1981 Volume 9 Issue 3-4 Pages 187-197
Females of Simulium ochraceum which were fed on a carrier of the Guatemalan strain of Onchocerca volvulus microfilariae were maintained under natural conditions at five different altitudes (350-1, 500 m) within and outside of the onchocerciasis endemic zone. The results suggested the probability that these insects' chance of surviving increases with altitude. The infective stage of O. volvulus larvae was reached on the eighth day at Maria Santisim a (alt. 650 m). At higher altitudes (1, 200-1, 500 m), however, no larval development beyond the late first stage occurred, except in one S. ochraceum female (at Guatemala City, 1, 500 m) which yielded late second-stage worms on day 16. The length of the gonotrophic cycle was three or four days irrespective of altitude. Heat accumulation, calculated by means of a self-registered thermometer, suggested that the predicted period required for larvae to reach the infective stage in the vector varies considerably with altitude (4.4-28 days). The relationship between the rate of development of O. volvulus larvae at varying altitudes, and ambient heat accumulation, is also discussed.
