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

The sheep biting louse, Bovicola ovis (Schrank), is an economically important, worldwide ectoparasite of sheep. In Australia, up to 30% of sheep flocks are infested with lice. The usual method of control has been synthetic pyrethroids applied as pour-on along the back of the sheep, but treatment failures have become widespread since 1985 because of the development of resistance. We used allozyme markers to study the distribution of genetic variation within and among populations of lice on different farms in Western Australia. Genetic variation within populations was similar to previously reported values for other ectoparasitic arthropods. Heterozygote deficiencies were found at 1 locus ina number of population acid another 2 loci in 1 other population. However, another variable locus conformed to Hardy-Weinberg equilibrium and there was little evidence of extensive linkage disequilibrium between loci, Further studies are necessary to establish the breeding system. Genetic differences among populations were not related to geographic separation, which is consistent with an island model of population structure. A small but significant proportion (2.8%) of the total genetic variation was distributed among populations' equivalent under the island model to a gene flow of 8.7 individuals exchanged per generation. The implications of this result are discussed in terms of controlling and managing synthetic pyrethroid resistance in sheep biting lice.