Patterns of genetic variation among canadian populations of the bird cherry-oat aphid, rhopalosiphum padi l. (homoptera: Aphididae)

Abstract

Past allozyme studies have shown a very low level of genetic variation among aphid populations. Attempts have been made to link this lack of diversity to the biological characteristics of aphids. This study examines the effect of host-alternation on genetic diversity in Canadian populations of the aphid Rhopalosiphum padi. Allozyme analysis of 15 populations on the primary host and 14 on the secondary hosts revealed polymorphism at only three of 51 loci. Little geographical differentiation was observed among populations from a single host category. However, gene frequency differences were noted between populations on primary and those on secondary hosts at two of three polymorphic loci and the mean heterozygosity was substantially reduced on secondary hosts. This pattern might result from the admixture on secondary hosts of resident clones and relatively invariant migrants from southern areas. Alternatively, the decreased heterozygosity might result from either a selective disadvantage of heterozygotes on secondary hosts or their selective migration to other hosts. © The Genetical Society of Great Britain.