NO. I BLACK FLIES OF GUATEMALA — DALMAT 309 



PRINCIPAL ANTHROPOPHILIC SPECIES 



SIMULIUM (5.) OCHRACEUM WALKER 



It has been particularly difficult to study the life history of this spe- 

 cies because of its characteristic habitat and mode of oviposition. It 

 is found breeding principally in infant and young streams which flow 

 through "rugged" terrain. These streams are usually concealed by a 

 dense canopy composed of three to four layers of vegetation — emer- 

 gent vegetation, overgrowth of grasses and other plants preferring a 

 moist environment, shrubs and low trees, and finally, tall trees. Thus 

 the breeding places are difficult to find and somewhat inaccessible. 

 The species has been collected at altitudes ranging from 500 to 6,000 

 feet, with one collection at 8,200 feet, but most commonly from 3,000 

 to 5,000 feet. At the breeding areas the streams show the following 

 characteristics (Appendix III, table 31) : 



Width: Range, i in. to 15 ft. ; optimum, i ft. to 5 ft. 



Depth : Range, i in. to 3 ft. ; optimum, i in. to 5 in. 



Temperature: Range, 10° C. to 22° C. ; optimum, 18° C. to 20° C. 



Current : Range, i in. per second to 40 in. per second ; optimum, i in. per second 



to 10 in. per second. 

 pH : Range, <6.o to 8.0; optimum, 7.1 to 7.5. 



Eggs, larvae, and pupae have been found on parts of the following 

 plants that were floating on the surface of the streams or were emer- 

 gent from them : 



Axonopiis compressus (Sw.) Beauv. Ipomoea sp. 



Tradescantia commelinoides R. and S. Hyptis sinuata Pohl 



Tripogandra cumanensis (Kunth) Woodson 



The immature stages have occasionally been found on debris vege- 

 tation, but never on hirsute plants. The following species of black 

 flies are those most commonly found breeding (in order of frequency) 

 in the same streams with 5". ochraceum (Appendix III, table 33) : 



S. metallicum S. mexicanum S. capricornis 



S. callidiim S. jobbinsi S. acatenangoensis 



S. rubicutidulum S. smarti S. parrai 



S. doimisi S. veracnisanum 



The adults mate soon after emergence, the spermatozoa being stored 

 in the spermatheca. Development of the eggs to larvae depends on 

 the ability of the female to secure blood meals before she oviposits. 

 The time required for eggs to develop within the female is not known. 

 Fertilization takes place from the spermatheca as the eggs are laid. 

 S. ochraceum, unlike the other two species considered here, oviposits 



