48 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I25 



Ornithodorus turicata did ingest microfilariae in significant numbers, 

 it was not demonstrated whether or not it could support development 

 to advanced stages. 



In searching for an appropriate vector, one would naturally choose 

 for study those arthropods that can be suspected by virtue of the 

 coincidence of their distribution with that of the disease, and those 

 that experimentally will ingest microfilariae. In Guatemala, Culicoides 

 spp. and SimuUum spp. appear most likely. However, Culicoides are 

 most prevalent in the onchocerciasis zone during the rainy season when 

 human exposure to their bites is at a minimum. Also, they are more 

 active in the shade, somewhat reducing their opportunity for frequent 

 blood meals on the field workers. In the cases of natural infection of 

 Culicoides reported above, the species to which the filariid larvae be- 

 longed were not carefully determined. The experimental findings of 

 Gibson and Ascoli clearly demonstrated that microfilariae of O. 

 volvulus, although ingested, did not develop further in Culicoides spp. 

 For these reasons it is believed that Culicoides can be eliminated as a 

 possible vector of onchocerciasis. 



The aforementioned investigations of Blacklock, Strong, Hoffmann, 

 Vargas, De Leon, Wanson, Henrard and Peel, Gibson, and Dalmat 

 indicate that Simulium species transmit onchocerciasis. The failure 

 of microfilariae to develop in arthropods other than Simulium spp., the 

 finding of black flies naturally infected with larvae of O. volvulus, 

 the successful infection of these flies with subsequent development of 

 the microfilariae, plus epidemiological evidence concerning the distri- 

 bution of the anthropophilic species in Guatemala, quite definitely in- 

 criminate the Simuliidae as the vectors of the disease. 



PREDATORS OF THE SIMULIIDAE 



To help determine the relationship of animal life to the incidence 

 of Simulium in the onchocerciasis zone, and in an attempt to ascertain 

 if there are other reservoirs of Onchocerca volvulus besides man, a 

 survey was made of both the aquatic and terrestrial fauna in the region 

 of San Pedro Yepocapa. The taxonomic list of those species collected 

 is given in Appendix II. 



Only certain of the insects, fishes, and birds played any role in the 

 reduction of the black-fly population. The larvae of dobson-flies 

 {Corydalus sp.) and caddiceflies (Smicridea, or near), the naiads and 

 adults of dragonflies {Lihellula sp.) and damselflies {H etaerina sp.), 

 and the nymphs and adults of the giant water bug {Ahedus ovatus) 

 were found to feed on the larval and adult black flies. Investigators 

 have reported finding some of these insects feeding on black-fly larvae 



