Culex (Culex) trifilatus Edwards

Harbach, Ralph E. & Wilkerson, Richard C., 2023, The insupportable validity of mosquito subspecies (Diptera: Culicidae) and their exclusion from culicid classification, Zootaxa 5303 (1), pp. 1-184 : 92

Culex (Culex) trifilatus Edwards

subspecies aenescens Edwards, 1941 —original combination: Culex (Culex) trifilatus ssp. aenescens . Distribution: Eritrea ( Mara 1945), Uganda ( Edwards 1941).

subspecies trifilatus Edwards, 1914 —original combination: Culex trifilatus . Distribution: Angola, Cameroon, Democratic Republic of the Congo, Ethiopia, Gabon, Guinea, Kenya, Madagascar, Malawi, Mozambique, Republic of the Congo, Republic of South Africa, South Sudan, Sudan, Tanzania, Uganda, Zimbabwe, Zambia ( Wilkerson et al. 2021).

Culex trifilatus was descried by Edwards (1914) based on adult males and females collected in Kabete, Kenya. In 1941, he described subspecies aenescens from adults captured in the Toro District of Uganda. Subspecies aenescens was distinguished principally from the type form in having seta c of the subapical lobe of the male gonocoxite as long as seta b (seta c is shorter than b in the type form), setae d and e absent (both present in the type form) and seta f very slender (broad and flattened in the type form). However, the illustrations of the genitalia provided by Edwards (1941) clearly indicate that the two laterally bent projections of the lateral plate are more slender, the dorsal one is tapered and pointed, and the dorsal arm is narrower and longer in subspecies aenescens (the dorsal projection is broadened apically in the nominate subspecies). The larva of subspecies aenescens was described by Hopkins (1952) from many specimens collected in the Toro District. The larva of the nominate subspecies was not known until it was described by Ribeiro et al. (1982) based on specimens from Angola (Ribeiro & da Cunha Ramos 1980) and Tanzania ( V. N. Danilov). As described by these researchers, larvae of subspecies aenescens differ from those of the type form as follows: Seta 5-C with 3 branches (4 or more in the type form); siphonal seta 1-S comprised of 3 pairs of alternating setae with 2–5 branches (with 3–9 branches in the type form); seta 1-X single or double (always single in the type form); dorsal pair of anal papillae 1.5 times as long as the ventral pair, which are about as long as the saddle (dorsal pair 3 times as long as the ventral pair in the type form, but the ventral pair are only about half as long as the saddle).

Ribeiro et al. (1982) stated that the two subspecies are allopatric based on then present knowledge of their geographical distributions. This is apparently incorrect as both forms are recorded from localities in Uganda and a footnote in Hopkins (1952) provided by P. F. Mattingly indicates that Mara (1945) recorded the presence of subspecies aenescens in Eritrea. Stone et al. (1959), and later catalogs, indicate that the type form has been found in Ethiopia and Sudan, but without identifying the sources of those records and whether they are based on adult or larval mosquitoes. Assuming the identifications are correct, it seems likely that the two subspecies occur in sympatry in northeastern areas of the Afrotropical Region.

It is an undeniable fact that most species of Afrotropical Culex are incompletely (inadequately) described and illustrated or otherwise only superficially known. As a result of critical revisionary studies, it is known that many currently recognized species of the genus are distinguished by a combination of seemingly minor differences in individual life stages, e.g. species of the Oriental Vishnui Group ( Sirivanakarn 1976), and some nominal species thought to be conspecific have been found to be distinct species with very similar male genitalia that exhibit distinctive minor differences, e.g. Cx. bidens Dyar, 1922 and Cx. interfor Dyar, 1928 ( Harbach et al. 1986). It is well known that male genitalia generally provide a better means for distinguishing species than any other morphological characters, especially members of the genus Culex . Evolution of genital form is thought to be involved in the origin of species and the reproductive isolation between species. Thus, the differences in the male genitalia noted above would alone provide prima facie evidence of separate species; however, those differences coupled with the larval differences and the probable sympatry of the two forms further strengthens the likelihood that aenescens is a valid species. For these reasons, we feel justified in formally recognizing this nominal subspecific taxon as a distinct species: Culex (Culex) aenescens Edwards, 1941 . Culex aenescens is currently listed as a species in the Encyclopedia of Life.