NO. I BLACK FLIES OF GUATEMALA — DALMAT 57 



However, they generally prefer rapidly flowing, shallow, clear, cool 

 water where they can attach to vegetation or stones. 



Different species of Simuliidae show a definite predilection for cer- 

 tain stream characteristics. It can be said that the morphological "age" 

 of a stream (i.e., its size, form, current flow, bed, and vegetation) at a 

 particular section will, to a large degree, determine which species of 

 Simuliidae will breed there. The principal anthropophilic species, 

 considered to be the vectors of onchocerciasis, prefer "infant" or 

 "young" sections where the stream is narrow, having a comparatively 

 low volume of water, and where the bed is earthen to arenaceous, with 

 an abundance of cover and emergent vegetation to serve as anchorage 

 for larvae and pupae, and as shade for the breeding haunts. Tomas, 

 or man-made waterways, resemble young streams in their morpho- 

 logical characteristics and are often a source of prolific breeding of 

 the anthropophilic species, especially Simidium metallicum. The zoo- 

 philic species prefer "adolescent" to "mature" streams with a large 

 volume of water, the stream bed composed of gravel, stones, and rocks 

 for anchorage of the immature stages, and with a paucity of emergent 

 and cover vegetation. Certain species choose waterfalls as their pre- 

 ferred breeding ground. 



The streams of the Yepocapa region are all formed from under- 

 ground springs or seepages which leave the ground at a point where 

 the natural curvature of the land intersects a water table and where 

 the earth is sufficiently porous. 



Relative to chemical control of Siniulium larvae in the Yepocapa 

 region, accurate determination of stream volumes can best be made at 

 the mouths, where they join with other streams. 



ENTOMOLOGICAL STUDIES IN GUATEMALA 



Since Dr. Robles' discovery of the presence of onchocerciasis in 

 Guatemala in 191 5, and since the confirmation by Blacklock in 1926 

 of Robles' hypothesis of transmission by Simulium species, com- 

 paratively few entomological investigations of these flies have been 

 made in Guatemala. In 1931 and again in 1932 Harvard University 

 sent an expedition to Guatemala, headed by Dr. Richard P. Strong, 

 for the purpose of investigating all phases of onchocerciasis. Dr. 

 Joseph C. Bequaert (1934), who was in charge of the entomological 

 investigations, reported that up to the time of his studies he was able 

 to find published records of only three Guatemalan Simuliidae, Simu- 

 lium metallicum Bellardi, 6^. mexicanum Bellardi, and 6". exiguum 

 Roubaud. During the course of his work he discovered three more 

 species, 6'. ochraceum Walker, S. callidum (Dyar and Shannon), and 



