NO. I BLACK FLIES OF GUATEMALA — DALMAT 47 



It is true that the distribution of ochraceum more nearly coincides 

 with that of the disease than does the distribution of metallicum or 

 callidum. S. ochraceum, although found breeding in areas 500 to 

 6,000 feet in altitude inside and outside of the disease zone, is much 

 more abundant in the infected regions, 3,000 to 5,000 feet. On the 

 other hand, 5'. metallicum is just as numerous inside the disease zone 

 as it is on the outside, and it is found in a far greater range of altitude. 

 Both species will ingest microfilariae in equal numbers. 



Investigators, up to the present time, have been attempting to trace 

 Onchocerca development in various bloodsucking arthropods other 

 than simuliids but have met with little success. Since some species of 

 Culicoides are voracious feeders on man, attacking all parts of the body, 

 biting actively inside and outside of buildings, and since they are 

 known to serve as the intermediate host of certain other filariid worms 

 of both man and animals, they have been the subject of a good deal 

 of study in regard to their possible role in the transmission of oncho- 

 cerciasis. Dampf (i936a,b), in Chiapas, Mexico, found developmental 

 forms of filariid larvae in 3 of 107 wild-caught Culicoides jilariferus 

 which he dissected. Dampf stated that some of these forms correspond 

 in size to O. volvulus and others to O. cervicalis. De Leon (Pan 

 American Sanitary Bureau, 1945), in Guatemala, found the "sausage" 

 form of a filariid worm in the thoracic muscles of a wild-caught Culi- 

 coides. Gibson and Ascoli (1952) collected numerous examples of five 

 species of Culicoides from infected individuals in the Yepocapa region. 

 Although two species ingested microfilariae, none of them supported 

 development of the larvae. They found no natural infection in flies of 

 this genus, and concluded that at least the species of Culicoides with 

 which they worked did not transmit onchocerciasis. Strong et al. 

 (1934) found that Aedomyia squamipennis, prevalent in the part of 

 the Guatemalan onchocerciasis zone where they were working, did 

 not ingest microfilariae from infected patients, while more than 50 

 percent of the Simulium flies fed on the same patients did take up 

 microfilariae. Strong stated that the mosquito probably does not take 

 up microfilariae because of its long proboscis, which penetrates deeply 

 while sucking blood, with a minimum of laceration or abrasion. He 

 also believes that the saliva of the mosquito might repel microfilariae. 

 De Leon (1941) found "sausage" forms, which he considered to be 

 0. volvulus, in dissections of fleas collected from onchocercotic pa- 

 tients. Vargas (1941), in Mexico, fed the following arthropods on 

 infected subjects : Pulex irritans, Ctenocephalides canis, Cimex lectu- 

 larius, Triatoma picturata, Pediculus humanus, Aedes aegypti, 

 Anopheles psetidopunctipennis, and Ornithodorus turicata. Although 



