NO. I 



BLACK FLIES OF GUATEMALA — DALMAT 



371 



cies. The fluctuations in the larval population of callidutn vary in- 

 versely with those of the adults. When the adult population is at a 

 peak, the larval population is at a low level, and vice versa. Although 

 the pupal trend most nearly coincides with that of the adults, it can be 

 seen that the graph for the adult population is more erratic than that 

 for the pupae. This should be expected since the adult population was 

 relatively small and any variations in meteorological or other environ- 



so 



40 



30 



20 

 10 



.—— ADULTS 

 -.— . — >— LARVAE 

 PUPAE 



JAM. FEBl MAR. APR. MAY. JUM. JUL. AU3. 8EP. OCT. MOV. DtC. 



Fig. 12. — Fluctuation in population of S. (S.) metallicum throughout a year 

 period, expressed as the average number of specimens captured per collection 

 during month periods. (Prepared on 3-cycle semilogarithmic paper.) 



mental conditions might very well bring about temporary absence of 

 biting adults, which would be magnified on the graph. On the other 

 hand, the pupal population would not be similarly affected by tempo- 

 rary changes in environmental conditions. 



With our present knowledge of the seasonal variation in population 

 of the three principal anthropophilic species, it would be necessary to 

 develop a larval control program in the onchocerciasis region based on 

 the following information. If only 6". ochraceum, the principal an- 

 thropophilic species, is to be controlled, streams must definitely be 

 treated during April and October, as well as somewhat before and 



