Abstract
1. The behaviour and development of Brugia patei has been followed in the mosquito host, Mansonia uniformis, from ingestion of the microfilariae to the development of the infective stages.2. The microfilariae penetrated very rapidly out of the stomach into the abdomen of the mosquito; 80% of them escape from the stomach during the first 50 minutes after a blood meal.3. The microfilariae migrate from the abdomen to the thorax through fat body cells and the heart during the first 140 minutes followed engorgement and begin to penetrate the indirect flight muscles within 15 minutes from engorgement. During this migration microfilariae were found in close association, suggesting that they follow similar pathways of migration through the body of the mosquito.4. Most microfilariae (98%) have settled in the indirect flight muscles within 2 hours of engorgement. In these muscles the larvae digest away the muscle surrounding them but do not begin to elongate until the third or fourth day after the blood meal. The rate of development varies from one mosquito host to another, but about 80% of the larvae have developed to the infective stage by the ninth to tenth days after the infective feed. The infective stages concentrate in the head and proboscis of the mosquito vector. The development of B. patei is faster than that of B. pahangi in mosquitoes from the same colony.5. The efficiency of M. uniformis as a vector of B. patei is compared with the similar efficiency of M. longipalpis as a vector of B. malayi. In both mosquitoes the majority of the microfilariae ingested develop to the infective stage. M. uniforms is also an efficient vector of B. pahangi.6. The development of the parasite is discussed briefly with reference to knowledge of the physiological events within the mosquito host subsequent to the blood meal.