NO. I BLACK FLIES OF GUATEMALA — DALMAT 343 



place was recorded. These data included: (i) Date of collection; 

 (2) name of river, finca, municipality, department, etc.; (3) width 

 of stream ; (4) depth of stream ; (5) temperature of water ; (6) speed 

 of current ; (7) altitude of region ; (8) pH of water ; (9) if the stream 

 is open to the sun or covered by vegetation; (10) description of the 

 stream bed — muddy, sandy, rocky, quantity and type of plants pres- 

 ent ; ( II ) depth at which eggs, larvae, and pupae are found ; ( 12) sub- 

 stratum of the various stages collected — small or large stones, rocks, 

 sand, mud, branches, twigs, roots, narrow or wide leaves, etc. ; and 

 (13) if the larvae or pupae are found in parts of the stream that have 

 a normal grade, or ones with cascades or waterfalls. To secure these 

 data, each collecting group carried with it the necessary equipment 

 which included an altimeter, extensible rule, corks for floating on sur- 

 face of water in calculating current speeds, chronometer, pH meter, 

 thermometer, and a vasculum for carrying plant samples. 



The data were transferred to the books in which all collections were 

 chronologically accessioned, along with the identifications of the indi- 

 vidual specimens. They were subsequently digested according to 

 species so that statistical information could be derived from them. The 

 following paragraphs summarize the findings. 



ALTITUDE PREFERENCES 



Table 23 presents in condensed form the data concerning the alti- 

 tudes of those parts of streams in which the Guatemalan black flies 

 were found to breed (see also Appendix III, table 36). It will be 

 noticed that the truly coastal species are few in number — Simulium 

 earlei, exiguum, pulverulenfum, and samboni. Of the four species, 

 exigumn and pulverulentum do attack man, but because of their abun- 

 dance primarily in low regions, where onchocerciasis is not wide- 

 spread, their over-all importance in the transmission of the disease 

 could not be very great. Of course, they may serve as the only vectors 

 in certain areas where they exist to the complete exclusion of ochra- 

 ceunt, metallicum, or callidum. On the other hand, the number of 

 species preferring high altitudes (above 6,000 feet) is great. It in- 

 cludes Gigantodax aquamarensis and wrighti; Simulium aureum, 

 burchi, carolinae, delatorrei, ethelae, kompi, microbranchium, and 

 tricornis; Cnephia pacheco-lunai and roblesi. Of these, S. aureum, 

 C. pacheco-lunai, and C. roblesi are found almost entirely over 7,000 

 feet above sea level. None of these high-altitude breeders is anthro- 

 pophilic. 



The vast majority of species live within the altitude range from 

 2,000 to 6,000 feet above sea level. The principal anthropophilic spe- 



