Studies on the flight range and dispersal of Simulium damnosum (Diptera: Simuliidae) in the rain-forest of Cameroon.

Five marking/recapture experiments were carried out on Simulium damnosum in the rain-forest of the United Republic of Cameroon, in order to determine the regression in biting density at increasing distances from the marking point. Flies were captured unfed, marked with fluorescent dust, and then released on the bank of a large river. Recaptures were made over the six-seven days after marking, at seven stations situated from 200 m to 79 km along a large river, from the marking site. Marked flies, which showed fluorescent pigment when examined under an ultraviolet lamp, were recovered at all seven sites. The ratios of the number of recaptures per man-hour at each distant site to the recaptures per man-hour at the marking point were calculated to obtain values for the proportional biting density (Z). The value of Z declined in a logarithmic manner with increasing distance from the marking site, such that it fell to 0-1 at distances of 34-1 km on a large river, 5-5 km on a small river, and 1-5 km on a road leading away from a large river. The peak number of flies recaptured at the farthest sites along a large river (56 km and 79 km) occurred one day later than at the station nearest the marking point. The dispersal of marked flies which had fed on volunteers carrying Onchocerca volvulus microfilariae, was studied along a large river. Of three flies recaptured 24 km upstream from the marking point, one contained 10 infective larvae of O. volvulus.