NO. I BLACK FLIES OF GUATEMALA — ^DALMAT 49 



in such numbers that they concluded that they play an important role 

 in reducing the black-fly population. However, the observations made 

 in the Guatemalan streams indicate that they have very little, if any, 

 practical effect. The adults of the fossorial wasp, Oxyhelus pyrnrus, 

 were the most obvious predators of adult black flies. When collecting 

 black flies from human subjects, these wasps would hover nearby, 

 grabbing the flies as they began to feed. The wasps themselves are 

 often numerous enough to constitute a pest. Since simuliids are only 

 one of several groups of flies that serve as prey for these wasps, it is 

 doubtful whether the number of black flies consumed would signifi- 

 cantly reduce the total population. 



Although representatives of 7 of the 25 species of birds collected 

 contained remains of adult simuliids in their stomachs, the number 

 of flies ingested was actually small. In the case of several of these 

 birds, the ingestion of black flies must have been accidental, since 

 insects do not form a normal constituent of their diet. 



The fish Profundulus punctatus Giinther has been found to be the 

 most efficient predator of Simulium. Examination of over 200 of 

 these minnows yielded numerous larvae in all but 10, these being fry 

 too small to feed on insects as large as the black flies. In addition, 

 the contents of the digestive tract of 12 of these fish contained parts 

 of adult flies, indicating that the fish also devour the simuliids as the 

 latter are emerging from the pupal case or while they are ovipositing. 

 It should be noted that the more typical breeding places of Simulium 

 ochraceum, the species believed to play the major role in the transmis- 

 sion of onchocerciasis in Guatemala, are too shallow and small to sup- 

 port development of Profundulus punctatus, the predatory minnow. 

 Undoubtedly this minnow must reduce the black-fly population in the 

 streams where it exists, but owing to the enormous breeding potential 

 of the flies and the constant reduction of the fish by the Indians who 

 use them as food, the actual effect on the over-all fly population must 

 be small. However, in restricted areas which can be kept under super- 

 vision, this fish may be useful as a possible agent for biological control. 



PARASITISM OF THE SIMULIIDAE 



Mention should be made of a few other forms found associated with 

 Guatemalan Simuliidae that probably affect their normal development. 

 On numerous occasions comparatively large nematode larvae of the 

 family Mermithidae have been found coiled in the abdomen of Si- 

 mulium larvae. At times two or three were taken from one black-fly 

 larva which did not seem to be particularly hampered by them. Since 

 the same have been noted in the adults of 6'. metallicum and S. ochra- 



