Confirmation of Culex (Culex) tritaeniorhynchus summorosus (Diptera: Culicidae) as a separate species

Background objectives: Culex tritaeniorhynchus, a member of Cx. vishnui subgroup, is an important vector of Japanese encephalitis (JE) virus. Cx. tritaeniorhynchus summorosus considered as a variety or subspecies of Cx. tritaeniorhynchus, has been studied in detail to settle its taxonomic status. Surveys for the collection of Cx. tritaeniorhynchus from Chandigarh and adjoining areas have established the availability of Cx. summorosus from this area. Methods: For the present investigation, collections have been made from Chandigarh and its adjoining areas (up to 60 km) for procuring the material. The detailed morphology including scanning electron microscopy of immatures (eggs and larvae) and adults of Cx. tritaeniorhynchus and Cx. summorosus has been studied and compared. Further, the interbreeding experiments of the two species were also conducted and efforts had been made to allow cross- breeding among the members of these two species. Results: Comparison of egg, larval and adult morphology of Cx. summorosus with the parental species Cx. tritaeniorhynchus under the light and electron microscope, revealed significant differences. Moreover, these two species have also been found to be reproductively isolated as indicated by laboratory experiments. This settles the controversy on the status of Cx. summorosus and confirms its status as a distinct species. Interpretation conclusion: The study establishes that the two species show considerable number of differences which are sufficient to consider them as separate species rather than subspecies or variant of Cx. tritaeniorhynchus. Furthermore, the absence of interbreeding between these two again confirms their separate specific status according to biological species concept. But, it is yet to ascertain whether Cx. summorosus is a vector of Japanese encephalitis like Cx. tritaeniorhynchus or not.