Nine and 11 isolines of Anopheles argyropus and Anopheles pursati, respectively, were established from individual females collected from cow-baited traps, and the characteristics of metaphase chromosomes were investigated in their F1-progenies. As determined by the different amounts of extra heterochromatin on sex chromosomes, 2 types of X (X1, X2) and Y (Y1,Y2), and 2 types of X (X1, X2) and 3 types of Y (Y1, Y2, Y3) chromosomes were obtained from An. argyropus and An. pursati, respectively. These types of sex chromosomes comprised 2 [Forms A (X1, Y1) and B (X1, X2, Y2)] and 3 [Forms A (X1, X2, Y1), B (X1, X2, Y2) and C (X2, Y3)] karyotypic forms of An. argyropus and An. pursati, respectively. All karyotypic forms acquired from An. pursati are new one that were discovered in this study, of which Forms A, B and C were found generally in Chiang Mai Province, while only 1 isoline of Form B was obtained in Ratchaburi Province. Form A was recovered from An. argyropus only in Ubon Ratchathani Province, whereas Form B from that species was found commonly in both Ubon Rathchathani and Nakhon Si Thammarat Provinces. Crossing experiments among the 2 and 3 isolines representing 2 and 3 karyotypic forms of An. argyropus and An. pursati, respectively, indicated genetic compatibility in yielding viable progenies and synaptic salivary gland polytene chromosomes through F2-generations. The conspecific natures of these karyotypic forms in both species were further supported by very low intraspecific sequence variations (average genetic distance: An. argyropus = 0.003-0.007, An. pursati = 0-0.005) of ribosomal DNA (ITS2) and mitochondrial DNA (COI and COII).

Some species of the Anopheles dirus species complex are considered to be highly competent malaria vectors in Southeast Asia. Anopheles dirus is the primary vector of Plasmodium falciparum and P. vivax while An. cracens is the main vector of P. knowlesi. However, these two species are difficult to distinguish and identify based on morphological characters. Hence, the aim of this study was to investigate the potential use of antennal sensilla to distinguish them. Large sensilla coeloconica borne on the antennae of adult females were counted under a compound light microscope and the different types of antennal sensilla were examined in a scanning electron microscope. The antennae of both species bear five types of sensilla: ampullacea, basiconica, chaetica, coeloconica and trichodea. Observations revealed that the mean numbers of large sensilla coeloconica on antennal flagellomeres 2, 3, 7, 10 and 12 on both antennae of both species were significantly different. This study is the first to describe the types of antennal sensilla and to discover the usefulness of the large coeloconic sensilla for distinguishing the two species. The discovery provides a simple, reliable and inexpensive method for distinguishing them.