Pea aphids (Acyrthosiphon pisum) infected with a defensive symbiont can maintain high reproductive rate after parasitism

The pea aphid Acyrthosiphon pisum is an agricultural pest of legumes across much of temperate North America and Europe. Introductions of the aphid parasitoid wasp, Aphidius ervi, have been successful in controlling the pea aphid, however, many aphids maintain infection with a defensive secondary endosymbiont, Hamiltonella defensa, that confers varying levels of protection against these parasitoids. Aphid lines infected with H. defensa typically exhibit higher survival rates after parasitism and can also maintain relatively high reproductive rates post-parasitism. Here we examine the cost of parasitism in several aphid lines infected with H. defensa and also detail the cost to parasitoids that manage to complete development inside resistant aphids.