Abstract
An investigation of bovine thelaziasis and its vector was conducted by the authors in Niikappu Pasture, Hokkaido, during the period August, 1962- November, 1963. The results are as follows : 1. The flies found on cows were mainly Musca convexifrons, Morellia simplicissima, Stomoxys calcitrans and a few other species. Of these, M. convexifrons and M. simplicissima gathered around the eyes of cows and licked their tears. 2. Although 3, 923 specimens representing several species of flies were dissected, thelazian larvae were found only in females of M. convexifrons. 3. Thelazian larvae were found in females of M. convexifrons from July to October. The highest percentage of infected M. convexifrons was found in October, although the number of thelazian larvae per individual fly was greatest in September. 4. Females of M. convexifrons were dissected into four parts (proboscis, head, thorax, and abdomen). Each part was examined separately for presence of thelazian larvae. In these examinations, thelazian larvae were found most frequently and in greatest number in the abdomen. The head was second in this respect. 5. Infection rate showed a direct correlation with ovarian development in M. convexifrons. The highest infection rate was found among flies with fully developed ovaries. 6. Thelazian larvae were collected from eyes of cows throughout the year. The infection rate was highest from September to November, and lowest during May and June. 7. All adults of Thelazia collected from eyes of cows were identified as Thelazia rhodesi (Desmarest, 1827).
