Study on bionomics of principal malaria vectors in Kratie province, Cambodia.

A cross-sectional study on bionomics of malaria was carried out in Kamlek village, Snuol rubber plantation, Kratie Province where the population had a high prevalence of malaria. Mosquitos were collected monthly between April to September 1998 from 18.00 hr to 6.00 hr by human bait and animal bait. Survey for larva breeding places was also performed. A total of 13 species of Anopheline mosquitos was collected, manly Anopheles philipinensis, An. aconitus, An. annularis, Ain. barbirostris, An. hyrcanus gr, An. jamesii, An. kawari, An. tesselatus, An. umbrosus and An. vagus. They were in various densities with the latter species being the most abundance. Among the vector species. An. maculatus was the most commonly collected with a density of 0.55 per man per night and peak biting was between 20.00 hr and 21.00 hr. The density of An. minimus and An. dirus were 0.11 and 0.74 per man per night with the peak biting time 24.00-01.00 hr and 20.00-21.00 hr respectively. Observation of host preference and feeding habit revealed An. maculatus to be exophagic, anthropophilic and 20 endophilic while An. minimus was both endophilic and exophagic and anthropophilic. An. dirus was endophilic and anthropophilic, these three species were not found positive for malaria infection. However, due to the limited time of survey and an exceptionally low rainfall in the rainy season, an inadequate sample was obtained for analysis. Therefore further investigation is required for at least a year for more information.

Integration of control measures for malaria vectors in endemic areas of Thailand.

Various vector control measures were applied in different endemic areas in two provinces, Saraburi and Chanthaburi, with comparison among different control measures. Application of IGR (insect growth regurator, pyriproxyfen) was introduced at Wat Tam Pra Pothisat, Tab-Kwang District, Saraburi Province. Some integration measures were performed at villages 6 and 8, Patavee, Makham District, Chanthaburi Province. In Tab-Kwang District with low malaria endemicity at the study site predators were not able to be released due to rapid velocity of running water. IGR could effectively control malaria compared to the basin released predators. Another endemic areas villagers 6 and 8, Patavee, Makham, Chanthaburi Province was chosen. Highly endemic multidrug resistant malaria has been prevalent for many years in this area. Integration of Kanda's trapping system, application of IGR, use of both residual spraying and impregnated bed-net methods with etofenprox successfully interrupted malaria infection. The application of these methods as an integrated control system could be adjusted to environmental conditions. The results of this study suggest rapid effective vector control.

A brief survey of phlebotomine sandflies in Thailand.

Sandflies were found in widely scattered localities in Thailand in varied numbers. Daytime resting places for the adults included caves, termite hills, abandoned houses, ancient stone sanctuaries, air-raid shelters, tree hollows, loose bark of dead standing trees and rock crevices. Of fifteen species, P. major major, P. teshi, S. anodontis, S. gemmea, S. hodgsoni hodgsoni, S. perturbans, S. punjabensis and N. vietnamensis were here recorded for the first time in Thailand. P. argentipes and P. major major are interesting in view of their potential as disease vectors.

Observations on the feeding habits of four species of Mansonia (Mansonioides) mosquitoes in Southern Thailand.

Studies on feeding habits of Mansonia annulata, M. annulifera, M. indiana and M. uniformis were carried out in southern Thailand. This study showed that M. annulata and M. uniformis were both strongly exophagic mosquitoes which avoided approaching and entering human dwellings. The biting frequency on the verandah was considerably higher than indoors. M. indiana was not repelled by houses but avoided biting indoors. M. annulifera was endophagic, it was attracted by houses and bit on the verandah as frequently as indoors. Some species showed differential preference for age- and sex-groups of human hosts: M. annulata was more attracted by adolescents and adults than by children and M. annulifera preferred female hosts. The other species did not distinguish between host groups.

Some aspects on biting cycles of Culex quinquefasciatus in Bangkok.

The indoor and outdoor biting cycles of Culex quinquefasciatus were studied in Bangkok. The biting cycle was nocturnally periodic and preferably endophilic in character. There were two minor peaks on top of the nocturnally periodic peak. The first peak was between 2200 and 2300 hours, the latter peak was after midnight being at 0100 and 0400 hours. Parous mosquitoes formed 0%-20.0% of hourly total population. More parous mosquitoes were collected indoor and also during in the latter half of the night. Comparisons made between Bangkok, the none endemic area for Wuchereria bancrofti and Sri Lanka the endemic area, revealed that Bangkok has a lower survival rate of Culex quinquefasciatus, based on parous rates and that the older mosquitoes, which are potentially infective vectors were collected late in the night. This evidence could explain why Bangkok is not endemic area for periodic Wuchereria bancrofti.

DDT-resistant Culex quinquefasciatus: the effect of DDT on the mosquito's size, fecundity and survival.

Resistant strains of Culex quinquefasciatus were selected in the larval stage by exposure to sublethal doses of DDT. The size, body weight and fecundity of DDT-resistant mosquitoes were significantly decreased. There was no significant difference between the longevity of females in the original strain and the DDT selected strains, however, there was a significant difference in the males of the DDT-resistant strains than those of the original strain.

The vectors of Brugia malayi in Southern Thailand.

Mansonia uniformis, with an infective rate of 0.02, was incriminated as the vector of periodic Brugia malayi in Pattani province. Mansonia bonneae and Ma. dives, with infective rates of 0.18 and 0.20 respectively, were the vectors of B. malayi in Narathiwat, where the microfilarial periodicity was the subperiodic form.

Residual effectiveness of insecticidal deposits on various wall surfaces.

The effectiveness of three chemicals DDT, malathion and Dursban was evaluated against larvae and adults of C. p. fatigans. When larvae and adult mosquitoes were tested for susceptibility, they were susceptible to malathion and Dursban. These insecticides were sprayed onto various wall surfaces at a dose of 2 gm per square metre and the residual effect on C. p. fatigans were studied. Dursban residue was superior on all sufaces, giving effective kill for 10-30 weeks, malathion gave satisfactory result on thatch, plywood and galvanized iron while DDT residue failed to produce effective kills.