Hunting behavior and competition of two parasitoids of the soybean aphid

Many herbivores use defensive behaviors to deter potential natural enemies. But natural enemy attack behavior varies, and herbivores can defend themselves differently in response. This flexibility in herbivore defense complicates competitive interactions between different natural enemies. The soybean aphid, Aphis glycines, is susceptible to both the native parasitoid Lysiphlebus testaceipes and the introduced parasitoid Binodoxys communis. These two parasitoids are morphologically and behaviorally distinct, and elicit different responses from their aphid hosts. In this experiment, groups of aphids were sequentially exposed to two wasps. Aphid defensive behaviors and the wasps’ apparent sting success were compared.  Compared to stinging naïve aphids that had never encountered parasitoids, L. testaceipes stings far more rapidly following a B. communis attack on the colony and far less rapidly following an attack from a different L. testaceipes on the colony. The sting rate of B. communis, on the other hand, was not affected by recent aphid exposure to either species of wasp. This suggests that host defensive response to a parasitoid, and the parasitoid’s response to defensive behavior, can mediate competition between parasitoids.