Has the attraction of predatory coccinellids to cornicle droplets constrained aphid alarm signaling behavior?

When attacked by a predator, aphids of many species secrete cornicle drople ts, containing an alarm pheromone, that results in the dispersal of nearby conspecifics. As females are parthenogenetic, alarm signaling functions to enhance the survival of clone-mates. Enigmatically, however, aphids are phy sically able to, but usually do not emit alarm pheromone when initially det ecting a predator but rather signal only when captured by a predator We hyp othesized that cornicle droplets may be attractive to natural enemies and r esult in an increased risk of predation for the signaler thereby selecting for prudent alarm signalers. We tested this hypothesis by investigating the olfactory cues that the multicolored Asian ladybird beetle, Harmonia axyri dis Pallas, uses to locate pea aphids, Acyrthosiphon pisum. In choice tests , H. axyridis were am-acted to odors from pea aphid colonies, whether feedi ng or nor feeding on a host plant leaf; but were not attracted to cornicle droplets containing alarm pheromone. Further individual pea aphids emitting cornicle droplets were not located more often or in a shorter period of ti me by beetles than aphids nor emitting cornicle droplets. Thus, the cost of emitting early alarm signals is not prohibitively high in regards to the a ttraction of predators such as H. axyridis.