior observations that elevation may not grossly constrain the distribution of the mosquito in the southern Appalachians (Bevins 2007). Aedes atropalpus, an autogenous native rock pool species, was occasionally observed with Ae. japonicus; however, most of the rock pools that contained mosquito larvae did not contain the native species. Prior studies in the region suggest that riverine rock pools that are less exposed (i.e., shaded) and maintain cooler temperatures are more likely to contain Ae. japonicus (Byrd et al. 2019). Most rivers and creeks within the GSMNP are narrow and have well-established tree canopies at the riverbanks; some primary creeks are completely covered by canopies. Taken together, most of the riverine rock pools within the GSMNP are likely highly suitable habitat for the invasive species. Unfortunately, little is known about the historical distribution of Ae. atropalpus within the GSMNP, and the impacts of competition or other interactions between these species remain unresolved; however, cooler water temperatures may limit Ae. atropalpus population growth in the southern Appalachian Region (Armistead et al. 2008, Byrd et al. 2019, Day et al. 2021).
The extensive distribution of Ae. japonicus within the park has potential public health implications. Although the relative importance of Ae. japonicus in endemic arbovirus transmission remains unclear, it is a competent vector of LACV and has been found naturally infected with the virus in eastern Tennessee (Sardelis et al. 2002, Westby et al. 2015). From 2000 to 2020, North Carolina reported an average of 17 neuroinvasive LACV infections annually, with most (>90%) occurring in western North Carolina counties, including counties containing or bordering the GSMNP (Davis et al. 2024). The GSMNP is the most visited US national park, with more than 12 million annual visitors; many visitors will camp, hike, or otherwise recreate within the park boundaries and therefore risk direct exposure to Ae. japonicus. Given the high volume of annual visitors, public health messaging to park visitors emphasizing personal protection measures (i.e., effective repellents registered with the US Environmental Protection Agency, protective clothing to minimize exposed skin, and the use of screens or nets when camping) to prevent exposure is appropriate during the summer and early fall (i.e., May–September) when LACV disease is most prevalent in the region.
The NPS is tasked, as are all federal agencies (Executive Order 13112), to prevent, detect, respond to, and monitor invasive species through practical programmatic and research efforts. Here, we document the presence of Ae. japonicus, an invasive mosquito, in >40% of the GSMNP watersheds and repeated observations at the same collection location over multiple years. Taken together, these observations suggest the entrenchment of this invasive species within the GSMNP. However, this scientific note is limited, and our observations likely do not completely define the distribution of Ae. japonicus within the GSMNP. Similarly, the observations reported here were conducted over more than 15 years and do not address the seasonality or relative abundance of Ae. japonicus in the GSMNP. Additional longitudinal surveys within the park are warranted.
Mosquito sampling within the Great Smoky Mountains National Park was authorized through approved scientific research and collecting permits (study GRSM-02323); the 2006 and 2007 surveys were supported, in part, through Discover Life in America (project 2006-18). We are grateful for the field assistance of many Western Carolina University (ENVH-431 Medical Entomology Laboratory) and University of Florida student volunteers (2006–23).
REFERENCES CITED
Author notes
The findings and conclusions in this article are those of the authors and do not necessarily represent the official position of the National Park Service or the Centers for Disease Control and Prevention
Mosquito and Vector-Borne Infectious Disease Laboratory, Western Carolina University, 3971 Little Savannah Road, Cullowhee, NC 28723
Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, 3156 Rampart Rd., Ft. Collins, CO 80521
Great Smoky Mountains National Park, National Park Service, 1316 Cherokee Orchard Rd., Gatlinburg, TN 37738