Supat Sucharit

In vitro studies on the sensitivities of Plasmodium falciparum in Thailand to pyrimethamine and proguanil

The susceptibility to pyrimethamine and proguanil of a strain of Plasmodium falciparum from Thailand was assessed by using blood from the same patient cultured by two different techniques. Irrespective of the technique used, the strain of P. falciparum appeared more sensitive to proguanil than to pyrimethamine.

Studies on oviposition characteristics of Mansonia (Mansonioides) mosquitoes in southern Thailand

Oviposition characteristics of Mansonia (Mansonioides) mosquitoes were studied to assess future possibilities for their control. Special emphasis was given to the study of the factors, especially the host plant species, which guide the gravid females towards the oviposition site. Initially, egg dispersal throughout the breeding place was assessed by comparing egg densities between so-called areas of 100-200 m2, each characterized by reasonable homogeneity in its flora. Some of these areas were preferred by gravid females, indicating an aggregative type of distribution. There was no evidence that the attractiveness of areas was correlated with the availability of preferred host plants. Egg dispersal within areas was then studied using randomly chosen plots of 1 X 1 m or 15 X 15 cm as sampling units. This again revealed aggregative egg distributions which could be fitted to a negative binomial expectation. The amount of visible water surface, rather than the availability of host plants, appeared to determine the attractiveness of the plots. The dispersal within 1 m2 experimental plots containing the host plants Pistia, Eichhornia and Salvinia was then investigated and this showed clearly that specific levels of attractiveness of plant species influenced egg dispersal. These levels were modified by (i) the presence of grasses in the immediate surroundings, (ii) features of grass growth and (iii) the type of host plant arrangement. It was concluded that the factors responsible for egg aggregations vary with the size of the samples compared, and that the host plant species plays a significant role only for the distribution within quite small units of the breeding place.

A small scale field trial with Temephos (Abate) for the control of four species of Mansonia (Mansonioides) (Diptera: Culicidae) in Thailand

A 60-week control experiment with Temephos (Abate) against a largely isolated population of Mansonia annulata, Ma. annulifera, Ma. indiana and Ma. uniformis was carried out in a pool of 1.2 ha area and average depth of over 2 m in southern Thailand. Floating paper tea bags containing 24 g of 1% Abate sand granules were applied in two rounds at a density of 1 bag 4 m-2. Each round consisted of five applications at intervals of 13 days. During the application rounds mosquito larvae disappeared completely from the pool. This apparent effect of Abate was confirmed by bioassays made with pool water and larvae of Culex quinquefasciatus. Inactivation of Abate was linear during one week, with a slope of 5.8% per day. Adult densities dropped during the application rounds and, over a period of 48 weeks, were 78-85% less than during the corresponding time of the preceding reference year. The annual pattern of adult abundance that normally shows distinct seasonal peaks was strongly altered, although meterological data were comparable to the reference year.