Adaptive sex-ratio manipulation in Pediculus humanus capitis: possible interpretations of Buxton's data.

The sex-ratio pattern of an exceptional population of human head lice (collected in the Colombo Prison, Ceylon, in 1934 to 1936) was found to be consistent with a current hypothesis on adaptive sex-ratio manipulation. Data suggest that the louse burdens were isolated and, therefore, small burdens were inbred. Thus, local mate competition favored females that produced offspring with a female bias. This is the first report to suggest that anopluran lice are capable of adaptive sex-ratio manipulation.