Do aphid soldiers elicit an immune response in victims?

Many social insect species have evolved specialized means of defense, including some aphid species.  First-instar nymphs of the social aphid, Pemphigus obesinymphae (P. obes), an aphid that forms galls on the petioles of poplars, do not have special morphological features, but still act as 'soldiers' to defend their maternal group from predators.  Here, we first demonstrate that P. obes soldiers exhibit effective defense by using their style to attack and, even, kill other insects much larger than themselves. A closely-related non-social species, Pemphigus populi-caulis (P. caulis), does not exhibit a comparably defense. This suggests that closely-related species differ substantially in the ability to deter predators.  Secondly, because attack by soldiers appears to trigger a melanization response in the surrogate predator (Drosophila), we investigated the possibility that aphid soldiers induce an immunological-like response in victims.  Using qPCR, we compared expression levels of multiple genes from the IMD, Toll and melanization pathways in Drosophila that had been attacked by P. obes soldiers, and compared these to responses when Drosophila were exposed to non-social aphids.  The expression levels were then compared to stab, gram-negative bacteria, gram-positive bacteria, and PBS controls.  These are the first experiments that explore how aphids use their styles as weapons to elicit immune responses in natural enemies.