Cross-mating experiments with Boophilus annulatus and B. microplus (Acarina: Ixodidae).

Abstract

Female Boophilus annulatus (Say) and B. microplus (Canestrini) mated readily with males of the other species when pairs were isolated in a small cell on a calf's back. The crossmated females engorged as readily as females that mated with their own species, the size and fecundity of the females were not altered by cross-mating, the hatch of the F1 eggs equaled that of colony strains of the 2 species, and the F1 hybrid progeny appeared normal in vigor and longevity. However, the eggs resulting from F1 brother × sister matings generally did not hatch. Backcrosses indicated that the sterility of hybrid males exceeded 99% and that the fertility of hybrid females was reduced. The caudal process of the hybrid males was usually intermediate in size between that of normal B. annulatus and B. microplus males. The 2 species are apparently closely related, probably sibling species, but reproductively isolated by sterility of hybrids.