NO. I BLACK FLIES OF GUATEMALA — DALMAT 333 



have a deleterious effect upon the flies and thereby cause the early 

 death of many of them. It has been repeatedly observed in the labora- 

 tory that simuliids infected wtih O. volvulus larvae show a high mor- 

 tality rate during the first 4 days after the infective meal ; furthermore, 

 they die more rapidly than uninfected flies under laboratory conditions. 

 Thus, because so few infected flies were recovered in the present ex- 

 periment, none of which had survived more than 4 days after infec- 

 tion, it is probable that the high postinfection mortality observed in 

 the laboratory also occurs in the field. 



Lebied (1950), in his studies of the development of Onchocerca 

 volvulus in Simulinm damnosiim, concludes that pathological changes 

 caused by "sausage" forms developing in the fibers of the indirect 

 flight muscles presumably restrict the flght range of infected flies, 

 thereby limiting the spread of onchocerciasis. 



In summarizing the findings on flight range and longevity of both 

 noninfected and infected flies, the following observations can be made : 



Uninfected flies are capable of flying (without the aid of prevailing 

 winds) at least 9.7 miles, measured as a straight-line distance. If the 

 extremely irregular nature of the terrain were to be taken into account, 

 this flight capacity should undoubtedly be increased. 



The longevity of uninfected flies, calculated from the time of release 

 to recapture, is from 3 to 85 days. This represents only an estimate of 

 the natural longevity, since it is impossible to determine how long 

 these wild flies had been living prior to being stained, or how long 

 they would have survived after the recapture date had they been 

 free in nature. 



Thus it has been shown that the females of the principal anthropo- 

 philic species of Guatemalan Simuliidae have a high potential for 

 survival and for traversing relatively great distances under normal 

 conditions. Therefore, in any control program aimed at the reduction 

 of anthropophilic species, whether infected or not, relatively large 

 areas would have to be included to minimize infiltration of flies from 

 outside of the treated region. 



Since infection with Onchocerca volvulus does reduce the flight 

 capacity and longevity of the flies, a program directed solely against 

 infected flies, with a view toward preventing their migration to neigh- 

 boring noninfected regions, would not have to be as extensive. From 

 the limited data obtained in the studies of the flight range and longev- 

 ity of infected flies, it can be seen that these flies can travel at least 

 2.9 miles in 2 or 3 days. Therefore, measures for the control of in- 

 fected Simulium would have to be extended at least 2.9 miles beyond 

 the area to be protected. In any program for the control of human 



