[Effect of a sublethal dose of an insect growth regulator on the physiology of onchocercosis vectors].

In most of the large scale vector control programs, the larviciding operations are not fully successful, resulting in a surviving vector population due to the use of sublethal doses. This problem leads the authors to study the effect of such doses upon the future of the residual population in order to know if it represents an epidemiologically dangerous population. One insect growth regulator was selected to study this phenomenon using Onchocerca volvulus as the parasite and Simulium damnosum s.l. as the vector. The experiment was conducted under field conditions by treating a river of a savanna area in north Cameroon where onchocerciasis remains endemic. The sublethal doses yielding 20% in adult blackflies from treated larvae was determined and the effects on physiological and vectorial capacities were assessed. The authors also carried out observations on the peritrophic membrane formation and the passage of microfilariae into the hemocele. The observation of flies fed on Onchocerca after larval treatment showed that this insecticide had a light effect on female longevity but did not induce any modifications in the life cycle of the parasite. An unusual high proportion of infected females, observed by the authors, is probably due to an anomaly in the phenomenon of limitation. However, the histological analysis showed to the evidence that no apparent difference between treated and untreated blackflies was observed although the process of blood meal digestion seemed slightly altered in treated flies.