Host defensive behaviors and indirect competition between two parasitoids of the soybean aphid

Many herbivores use defensive behaviors to deter potential natural enemies, but not all natural enemies attack in the same way, so herbivores may detect and respond to varying threats differently. This difference in herbivore defense may complicate 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 differ in various respects; L. testaceipes is larger and more aggressive, using a simple straight ovipositor to quickly insert eggs into aphids, while B. communis is smaller and more subtle, gripping hosts for a few moments with a pair of abdominal prongs to insert an egg and paralyzing venom that leaves the aphids incapacitated for several minutes. The aphids respond differently to the two parasitoids; L. testaceipes readily elicits defensive behaviors but continues its attack despite resistance, whereas B. communis leaves its victims more placid or retreats if they retaliate. In this experiment, groups of aphids were sequentially exposed to two wasps. Defensive behaviors and their apparent success were noted, as well as the number of mummies that developed from each type of wasp.  L. testaceipes is likely to inhibit B. communis by eliciting aphid defensive behavior that interferes with B. communis oviposition, whereas B. communis is likely to enhance parasitism by L. testaceipes by leaving paralyzed and defenseless aphids in its wake. This study will elaborate how competition is impacted by specific behavioral interactions between prey and natural enemies.