The selection of larvae of Boophilus microplus infected with Babesia bovis (syn B argentina).

Observations on the dynamics of the transovarial transmission of Babesia bovis by Boophilus microplus showed that, at 28 degrees C and 90--95 per cent relative humidity, a low proportion of the eggs laid during the first five days' incubation of the engorged female ticks were infected with the Babesia. However, the eggs laid on the sixth and seventh days of incubation were heavily infected. This was the basis of a method for selecting larval cultures of B microplus which contained up to five times the infection rate of B bovis obtained if the entire egg mass of the tick were used. The technique has been used to obtain larval cultures with infection rates exceeding 20 per cent and should facilitate studies on the life cycle and immunology of the invertebrate stages of B bovis.