DIFFERENTIAL BIO·ECOLOGY OF ANOPHELINE SIBLING SPECIES: A RELEVANCE TO MALARIA CONTROL IN SRI LANKA

Abstract

Human intervention by various means has altered natural ecosystems and thus paved wayfor emergence of new vectors and their propagation leading to the spread of malaria worldwide. Vector ecological studies have been undertaken in order to locate risk areas for. malaria and to formulate appropriate strategy for vector control. The prevalence andabundance of mosquito immature stages in various breeding sites reflect the ovipositionreference of females and it can be attributed at inter specific and intraspecific levels.Knowledge, especially at intraspecific level, on bio-ecology of vectors is an essentialprerequisite for formulating effective environmental management interventions for thecontrol of malaria.

Morphologically more or less similar but reproductively isolated members of a taxon aretermed sibling species and the taxon are species complex. Sibling species exhibitdifferences with respect to feeding and resting preference, rate of development of resistanceto insecticide, susceptibility to parasites and seasonal prevalence.

Among known malaria vectors in Sri Lanka, Anopheles culicifacies, the major vector ofmalaria, An. Subpictus and An. Annularis, the subsidiary vectors arc reported to be existingas species complex in the Indian subcontinent. Studies on the biononiics of the two siblingspecies B am! E of A/I. Culicifacies in Sri Lanka reveal that these two sympatricpopulations arc diverged in certain bio- ecological aspects which are essential forimplementing a successful vector control program. Laboratory infective studies showedthat species E could support the extrinsic cycle of Plasmodium I'ivax and P. falciparum.Studies on the age structure of species Band E revealed that species E has entered theepidemiologically dangerous age. Both siblings showed differential susceptibility toMalathion. Studies on the limnological characterization of larval breeding sites of speciesD and E showed that species E prevailed in variety of breeding habitats, an indication ofhigh level of adaptive variation of species E. Sibling species status of An. Annularis in SriLanka is yet to be revealed. A study on the sibling species of All .• Subpitus from a locality inN0I1h Western province of Sri Lanka revealed that species B is predominant in coastal am!species C in inland areas.