The one-host cattle tick Boophilus mtcroplus has constituted a threat to Australia’s cattle industry ever since it was introduced almost a century ago from Java (Seddon,1968). Its origin is uncertain, but undoubtedly the tick and Zebu(Bos indicus) cattle have been associated for many thousands of years in Asia and a state of equilibrium between host and parasite has evolved. In Malaysia, Thailand and the Philippines, Bos indicus cattle are infested with small numbers (usually less than ten engorged females per animal) of B. microplus (R.H. Wharton, unpublished). This level of infestation is evidently sufficient to maintain transmission of Babesia argentina andB. bigemina since these blood parasites are present in the indigenous cattle and cause serious clinical disease in imported non-immune Bos taurus dairy cattle in Asia (Legg, 1959).