Biotic unpredictability and sexual reproduction: Do aphid genotype-host genotype interactions favor aphid sexuality?

The possibility that genetic variation among host plants favors sexuality in aphids is explored in the context of Williams and Mitton's (1973) aphid-rotifer model of sib competition. A survey of studies concerning plant resistance to aphids suggests that conditions favoring sexuality can occur where different aphid genotypes are adapted to different host plant species, or where major plant resistance genes differentially affect colonizing success of aphid genotypes. These phenomena are apparently uncommon, however. Thus it is unlikely that genetic heterogeneity among host plants is of major importance for the retention of sexuality in aphid life cycles.