Anopheles culicifacies sibling species B and E in Sri Lanka differ in longevity and in their susceptibility to malaria parasite infection and common insecticides

Abstract

Members of the Anopheles culicifacies Giles complex (Diptera: Culicidae) are well established as the predominant vectors of malaria in Sri Lanka. Until recently, only sibling species B was reported to be present in Sri Lanka, which was surprising as species B is a poor vector of malaria in India. This was clarified by the identification through Y-chromosome morphology that what was reported as B on the island is really a mixture of B and E. The fecundity, longevity and insecticide resistance of B and E are of relevance to malaria transmission and its control and are reported in this study. The mean egg production of these two sibling species did not differ significantly. The mean age of wild mosquitoes was assessed by the Polovodova technique of observing ovarian dilatations. More of species E than B had three or more dilatations, i.e. had reached an age at which sporozoites could have developed to maturity, although the difference between the species was of borderline significance. Following feeding on Plasmodium vivax or Plasmodium falciparum infected blood, some females of species E developed oocysts but none of species B did so. Both sibling species were found fully susceptible in laboratory tests to lambdacyhalothrin and deltamethrin, but resistant to DDT and partially resistant to malathion.

Variations in susceptibility to common insecticides and resistance mechanisms among morphologically identified sibling species of the malaria vector Anopheles subpictus in Sri Lanka

“…Inland localities are defined as being ≥ 2.5 km from the coast. Both cattle-baited hut (CBHC) and cattle-baited net (CBNC) collection techniques were used to collect blood-fed adult mosquitoes [22]. …”

“…Facilities and expertise were not available for determining polytene chromosome banding patterns during this investigation and therefore only morphological characteristics were used in identification. Identified blood-fed females were maintained individually and single female F 1 progenies were raised as described previously [22]. Sibling species status of females laying eggs was determined through the reported number of ridges in the floats of egg that characterize the different sibling species in India [10].…”

“…A previous study on the differential susceptibility of the two members of the An. culicifacies complex present in Sri Lanka showed that vector species E was more resistant to malathion than the non-vector species B [22]. Another study that investigated insecticide resistance mechanisms among An.…”

On the road to eliminate malaria in Sri Lanka: lessons from history, challenges, gaps in knowledge and research needs

“…culicifacies [10,57-59], which is considered as a zoophilic and indoor-resting mosquito. However, other anopheline species, such as Anopheles subpictus, Anopheles annularis have also been incriminated as vector species in the country [12,60,61].…”

“…culicifacies mosquitoes [10,62] more recent evidence points to its ability to adapt to variable conditions, such as increasing salinity in water [15] and even polluted water [63], which are important factors to consider from a vector control perspective. The role of different sibling species within the Anopheles species complexes in malaria transmission and their biological properties have also been reported through studies conducted in the endemic zones of the country [13,59,64]. Such knowledge regarding bio-ecological traits of sibling species, though still limited, has alerted the community of its potential implications and relevance of such considerations for the design and implementation of effective vector control measures, particularly during this critical phase of malaria elimination.…”