Seasonal variation of Boophilus microplus (Canestrini, 1887) (Acari: Ixodidae) in cattle in Minas Gerais State, Brazil.

The seasonal variation of the tick Boophilus microplus in the 'Região Metalúrgica' region of Minas Gerais state was studied using 26 Bos taurus (Holstein) x Bos indicus (Gir) calves, of which 16 animals were 3/4 Holstein x 1/4 Gir and 10 were 3/4 Gir x 1/4 Holstein. Monthly tick counts were made between March 1996 and March 1998 and, although B. microplus infestations occurred throughout the year, they were greater during the rainy season. Rainfall was the climatic factor that most affected the seasonal variation. The animals with a preponderance of Holstein blood presented infestations that were significantly (p < 0.05) greater than those of the other cross. Five of the animals (19.2%) maintained 45.5% of the parasite load of the entire group.