Abstract
1. Tests were conducted to determine susceptibility of eight species of mosquitoes to infection with microfilariae of Dirofilaria immitis. Highest infection rates and largest numbers of infective larvae were found in specimens of Aedes togoi fed on an infected dog and examined 12 days thereafter. Other species tested were Culex pipiens fatigans, Culex pipiens pallens, Culex tritaeniorhynchus, Aedes albopictus, Aedes aegypti, Armigeres subalbatus, and Anopheles sinensis. 2. There were no outstanding differences in D. immitis infection rates among Aedes togoi of four age groups allowed to feed on an infected dog. 3. Microfilariae in peripheral blood of a dog under treatment for dirofilariasis during a 21 day period remained infective for mosquitoes, Aedes togoi, fed on the dog on 10 days during the course of treatment. Decline in numbers of microfilariae in blood of the dog was much more rapid than decline in numbers of infective immitis larvae in mosquitoes which had been fed on the dog and dissected 12 days thereafter. 4. In surveys of microfilaremia among dogs at Kochi, Shikoku the factors which showed most striking correlation with high incidence of infection with D. immitis were age and habitat. Dogs from wooded foothills outside Kochi City proper showed a much higher microfilaremia rate than those from urban Kochi and from a seaside area near the city. Short haired dogs showed an infection rate nearly twice that of long haired animals, and males were infected nearly twice as frequently as females. 5. Only eight of 1, 813 adult female mosquitoes of seven species obtained in light traps, and in resting and biting collections in the vicinity of dog kennels at the seaside, urban Kochi, and wooded suburban foothills 7, 000-10, 000 meters from urban Kochi were infected with larvae of Dirofilaria immitis. Five of these were specimens of Culex fatigans, the remaining three were examples of Aedes togoi. Four of the infected C. fatigans were collected at the seaside area, and one was found in urban Kochi. The three infected specimens of Aedes togoi were found in the wooded foothills, the only area where this mosquito was most numerous.
