Scanning electron microscopic study of third-instar warbles in yak in China.

Scanning electron microscopic observations were performed to compare the structures of third-instar of three species of warbles (Hypoderma bovis, H. lineatum and H. sinense) that infest yak in China. The heads of the warbles consisted of mouths and opercular sutures with spinal bands between them. We could not detect any morphological differences in the shape of the warble's heads among these three species. The spiracular plate of H. bovis was strongly concaved and had numerous spines at the spiracular opening rims. The H. lineatum had flat spiracular plates and no spines on the spiracular plates. In the case of H. sinense the spiracular plate was as flat as that of H. lineatum but had small sized and fewer spines on the spiracular plates. At the ventral side on the tenth segment of the warble body of H. bovis the spinal band was absent. Although H. lineatum had only one band at the posterior border on the tenth ventral segment, H. sinense had two bands of spines at the anterior and posterior border on the tenth segment.

Migration of warble fly larvae in the yak and optimum timing of ivermectin treatment.

Sixty yaks were autopsied to determine the migration pattern of warble fly larvae. In August, first instars were observed in the body of yak for the first time. These larvae peaked in number in October. From November to February, second instars were detected and their number peaked in January. Third instars appeared in January and peaked in March. Forty-five yaks were administered with ivermectin: 15 animals in September, 15 in October and 15 in November. Between December and June, the number of warbles was checked by palpation. Although some warbles were observed in the September- and November-treated groups, no warbles were detected in the October-treated group. Treatment of yaks with ivermectin was most effective for warble fly in October.