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The summer mastitis pathogens Actinomyces pyogenes, Peptococcus indolicus, Bacteroides melaninogenicus ss. levii, Fusobacterium necrophorum and Streptococcus dysgalactiae were isolated from the polyphagous symbovine dipterans Hydrotaea irritans (Fallén) and Morellia sp. caught around dairy heifers on pasture, but not from the haematophagous species Haematobia irritans (L.), Haematobosca stimulans (Meigen), Culicoides sp. and Simulium sp. Secretions from clinical cases of summer mastitis proved to be sources of summer mastitis bacteria for more than 3 weeks despite antibiotic treatment and teat amputation. Taking into account the seasonal activity pattern of Hydrotaea irritans and its topographical distribution on grazing cattle, it appears evident that this fly may play a central role in the establishment and maintenance of the bacterial contamination with summer mastitis pathogens on the teats of healthy cattle. In the present study the survival of A.pyogenes and P.indolicus for 7 days in experimentally infected Hydrotaea irritans, as demonstrated by the recovery of these microorganisms from agar plates exposed to live infected flies, is described. However, experimental transmission of summer mastitis from sick to healthy heifers by Hydrotaea irritans proved unsuccessful.

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The study comprises 136 strains of Corynebacterium pyogenes originating from cattle (105), swine (20) , sheep (1), and insects (10). For comparison 2 strains of human origin and 1 strain of Corynebacterium hemolyticum were examined.One of the bovine strains was atyp ical, being gelatinase-negative, otherwise the strains of Cb. pyogenes were found to be biochemically identical apart from minor deviations in fermentation patterns (Table 1) . Neither were antigenic differences demonstrated (gel diffusion analyses, Figs. 1 and 2).Both of the human strains agreed biochemically with Cb. pyogenes (Table 1). By gel diffusion cross analyses one of them was found to be identical with Ch, pyogenes, the other not, though antigenically related to it (Fig. 2) .Cb. hemolyticum deviated biochemically as well as serologically from Cb, pyogenes, but the 2 organisms shared antigenic determinants (Fig. 3).