Genetic structure of the Bovicola ovis (Mallophaga : Trichodectidae) in southwestern Australia

The sheep biting louse, Bovicola ovis (Schrank), is an economically importa nt, worldwide ectoparasite of sheep. In Australia, up to 30% of sheep flock s are infested with lice. The usual method of control has been synthetic py rethroids applied as pour-on along the back of the sheep, but treatment fai lures have become widespread since 1985 because of the development of resis tance. We used allozyme markers to study the distribution of genetic variat ion within and among populations of lice on different farms in Western Aust ralia. Genetic variation within populations was similar to previously repor ted values for other ectoparasitic arthropods. Heterozygote deficiencies we re found at 1 locus ina number of population acid another 2 loci in 1 other population. However, another variable locus conformed to Hardy-Weinberg eq uilibrium and there was little evidence of extensive linkage disequilibrium between loci, Further studies are necessary to establish the breeding syst em. Genetic differences among populations were not related to geographic se paration, which is consistent with an island model of population structure. A small but significant proportion (2.8%) of the total genetic variation w as distributed among populations' equivalent under the island model to a ge ne flow of 8.7 individuals exchanged per generation. The implications of th is result are discussed in terms of controlling and managing synthetic pyre throid resistance in sheep biting lice.