NO. I BLACK FLIES OF GUATEMALA — DALMAT 35 



of certain preferred aquatic or semiaquatic plants. We have rarely 

 found eggs, larvae, or pupae on hirsute vegetation. It was also noticed 

 that two particular semiaquatic plants, Renealmia aromatica and R. 

 strobilifera, were very commonly used by the female flies as the sub- 

 stratum on which to deposit eggs. Perhaps, then, the larvae and pupae 

 of the important biters of human beings also showed preference for 

 certain plants as anchorage. 



The vegetation, which plays such an important part in the ecology 

 of Simulium larvae and to a large extent controls the breeding of the 

 anthropophilic species, can be divided into four categories : ( i ) Border 

 vegetation, (2) emergent vegetation, (3) debris, and (4) mosses and 

 algae. 



(i) The border vegetation includes those trees and shrubs along 

 the margin of streams that offer shade to the breeding places, and the 

 falling leaves and stems of which also produce debris that will be used 

 for anchorage by the immature stages of black flies. 



(2) The emergent vegetation encompasses all those plants that grow 

 from the stream bed and banks, parts of which enter the water. These 

 include the roots, vines, and trailing leaves of marginal plants, as well 

 as truly aquatic vegetation. Upon this emergent vegetation are found 

 the eggs, larvae, and pupae of the anthropophilic species. 



(3) The debris of a stream is comprised of all floating parts broken 

 loose from plants, and refuse and artifacts that are transported by the 

 stream. The debris usually accumulates in certain spots where it may 

 produce a small dam. The leaves and stalks of bananas, corn, and 

 sugarcane, as well as decomposing members of various other trees and 

 shrubs, all serve as excellent substrata for immature stages of both 

 anthropophilic and zoophilic species. 



(4) The mosses and algae may form dense mats over the walls of 

 the stream, on the rocks and emergent vegetation, and in the water 

 itself. These usually grow in the less turbulent parts of a stream and 

 generally inhibit Simulium breeding. However, in several streams in 

 the Yepocapa onchocerciasis zone Simulium, larvae were found at- 

 tached to the moss Thuidimn dclicatidum (Hedw.) Mitt., and were 

 apparently thriving. 



If the different species of Simtdimn showed definite preferences for 

 particular vegetation associated with their breeding places, it was felt 

 that a study to determine the species and characteristics of the aquatic 

 and semiaquatic plants in the streams within the onchocerciasis zone 

 and outside of it might, in part, explain the circumscribed distribution 

 of the disease. Also, in considering the establishment of a sound 

 Simulium control program, the resting places of the adult flies should 



