BIOLOGY AND VECTOR COMPETENCE OF THE ANOPHELINE MOSQUITOES OF MYANMAR WITH SPECIAL CONSIDERATION OF ANOPHELES DIRUS

Abstract A brief critical review has been made of the material concerning malaria available from the second world war. In addition a short description has been given of the war-time anti-malaria organization in Myanmar. The physical features of Myanmar, in relation to the distribution of malaria in seven natural sub-divisions have been briefly discussed. In part I: thirty-seven species of anopheline mosquitoes recorded in Myanmar have been considered in detail with particular reference to the distribution, breeding sites, seasonal prevalence, adult behaviour and their vector competence. Some general aspects of anopheline behaviour are discussed. Classification has been made of all recorded species in relation to malaria transmission and the distribution of malaria in Myanmar as follows: dissection records, feeding habits, distribution, seasonal prevalence, evidence from other sources. In Myanmar, the mosquitoes responsible for regular or annual malaria transmission (primary vectors) are (i) Anopheles dirus and (ii) Anopheles minimus. Predominatly cattle-feeders which may under abnormal conditions, feed on man. Often abundant and capable, therefore, of transmitting malaria (secondary vectors) are (iii) Anopheles aconitus (iv) Anopheles annularis (v) Anopheles culicifacies (vi) Anopheles sinensis (vii) Anopheles jeyporensis (viii) Anopheles maculatus (ix) Anopheles philippinensis (x) Anopheles sundaicus. Vector competence of these ten species are also described. Part II: mainly concerns genetic studies of Anopheles dirus from the Mudon area. An. dirus normally occurs in the forest and forest fringes where it transmits malaria efficiently. Changes in the ecology of an area induced by new developments, like deforestation, construction of dams and irrigation projects may have profound or indirect effects upon vector occurrence because of the creation of suitable ecotypes for the completion of its life cycle. Thus, the dangerous vector An. dirus has invaded human settlements. This typical forest breeder could successfully adapt and spread all over Mudon. It is potentially hazardous to public health so as to provide knowledge for further research and control needed in this area. Thus, the purpose of the study is to establish the degree of genetic divergence (similarity) between the three topographically different populations of An. dirus: An. dirus 1 (from forested areas), An. dirus 2 (from rubber plantation areas) and An. dirus 3 (from domestic areas). Field-collected specimens (both adults and larvae) were used in horizontal ultrathin agarose electrophoresis for identification. A more detailed analysis was performed in the present study using eleven gene enzyme systems (comprising twelve presumptive loci) to determine the degree of genetic differentiation among these three populations of An. dirus in comparison with An. maculipennis from Mannheim, Germany and An. stephensi from Indonesia, provided by Bayer AG, Leverkusen (breeding stock). Based on the data obtained from the migration of enzymes, the following values were computed in each population: relative frequencies of alleles and genotypes, confidence and the variances of allele frequencies, conformity to expectations of the Hardy-Weinberg rule with X2 (chi square) values, the degree of heterozygosity and polymorphism, Nei`s genetic distances and the values of genetic similarity between the species. Phylogenetic relationship between the respective population pairs among these gene pools have been demonstrated by dendrogram using the Kitsch program. This dendrogram clustered the populations in two forms; three An. dirus population groups together in two groups. The first group (population 1: An. dirus 1 from forested area and population 2: An. dirus 2 from rubber plantation area) to be clustered are those with the smallest genetic distance. Populations of second group are developed from the first group and population 3 (An. dirus 3 from domestic area). These two groups of An. dirus are then combined and taken to be a single group. The populations of the third group entity are from another cluster for An. dirus combined group and population 4 (An. stephensi from Indonesia). The genetic identity values between these three populations of An. dirus ranged from 0.9978 to 0.9999 which is the generally accepted range for conspecific populations. The high values of genetic similarity indices suggest that natural populations of An. dirus in Mudon area share an undifferentiated gene pool. The very low genetic distance D (between 0.0001 to 0.0022) also indicate that these three populations of Anopheles dirus from Mudon area are parts of a metapopulation without measureable adaptations due to selective conditions in ecologically different breeding sites