INTRODUCTION

The Henderson American pointy mosquito, Aedes (Protomacleaya) hendersoni Cockerell, also known as one of the eastern tree-hole mosquitoes, was originally described by the American entomologist Theodore Dru Alison Cockerell (1866–1948) as a variety of the other species also commonly named eastern tree-hole mosquito, Ae. triseriatus (Say), from specimens collected in the vicinity of Douglas, Wyoming, USA (Cockerell 1918); subsequently, Ae. hendersoni was synonymized under the name Ae. triseriatus by Dyar (1922, 1928) and until 1960, Ae. hendersoni was considered as either synonym or subspecies of Ae. triseriatus (Hedeen 1963). In 1960, Ae. hendersoni was elevated from synonymy to the rank of specific valid name by Breland (1960), based on the observation of external characters of reared females, larvae, and chromosome complement comparison. Further differences between Ae. hendersoni and Ae. triseriatus females were later observed on the tarsal claws (Harmston 1969) and host selection; although Ae. hendesoni fed mainly on tree squirrels and raccoons, Ae. triseriatus fed predominantly on chipmunks and deer (Nasci 1982). A complete description of all life stages, except eggs of Ae. hendersoni and Ae. triseriatus, and a revision of their taxonomy, distribution, and bionomics was provided by Zavortink (1972), while the eggs of Ae. hendersoni were described and compared with the Ae. triseriatus eggs by Linley and Craig (1993). Aedes hendersoni was later placed into the genus Ochlerotatus sensu auctorum, based on phylogenetic analyses of all life stages on the Aedini tribe (Reinert et al. 2004, 2006, 2008, 2009), and, subsequently, re-stored in the genus Aedes by Wilkerson et al. (2015). Aedes hendersoni belongs to the Triseriatus group (Aedes: Protomacleaya), which also includes the species Ae. brelandi Zavortink, Ae. triseriatus, and Ae. zoosophus Dyar and Knab (Zavortink 1972, Taylor 1990).

Species in the Triseriatus group are distributed predominantly in the Nearctic region, Ae. triseriatus and Ae. hendersoni occupy vast geographical ranges, and much of North America is inhabited by one or both species. Aedes hendersoni occurs abundantly in the eastern United States and small portions of southern Canada, where it was first reported in the provinces of British Columbia (Zavortink 1972), Ontario and Quebec; and, Saskatchewan (Trimble 1972). In the United States, Aedes hendersoni extends much further west than Ae. triseriatus, reaching the southeastern region of British Columbia and eastern Washington and Oregon in the north as well as the northern regions of Nevada and Utah, eastern Colorado and New Mexico, and mid-northern Texas to the south, although it is absent in peninsular Florida, and without records in the extreme southern Texas (Darsie and Ward 2005, Fitzgerald and Livdahl 2019) (Fig. 1).

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MATERIALS AND METHODS

Samples collection and curation

Adult mosquitoes were collected monthly at dusk and night hours (17:00–22:00 h), and occasionally at morning hours (08:00–10:00 h), using three Centers for Disease Control and Prevention (CDC) miniature light traps (John W. Hook Company, Gainesville, FL, USA) with a 0.95 watts incandescent light baited with 3–5 drops of octanol on 1–2 cotton balls per trap. Two Shannon traps containing humans (Fig. 2) were also deployed 100 m apart from CDC light trap collection sites. In addition, host-seeking mosquitoes were caught using mechanical aspirators. Collected specimens were killed in situ using chloroform vapors, labeled, and transported to local labs. Voucher specimens were curated and deposited in 2 Mexican collections repositories: The Agronomy School of the Autonomous University of Nuevo León (FA-UANL), located in Monterrey, Nuevo León and the Antonio Narro Autonomous Agrarian University-Laguna Unit (UAAAN-UL), located in Torreón, Coahuila. Specimens were morphology identified using the keys of Schick (1970), Zavortink (1972), and Darsie and Ward (2005).

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RESULTS

Fourteen Ae. hendersoni females were caught at Cascadas de Guadalupe using Shannon traps deployed in two collection sites from August to September 2020 and from March to April and July 2021. Only 7 Ae. hendersoni females were caught with mechanical aspirators at the same collection sites. However, none Ae. hendersoni was caught in the CDC light traps. Other mosquito species were also caught: Anopheles pseudopunctipennis Theobald, Ae. amateuri Ortega and Zavortink, Ae. trivittatus (Coquillett), Ae. amabilis Schick, Ae. podographicus Dyar and Knab, Ae. triseriatus, Ae. (Protomacleaya) sp., Ae. aegypti (L.), Ae. albopictus (Skuse), Haemagogus equinus Theobald, Psorophora ferox (von Humboldt), Culex coronator Dyar and Knab, Cx. interrogator Dyar and Knab, and Cx. nigripalpus Theobald. Seven and 11 Ae. hendersoni females were also caught at El Salto using mechanical aspirators in October 2020 and 2023 along with other species: Ae. quadrivittatus (Coquillett), Ae. trivittatus, Ae. podographicus; and Ae. quadrivittatus, Ae. triseriatus, Ae. amabilis, Ae. albopictus, and Wyeomyia mitchellii (Theobald), respectively (Table 1).

Table 1.Total number of Aedes hendersoni females collected in Nuevo León, México along with other associated species caught in 2020–2023.

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The Ae. hendersoni (GenBank accession number: MG242473.1) sequences (n = 6) of this study were compared with Ae. hendersoni sequences (n = 2) downloaded from the GenBank of National Centre for Biotechnology Information (NCBI), and with sequences (n = 20) from specimens belonging to the subgenus Protomacleaya collected in Nuevo León such as Ae. amabilis (MT999244.1) (n = 7), Ae. podographicus (MT552480) (n = 6), and Ae. triseriatus (JX259710.1 and MG242523.1) (n = 6), and an outer group Cx. pipiens L. (CYTC704) from Greece (n = 1). The PCR amplification, sequencing, Basic Local Alignment Search Tool (BLAST), and phylogenetic analysis of the COI gene revealed that the specimens examined belong to Ae. hendersoni, clustering and sharing 97.72% identity with Ae. hendersoni (MG 242498.1) (Fig. 3). The COI sequences of Ae. hendersoni have been deposited in the NCBI GenBank with accession number MG242473.1.

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DISCUSSION

The adult female of Ae. hendersoni are readily recognized among species of the Triseriatus group by having tarsal segments 1–5 of all legs entirely dark scaled; bristles of the anterior portion of mesoscutum relatively numerous and well developed; light scaling of fossa usually extensive and extending mesad of anterior dorsocentral bristles, the scaling more or less bordered on all sides by conspicuous setae lightly to moderately pigmented (Fig. 4); and postspiracular scale patch absent to small (Zavortink 1972). Further differences between Ae. hendersoni and Ae. triseriatus females were observed: in Ae. hendersoni, some few pale scales on the anterior portion of mesoscutum are always present, and these can form a slightly and narrow complete acrostichal line of pale scales, reaching the pre-scutellar area, which is present in some specimens observed. Nevertheless, in most of them, this acrostichal line is absent (Fig. 4). Figure 4 shows the presence of narrow and complete dorsocentral pale scales. In Ae. triseriatus, there is no sign of any pattern or presence of pale scales on the acrostichal or dorsocentral areas in the observed specimens. These differences were observed and documented by Zavortink (1972) from American “Western” populations of Ae. hendersoni. Differences between Ae. hendersoni and Ae. triseriatus are more noticeable in the larval stage, in Ae. hendersoni by having acus of siphon well detached from the base of siphon, anal gills about the same length and much longer than ninth segment, and in general, the light color of body integument (Breland 1960, Grimstad et al. 1974).

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Aedes triseriatus is the primary vector of La Crosse (LAC) virus, responsible for encephalitis, especially in young children (Watts et al. 1973, Reno et al. 2000), but Ae. hendersoni is incompetent as vector because of its salivary gland barrier to LAC virus (Watts et al. 1975, Grimstad et al. 1985, Paulson and Grimstad 1987, Paulson et al. 1992). Routine vector surveillance of Ae. triseriatus and Ae. hendersoni is paramount; although the role of Ae. hendersoni as an inefficient vector of LAC virus is well understood, that of other closely related species as vectors of LAC virus remains to be fully elucidated. The LAC virus has not been reported yet in Mexico because encephalitis, as a vector borne disease, is neglected. Although Aedes hendersoni is not recognized as a dangerous or incriminated vector of public health importance, it is associated with being a human nuisance in tourist areas elsewhere.

By adding Ae. hendersoni to the mosquito fauna of Mexico, currently there are 253 species, of which, 69 species are of Nuevo León. Voucher specimens are available in 2 Mexican mosquito collection repositories: the Collection of Arthropods with importance in One Health of the FA-UANL, Nuevo León, with reference numbers NL-02-240820, NL-02-270820, NL-03-220920, NL-04-240920, NL-04-230920, 01-220321-CS, 02-220321-CS, 07-220321-CS, 01-230321-CS, 02-230321-CS, 02-280421-CS, 04-260521-CS, 09-240621-CS, 09-280721-CS, 09-250621-CS, 05-250621-CS, 04-270721-CS, 05-270721-CS; and UAAAN-UL of Coahuila, with reference numbers 01271023-RS and 01281023-RS; collection code: Tesis_camada_10.