NO. I BLACK FLIES OF GUATEMALA — DALMAT 379 



origin. Skin biopsies of 884 local animals (mainly horses and cattle) 

 in the Yepocapa area showed that 12 percent of the horses and cattle 

 were infected with skin-inhabiting microfilariae superficially similar 

 to those of human onchocerciasis (Gibson, 1951a). Since ochraceum 

 is definitely anthropophilic in its feeding habits, its natural infection 

 is more likely to be exclusively of human origin. Also, since the more 

 extended, noninterrupted blood meals of ochraceum permit it to ingest 

 numerous microfilariae, which, in turn, cause the death of large num- 

 bers of the flies, fewer infected flies of this species can be found than 

 of metallicum, which feeds more nervously and for a shorter time 

 interval. 



It should be understood that the author does not believe that S. 

 ochraceum is the only vector of onchocerciasis in Guatemala, but 

 rather that it is the most efficient and important one. It is likely that 

 S. metallicum is a good secondary vector and that callidum also trans- 

 mits the disease, although to no significant degree. Probably in parts 

 of the onchocerciasis zones where the ochraceum population is low 

 but where haematopotum, veracruzanum, or exiguum are abundant, 

 these species may be important in transmission (Gibson and Dalmat, 

 1952). In considering programs for the control of onchocerciasis, 

 although prime attention should be given to the eradication of .S. 

 ochraceum, control of metallicum is also indicated. Small-scale con- 

 trol studies, based on our knowledge of the life history, optimum 

 breeding conditions, and habits of the immature and adult forms, have 

 already been conducted in the Yepocapa region. It is hoped that the 

 Guatemalan federal health authorities, in cooperation with the local 

 plantation owners, will continue with control activities on a large 

 scale, using our experiences and indications as a groundwork. 



LITERATURE CITED 



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1936. Standard methods for the examination of water and sewage. 8th ed., 

 309 pp. New York. 

 Bellardi, L. 



1859. Saggio di Ditterologia Messicana, vol. i, pp. 13-14. Torino. 

 1862. Saggio di Ditterologia Messicana, vol. 2 (Appendix), p. 6. Torino. 

 Bequaert, J. C. 



1929. The insect carrier of Onchocerca volvulus in Liberia. Trans. 4th 



Internat. Congr. Ent., Ithaca, N. Y., 1928, pp. 605-607. 

 1934. In Strong, R. P. ; Sandground, J. D. ; Bequaert, J. C. ; and Ochoa, 

 M. M., "Onchocerciasis, with Special Reference to the Central 

 American Form of the Disease." Contr. No. 6, Dept. Trop. Med. 

 and Inst. Trop. Biol, and Med., Harvard Univ., 234 pp. 



