Sex Ratios of Boophilus Ticks (Acari: Ixodidae) Reaching Adulthood on Cattle

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Abstract
The sex ratios were determined for Boophilus microplus (Canestrini), B. annulatus (Say), and hybridized Boophilus ticks reaching the adult stage on cattle. The sex ratios (females to males) of B. microplus and B. annulatus were 1.36:1 and 1.35:1, respectively. In a hybrid of these two species, the ratio was 1.20:1. Thus, proportionately more hybrid males reached adulthood than in either pure strain. The proportion of male hybrids reaching adulthood may have been the result of hybrid vigor. The fact that more females than males reached adulthood in the three types of ticks is probably because these ticks have an XX-XO sex-determining mechanism. Any recessively lethal mutations occurring on the X chromosome, therefore, will be expressed in the male but not in the female unless it is homozygous recessive for the lethal trait. The presence of more hybrid males is discussed with respect to their potential use in a control strategy against Boophilus ticks.