In filariasis the infectivity of the appropriate mosquito vector is not consistent with the microfilarial density of the host. The reason may be attributed such factors as the time of microfilarial appearance in the peripheral blood of the host, the time of maximum biting activity of the arthropod vector, or the morphological adaptation of the feeding mechanism of the vector.

However, it is quite puzzling to see why the number of microfilariae taken up by mosquitoes is subjected such a great variation, even though the same batch of mosquitoes are fed on the same filarial host under same laboratory conditions. The experiment was designed to observe more detail aspect of this relation.

Adult Aedes togoi (Theobald, 1907) mosquitoes were reared from egg rafes colonized in an insectary. Animals used were Taiwan monkeys, Macaca cyclopsis which had been artificially infected with Wucheria malayi. The animals showed the microfilarial counts as low as nil to ten per slide of 20 cmm³ of blood, which seem to be rather fortunate for this kind of work. The microfilarial density of each animal was counted by taking each ten smears of 20 cmm³ of peripheral blood the ear lobes before and after mosquito bite. Feeding were done in two occations, during 1600-1630 and 1900-1930 hours of the same day. The monkeys were immobilized and a rayon cage, housed 100 female mosquitoes for two days starvation, was exposed to the shaved abdomen of each animal. Fully engorged mosquitoes were transferred to a square rearing cage, which was later placed in the insectary, where kept temperature of 23-27degree C and relative humidity of 80-85 per cent. It was found that filarial larvae of the mosquito body usually develop to the third or infective stage in about 10 days after blood meal under these conditions. Daily dissections were made of these mosquitoes, either living or dead, after one week of rearing. Analysing of the result, the following conclusion was made.

The rate and intensity of infection in mosquitoes are not directly related to the blood counts of microfilariae of the host animals. This is perhaps due to fluctuations of microbial outflow in the peripheral blood of individual animals. The reason of this would be no doubt due to a patch type of microfilarial distribution in the host blood.