Identification of species-specific DNA sequences in North American blackflies.

Blackflies are vectors for Onchocerca volvulus, a filarial parasite that infects tens of millions of people in Africa and Latin America. Different species of the insect vectors, varying greatly in their ability to transmit the infection, may populate overlapping geographical regions and be morphologically similar. A rapid and reliable method for distinguishing among blackfly species is presently not available. We have isolated cloned DNAs coding for repetitive sequences that can distinguish between two species of North American blackflies, Simulium pictipes and Simulium vittatum. These DNAs do not cross hybridize to three African blackfly species. The assay is very sensitive, less than 1/1000th of the amount of DNA in a single fly being sufficient for detection with a radioactive probe. Diagnosis with nonradioactive probes by a procedure that is amenable for use in the field was also demonstrated.