Phylogeny of the nominotypical subgenus of Culex (Diptera: Culicidae): insights from analyses of anatomical data into interspecific relationships and species groups in an unresolved tree

The insupportable validity of mosquito subspecies (Diptera: Culicidae) and their exclusion from culicid classification

Beginning about 80 years ago, the recognition of morphological varieties of mosquitoes was gradually replaced by the recognition of subspecies. As an examination of revisionary and detailed taxonomic studies of mosquitoes clearly shows, subspecies are untenable concepts which have been synonymized with nominotypical forms or recognized as distinct species. Thus, from our perspective, subspecies is not a functional or practical taxonomic rank. Consequently, in this study we critically assessed the taxonomic status of the 120 nominal taxa distinguished as subspecies before now to determine whether they should be recognized as separate species or synonymous names. As a result, 96 subspecies are formally elevated to specific rank, 22 are relegated to synonymy with nominotypical forms, one is considered a nomen dubium, one a species inquirenda and the names of four nominal species regarded as synonyms are revalidated. The subspecies and their new status are listed in a conspectus. The revalidated species include Anopheles argentinus (Brèthes, 1912), from synonymy with An. pseudopunctipennis Theobald, 1901c; An. peruvianus Tamayo, 1907, from synonymy with An. pseudopunctipennis as nomen dubium; Culex major Edwards, 1935, from synonymy with Cx. annulioris consimilis Newstead, 1907; and Trichoprosopon trichorryes (Dyar & Knab, 1907), from synonymy with Tr. compressum Lutz, 1905. Additionally, the type locality of Anopheles sergentii Theobald, 1907 is restricted to El Outaya, Biskra Province, Algeria. A complete list of species to be retained, added to or removed from the Encyclopedia of Life, with a few corrections, is provided.

Revalidation of Phalangomyia Dyar & Knab as a subgenus of Culex L. (Diptera: Culicidae) based on morphological and molecular evidence

Culex apicinus Philippi, 1865 and its synonyms, Phalangomyia debilis Dyar & Knab, 1914, Cx. escomeli Brèthes, 1920 and Cx. alticola Martini, 1931, were re-examined employing molecular and morphological phylogenetic methods. Archival and fresh specimens were used for morphological diagnosis and to generate fragments of two single-copy nuclear genes (CAD, HB) and one mitochondrial gene (COI). Additional sequences of Cx. apicinus and species of the subgenus Culex of Culex Linnaeus, 1758 and other subgenera of the genus were obtained from GenBank for molecular analysis. Diagnostic morphological characteristics of Cx. apicinus and other species of the subgenus Culex were contrasted. Phylogenetic relationships were generated using DNA sequences of protein coding genes under both Maximum Likelihood and Bayesian approaches. Culex apicinus showed unique morphological traits that allow its classification in a separate subgenus. The subspecific status is supported by its recovery as a monophyletic clade within the genus Culex based on morphological and molecular characters. The synonymous Phalangomyia debilis provides an available subgeneric name. Consequently, Phalangomyia Dyar & Knab, 1914 is resurrected from synonymy with Culex Linnaeus, 1758 as a monobasic subgenus of Culex.

Ribosomal RNA (rRNA) sequences from 33 globally distributed mosquito species for improved metagenomics and species identification

Total RNA sequencing (RNA-seq) is an important tool in the study of mosquitoes and the RNA viruses they vector as it allows assessment of both host and viral RNA in specimens. However, there are two main constraints. First, as with many other species, abundant mosquito ribosomal RNA (rRNA) serves as the predominant template from which sequences are generated, meaning that the desired host and viral templates are sequenced far less. Second, mosquito specimens captured in the field must be correctly identified, in some cases to the sub-species level. Here, we generate mosquito rRNA datasets which will substantially mitigate both of these problems. We describe a strategy to assemble novel rRNA sequences from mosquito specimens and produce an unprecedented dataset of 234 full-length 28S and 18S rRNA sequences of 33 medically important species from countries with known histories of mosquito-borne virus circulation (Cambodia, the Central African Republic, Madagascar, and French Guiana). These sequences will allow both physical and computational removal of rRNA from specimens during RNA-seq protocols. We also assess the utility of rRNA sequences for molecular taxonomy and compare phylogenies constructed using rRNA sequences versus those created using the gold standard for molecular species identification of specimens-the mitochondrial cytochrome c oxidase I (COI) gene. We find that rRNA- and COI-derived phylogenetic trees are incongruent and that 28S and concatenated 28S+18S rRNA phylogenies reflect evolutionary relationships that are more aligned with contemporary mosquito systematics. This significant expansion to the current rRNA reference library for mosquitoes will improve mosquito RNA-seq metagenomics by permitting the optimization of species-specific rRNA depletion protocols for a broader range of species and streamlining species identification by rRNA sequence and phylogenetics.

Species-Specificity in Thermopreference and CO2-Gated Heat-Seeking in Culex Mosquitoes

Combining thermopreference (Tp) and CO2-gated heat-seeking assays, we studied the thermal preferendum and response to thermal cues in three Culex mosquito species exhibiting differences in native habitat and host preference (e.g., biting cold and/or warm-blooded animals). Results show that these species differ in both Tp and heat-seeking behavior. In particular, we found that Culex territans, which feed primarily on cold-blood hosts, did not respond to heat during heat-seeking assays, regardless of the CO2 concentration, but exhibited an intermediate Tp during resting. In contrast, Cx. quinquefasciatus, which feeds on warm blooded hosts, sought the coolest locations on a thermal gradient and responded only moderately to thermal stimuli when paired with CO2 at higher concentrations. The third species, Cx. tarsalis, which has been shown to feed on a wide range of hosts, responded to heat when paired with high CO2 levels and exhibited a high Tp. This study provides the first insights into the role of heat and CO2 in the host seeking behavior of three disease vectors in the Culex genus and highlights differences in preferred resting temperatures.