Blood meal enhanced onchocerca development and its correlation with fecundity in laboratory reared blackflies (Diptera, Simuliidae).

Simulium ornatum s.l. is a natural vector of Onchocerca lienalis in Britain. These studies investigated the role of the blood meal on the development of the parasite in the thoracic musculature. Infection was by the standard technique of intrathoracic injection, allowing precise doses of microfilariae to be administered. Prior to infection flies were fed on bovine blood through a chick skin membrane. In 3 trials the number of O. lienalis larvae developing in non-blood fed flies was between 60.2 and 68.4% lower than in blood fed insects. The mean number of eggs recovered per fly ranged from 131.7 to 187.5 in infected groups. In uninfected control groups the levels ranged from 315.4 to 378.1 per fly. This represents reductions in fecundity of between 50.4 and 51.7% in infected groups of simuliids. It appears that in order to maintain relatively high levels of transmission an intermediate blood meal, between uptake of microfilariae and release of infective stage larvae, may be important. Furthermore, great care must be taken when using fecundity to assess the age of simuliids. Levels of parasitic infection may affect egg production to a much greater extent.