NO. I BLACK FLIES OF GUATEMALA — DALMAT 337 



tion would probably prevent insecticides from filtering to the resting 

 places at lower levels. 



Colonisation of Black Flies 



At the inception of the work in this laboratory, one of the important 

 aims was the establishment of a self-perpetuating colony of anthropo- 

 philic black flies. It was hoped that such a colony would supply 

 "clean," or uninfected, flies for use in the study of the developmental 

 stages of Onchocerca volvulus. This project, undertaken at the field 

 laboratory in San Pedro Yepocapa, was continued during a 3^-year 

 period. Although the successful establishment of a colony was not 

 achieved, the techniques and some of the results are interesting, and 

 may prove of some value for future experimentation. 



Using practically any method, eggs could be reared through to 

 adults without much difficulty. Previous workers in Guatemala had 

 simulated a cascade by arranging a series of inclined pans in such a 

 manner that the water dropped from one into another. The pans were 

 stocked with larvae which readily pupated, the adults emerging in 3 

 to 5 days. This system had a number of drawbacks, the principal ones 

 being: (i) that emerging adults were not confined for further use, 

 (2) the cocoons did not appear normal, being rather translucent and 

 exceedingly soft, and (3) the young larvae could not easily be confined 

 in the pans. 



To rear adults from pupae for taxonomic studies (see section on 

 "Taxonomy of the Guatemalan Simuliidae" ) , we used lengths of glass 

 tubes, both ends of which were stoppered with slightly moistened 

 cotton. This technique yielded successful results, especially when the 

 holding tubes used were large enough to permit the adults sufficient 

 room for movement without having to press against the moist glass. 

 Adults reared in this manner emerged in perfect condition and, there- 

 fore, could be employed in the colonization studies. Another device 

 employed in our work was an "incubator-aerator," first described by 

 Thomas (1946). It consisted of a series of baffles, arranged in de- 

 scending order to form a riffle board, over which a constant source of 

 water flowed (pi. 20, fig. i). The structure was enclosed in canvas 

 which was constantly being moistened. The evaporation of the water 

 on the canvas sides of the apparatus served as a method for cooling 

 the interior. Extending from the wood frame at one end are a series 

 of vials, the mouths of which pass through an opening in the board. 

 Emerging flies, attracted to the light source near the vials, enter them 

 and can then easily be collected. 



One other artifact was constructed at the laboratory for use in rear- 



