The aim of this study was to consolidate mosquito information for 13 counties west of San Antonio, Bexar County, Texas, and to create a species checklist for future regional studies. The resulting checklist established a baseline for local mosquito-borne disease surveillance and can serve as a resource for public health officials. The 13 counties in this region were Bandera, Edwards, Kendall, Kerr, Kimble, Kinney, Maverick, Medina, Real, Sutton, Uvalde, Val Verde, and Zavala counties. To develop the checklist, county-level mosquito species data were extracted from 38 peer-reviewed publications and government documents, university reference collections, private collections, and the Texas Department of State Health Services' historical collection data. These data were combined with author field collections to create a comprehensive species list. Overall, 339 county-level records were documented through field studies with a total of 36 species representing 8 genera confirmed as being present in this region. An additional 14 species listed in historical surveillance records were not collected during this study.
This study was conducted in Bandera, Edwards, Kendall, Kerr, Kimble, Kinney, Maverick, Medina, Real, Sutton, Uvalde, Val Verde, and Zavala counties. This 13-county region covers 46,405 km2 (17,917 mi2), is west of San Antonio, and extends to the Texas-Mexico border (Fig. 1). Interstate Highway 10 and US Routes 57, 83, 90, and 277 are the major international and interstate highways going through this region. These counties lie in a transition zone between 2 Level III ecological zones: the Edwards Plateau to the north and the South Texas Plains to the south (Griffith et al. 2004). Within this semiarid landscape, mosquito densities are generally low with occasional spikes caused by rain and where human activities provide or support mosquito habitats. Mosquito surveillance and control in this region are minimal.
Historically, reported cases of mosquito-borne diseases in this 13-county region have been infrequent. In 1923, 3 cases of dengue fever were reported in Bandera County (Duggan 1925), and Bohls and Irons (1942) reported possible eastern (EEE) and western equine encephalomyelitis (WEE) virus infections in Maverick County. Later Olson and Grimes (1974) collected and tested mosquitoes in Dimmit and Maverick counties in response to the 1971 Venezuelan equine encephalitis (VEE) outbreak, which resulted in 4 WEE, 1 St. Louis encephalitis virus (SLE), and 6 VEE isolates. The outbreak affected equines in 6 counties in this region: Edwards, Kinney, Maverick, Medina, Val Verde, and Zavala counties; and Maverick County also had human cases (Zehmer et al. 1974).
As for malaria, Barber et al. (1929) did not find evidence of malaria transmission in Val Verde County during field studies, and Faust (1941) showed, as a 10-year summary (1929–1938), malaria morbidity to be less than 25 per 100,000 population in Kendall, Maverick, Medina, Uvalde, and Zavala counties.
West Nile virus (WNV) was first documented in Texas in 2002 (Lillibridge et al. 2004). Texas Department of State Health Services (Texas DSHS) records show that from 2002 to 2020, 47 equine and 10 human cases were reported from the 13-county region, but no virus-positive mosquito pools or avian samples were reported. No WNV cases of any type were reported from Real or Sutton counties (Texas DSHS 2020).
The perceived lack of mosquito problems and mosquito-borne disease is partly confounded by the lack of surveillance. No full-time vector surveillance or mosquito control personnel are employed in this region, and only the cities of Eagle Pass (Maverick County), Hondo (Medina County), Uvalde (Uvalde County), Del Rio and Laughlin Air Force Base (AFB) (Val Verde County), and Sonora (Sutton County) have had at least 1 person who conducted mosquito control on a part-time basis or as an extra duty.
Since 2002, only the city of Sonora participated in the Texas DSHS arbovirus surveillance program over multiple years by submitting mosquito samples for species identification and virus testing. Laughlin AFB routinely submitted mosquito collections to the United States Air Force (USAF) for species identification. The authors did not find any records of mosquito surveillance or control activities being conducted in Bandera, Edwards, Kendall, Kerr, Kinney, Kimble, Real, or Zavala counties from 2002 to 2020.
With limited mosquito surveillance in the region and the presence of primary disease vectors, Aedes aegypti (L.), Ae. albopictus (Skuse), Culex quinquefasciatus Say, and Cx. tarsalis Coquillett, the aim of this study was to update and summarize mosquito information for these 13 counties. The aim of this study was to combine historical county-level mosquito collection records from valid sources with contemporary author collections to update state and local health departments as a resource for mosquito-borne disease surveillance.
MATERIALS AND METHODS
This study was conducted from January 2017 through December 2020. For the years 2018–2020, all counties in this study were designated as being in drought conditions by the Secretary of the US Department of Agriculture (USDA 2020). Drought conditions delayed the study and increased the difficulty in finding less common tree hole and floodwater species. Similarly, species associated with permanent bodies of water such as swamps or wetlands were also difficult to collect in large numbers. Despite the drought, sufficient mosquito populations were present following infrequent rains and in habitats created and maintained through human activities to support the collection efforts and results of this study.
To create the checklist, county-level mosquito species data were extracted from peer-reviewed publications and government documents, specimens in university and private collections, and the Texas Department of State Health Services. When found, outdated taxonomic names were updated as appropriate. These data were combined with the author collections to create a comprehensive species list.
From peer-reviewed or government documents, county-level mosquito species data were extracted from 38 sources. The Texas A&M University Insect Collection (TAMUIC), College Station, TX, the University of Texas Biodiversity Collection (UTBC), Austin, TX, and the mosquito collection at Sam Houston State University, Huntsville, TX, were visited, and county-level data were extracted from curated specimens. Data from county submissions to Texas DSHS for identification and testing were acquired for the years 2002–2020.
Author collections were made to fill data gaps and verify the presence of species previously reported. Larvae were collected using dippers, basters, bulb-siphons, strainers, and pipettes. Attacking adults were collected using vials, and in 2020 the Centers for Disease Control and Prevention (CDC) light traps with dry ice were used on a limited basis to expedite collections. Collected specimens were microscopically identified using the taxonomic keys of Darsie and Ward (2005) and Carpenter and LaCasse (1955).
Overall, 339 county-level records were documented as part of this study. There were 139 records from peer-reviewed publications, 69 records from government documents or Texas DSHS data, 10 records from specimens in university collections, and 121 records from author field collections. The authors also collected an additional 136 species that had been previously reported as records (Table 1). Over the course of the study, the authors made 960 unique collections and identified 12,215 larvae, 2,375 females, and 2,441 males. Of the adults, 268 were captured as adults, and the remainder were reared from larvae or pupae and identified in the adult stage. The Texas DSHS data (2002–2020) were from 23 collection dates in Maverick (5), Sutton (14), Uvalde (1), and Val Verde (3) counties. This demonstrated the limited regional surveillance during this period and suggested more is needed to understand the potential for mosquito-borne disease in this region.
Table 1 displays the earliest known records for mosquito species collected in this region and for which the authors made at least 1 collection. Persons should expect to collect the species in the counties indicated. Of note is the first report of Cx. interrogator Dyar and Knab in this region. It was collected on November 11, 2020, in the city of Eagle Pass from a large wet area created by a broken water pipe. About 240 m away, a second population of Cx. interrogator was found in a depression along the edge of a lake lined with a dense stand of cattails, Typha sp.
The authors also collected Ae. aegypti from tree holes. While known to occur, tree holes are not a normal habitat for this species. In Rocksprings, Edwards County, Ae. aegypti were collected from 2 different Live Oak, Quercus virginiana Mill, tree holes in a city and county park, and in Eagle Pass, Maverick County, Ae. aegypti were collected twice from the same Berlandier Ash, Fraxinus berlandieriana DC, tree hole in a city park.
Mosquito species the authors did not collect in this region, but that were listed or found in peer-reviewed publications or government documents, are presented in Table 2. Of the 13 species listed in Table 2, only Anopheles crucians Wiedemann, Ae. dorsalis (Meigen), Ae. taeniorhynchus (Wiedemann), and Uranotaenia sapphirina (Osten Sacken) were collected multiple times by other sources. These species records may be valid but were not confirmed with a collection during this study. The remainder of the species in Table 2 were reported only once in the county indicated. These species may or may not exist in these counties, and additional surveillance is required to make that determination.
From the literature review, records from publications or documents began with Howard et al. (1915), which listed Cx. quinquefasciatus as being collected by F. C. Pratt in Kerrville (Kerr County) on May 30, 1906. This was followed by Howard et al. (1917), which listed records in Kerr (Anopheles punctipennis (Say)), Kimble (Psorophora cyanescens (Coquillett)), and Val Verde (An. pseudopunctipennis Theobald and An. punctipennis) counties. The same year, Dyar and Knab (1917) described an Ae. zoosophus Dyar and Knab female collected in Kerrville by F. C. Pratt on August 19, 1909. Dyar (1921a) reported mating swarms of Ae. aegypti (L.) and Cx. quinquefasciatus from Kerrville, and Dyar (1921b) described Cx. thriambus Dyar as a new species from collections along the Guadalupe River in Kerrville. Later, Dyar (1922) reported 2 additional records for Kerr County: Orthopodomyia signifera (Coquillett) and Ae. sticticus Meigen. Dyar (1922) also reported Cx. tarsalis in Val Verde County. In searching irrigated areas for malaria vectors, Barber et al. (1929) reported An. pseudopunctipennis and An. punctipennis in Val Verde County.
In 1951 Wilkins and Breland reported Or. alba Baker from Kimble County. Eads et al. (1951) reported multiple species from Edwards (11 species), Kerr (11), Kimble (27), Maverick (14), Sutton (19), Uvalde (18), and Val Verde (21) counties. In 1952, Buxton and Breland reared Ae. epactius Dyar and Knab, Ae. triseriatus (Say), Ae. zoosophus, Ae. trivittatus (Coquillett), and Ps. signipennis (Coquillett) from dry material collected in Kimble County and Ae. epactius from Val Verde County. Hedeen (1953) reported the collection of Ae. epactius with Ae. aegypti in an artificial container next to a store in Medina County. Later Hill et al. (1958) published the first county-level mosquito species checklist for Texas, which provided an initial baseline for mosquito species in this region and throughout the state.
In 1960 Breland reported a collection of Ae. triseriatus in Junction, Kimble County, and Easton et al. (1968) used malaise and animal baited traps to capture biting flies in Kinney County. They collected Ae. trivittatus, An. pseudopunctipennis, Cx. erraticus, Cx. quinquefasciatus, and Cx. tarsalis.
Zavortink (1972) included 2 records for Medina County, Ae. triseriatus and Ae. zoosophus, which were collected by L. T. Nielsen. Later Olson and Grimes (1974) collected 21 species in Dimmit and Maverick counties during the 1971 VEE epidemic. They combined the data for both counties, so for this study the number of specimens they collected were divided equally and considered as valid species for both counties. Fournier and Snyder (1977) and Fournier et al. (1989) published county-level mosquito species checklists, which updated the information in Hill et al. (1958). These later 3 documents were important because they added new data from their agencies and attempted to correlate old records with the original reporting source. Later Womack (1993) reported Ae. aegypti in Uvalde County and Ae. albopictus (Skuse) in Bandera, Kendall, Kerr, Kinney, Maverick, Medina, Uvalde, Val Verde, and Zavala counties.
Data were extracted from 18 documents of USAF published and unpublished data, but only 6 were used to document the earliest reported records in Val Verde County (USAF 1971, 1974, 1976; Muse et al. 1980, 1981; Swaby et al. 1983).
Sames et al. (2019) presented Cx. coronator Dyar and Knab records for all counties in this region. During this study, authors observed that the reported county records for Cx. stigmatosoma Dyar and Cx. thriambus were confounded for Texas. Sames et al. (2021) revised those data, which were then used in this study.
Curated specimens from this region were found in the Texas A&M University Insect Collection and the University of Texas Biodiversity Collection, and they were used to determine the earliest collection date for a species (Table 1). The mosquito collection at Sam Houston State University, Huntsville, TX, did not contain specimens from this region.
In conclusion, this study combined data from peer-reviewed publications or government documents, university and private collections, Texas DSHS data, and author collections to create a mosquito species list for 13 counties west of San Antonio. This list established a baseline from which others may find and reveal additional historic mosquito surveillance documents or add to the species list through active collections. This comprehensive mosquito species list will be useful to future regional studies, as a resource for public health officials, and for presenting mosquito geographical distributions in state and national publications.
We thank Clarke Mosquito Control Products, Inc. for their assistance with the publication costs of this article. We also thank the many property owners or managers who granted permission to collect mosquito larvae from various aquatic habitats on their property. Also, we thank the participants in the Texas DSHS Arbovirus Surveillance Program for their diligence in protecting the people in their communities and the Texas A&M AgriLife County Extension personnel (Brett Allen, Pascual Hernandez, and Marcel Valdez) who helped coordinate property access and assisted with collections. We are grateful to the family and friends that assisted with the collections: Brian Byrd, Steven Hogue Jr., Gabriel Rodriquez, Martha Sames, and Suzanne Whitworth. A big thanks to Nathan Burkett-Cadena for his consultations on mosquito identifications. We also thank Karen Wright (Texas A&M University Insect Collection, TAMUIC), Alex Wild (University of Texas Insect Collection), and Jerry Cook (Sam Houston State University Insect Collection) for assistance in reviewing their university's mosquito collections. We thank mapchart.net for allowing access and use of their online mapping capabilities in the creation of Fig. 1.
PO Box 547, Leakey, TX 78873.
2911 Bandera Hwy, Kerrville, TX 78028.
Arbovirus-Entomology Team, Laboratory Services Section, Texas Department of State Health Services, 1100 W. 49th Street, Austin, TX 78756.