332 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I25 



highest proportion of infected flies were chosen as subjects for the 

 flight-range and longevity study. 



Since it was desired to determine how long infected adults can live 

 in nature, as well as how far they are able to fly, in comparison with 

 noninfected flies, it was decided to postpone the recapture of stained 

 flies until several days after staining was begun. Had captures been 

 initiated concurrently with release of the flies, the population of 

 stained flies probably would have been unnecessarily reduced. A total 

 of 669 visits was made on 60 nonconsecutive days to the 21 collecting 

 stations that had been established in all directions and at varying dis- 

 tances from the release point. Collected flies were examined under 

 the dissecting microscope as they were introduced singly into an 

 alcohol-glycerine-chloroform solvent. Flies found to be stained were 

 then identified as to species, fixed, embedded, serially sectioned in the 

 sagittal plane, and prepared as stained mounts. These were examined 

 microscopically to determine if the flies were infected and the degree 

 of development reached by the ingested filarid larvae. 



Altogether, 40,474 simuliid flies, which had fed on onchocercotic 

 patients, were released after being marked with the aniline dyes. Dur- 

 ing a 2-month period subsequent to the release of these flies, 144,708 

 simuliids were captured at the 21 collecting stations, of which 55,366 

 were S. ochraceum, 81,475 metallicum, and 7,867 callidum. Among 

 these were 42 flies that had been stained by one of the aniline dye 

 markers. Sectioning of these 42 marked flies revealed only three in- 

 fections. A study of the developmental stages left no doubt that 

 the flies became infected on the day they were marked and released. 

 One of the infected flies {S. ochraceum) had flown 2.9 miles from the 

 release point in 2 or 3 days; the other two (one ochraceum and one 

 callidum) had flown 2.y miles in 3 or 4 days. Of the flies that were 

 not infected, some had flown as far as 9.6 miles. 



Although only a small number of infected flies were recovered, it 

 can be concluded that infected black flies can, and do, travel some 

 distance from the point of infection. From past experience with nu- 

 merous infection experiments (Gibson, 1951a), it is known that ap- 

 proximately one-half of the flies that take blood meals from a heavily 

 infected person ingest microfilariae and subsequently become infected. 

 On this basis it can be presumed that approximately one-half of the 

 40,474 flies that were fed, stained, and released in the present study 

 became infected. If no mortality occurred, it would therefore be ex- 

 pected that infections should be found in one-half of the 42 flies that 

 were recovered. Since only three infected flies were recovered, the 

 possibility is* suggested that infection with Onchocerca volvulus may 



