Comparative morphometry, morphology of egg and adult surface topography under light and scanning electron microscopies, and metaphase karyotype among three size-races of Fasciola gigantica in Thailand.

Comparative morphometry of eggs and adults under light microscope, and morphology of adults under scanning electron microscope (SEM) were undertaken in the three size-races (< 25 mm, 25-35 mm, > 35 mm) of Fasciola gigantica (Thailand strain). Morphometric examination revealed intraspecific variation with respects to the dimensions of eggs and adults, whereas surface topography of the three size-race adults under SEM was morphologically similar. The observations on mitotic metaphase chromosomes of spermatogonial cells from testes of the three size-races revealed 2n=20 (diploid type), and no karyotypic difference was observed among them. The meiotic metaphase chromosome was 10 bivalents in primary spermatocyte in diplotene to diakinesis, and many mature spermatozoa were seen in the testicular preparations.

Studies on the Japanese encephalitis vectors in Amphoe Muang, Chiang Mai, Northern Thailand.

From February 1987 to January 1988, biological and ecological studies were made to obtain the basic knowledge of Japanese encephalitis vectors, Culex tritaeniorhynchus, Cx. gelidus, and Cx. fuscocephala, in Amphoe Muang, Chiang Mai, northern Thailand. The following results were found. Peaks in the population densities of the vectors as measured four times a month, by UV-light trap and human-baited trap collections, occurred during rainy season. The JE vectors in rural areas showed a sharp rise in the population in July when most of the rice fields were ploughed and a marked decline in mosquito population densities occurred after transplanting in August when the fields were flooded. The average number of larvae plus pupae per m2 in rice fields was highest in July when the fields were ploughed, but in the period from transplanting to harvesting (August to November), the densities were very low. Daily survival rates of the adult females, as estimated from parous rates, were mostly as high as 0.7 throughout the year.