366 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 25 



be very slight, it is unlikely that it affects the normal development of 

 the Simuliidae. A comparison of the dissolved oxygen in the moun- 

 tain streams of the Yepocapa region with that of the streams in the 

 coastal region or other sections of the country might show a relation- 

 ship between oxygen content and the ability of the various species to 

 breed. Such a study was not carried out because of the impracticability 

 of doing the oxygen determinations under field conditions in most 

 parts of Guatemala. 



RELATION OF DISSOLVED SALT TO BREEDING OF BLACK FLIES 



The same 62 streams that were used for dissolved-oxygen determi- 

 nations, were also tested for salt content. A simple salimeter was 

 employed from which readings could be made directly according to 

 its displacement of water. Since no streams in the Yepocapa region 

 exhibited salt content, the study of this factor was discontinued. 



EFFECT OF FOREIGN SUBSTANCES IN STREAMS ON 

 BREEDING OF BLACK FLIES 



In general, it has been observed that no species of Simuliidae will 

 breed in streams that have been polluted by large quantities of agricul- 

 tural or chemical wastes. This was particularly noticeable in the 

 Rio Guacalate at Pastores, Sacatepequez, where Simulium exiguum 

 normally breeds in great abundance. During the months of the corn 

 and coffee harvests, large quantities of waste cane and leaves and coffee 

 pulp are dumped into the stream. Within a few days the larvae and 

 pupae of 6". exiguum disappeared from the stream and did not return 

 until the rainy season once again cleared the debris and permitted more 

 normal oxygenation. The streams of Guatemala are commonly used 

 by the rural population for washing clothes. The large amount of 

 soap that is introduced into the streams does not seem to affect the 

 breeding of the Simuliidae except in the immediate vicinity of its 

 release. Wherever sewage or garbage is discharged into streams, no 

 black-fly breeding will be found for long distances downstream. 



ECOLOGICAL NOTES 



The following ecological notes refer to species which were not dis- 

 cussed in the first seven parts of the subsection entitled "Immature 

 Stages" or included in tables 23 through 30. 



Simulium (Byssodon) benjamini Dalmat. — This species has been 

 found in only two streams, Rio Sokcha, Poctun, Peten, and a stream 

 (name not known) in Coban, Alta Verapaz, both being part of the 



