Eb. Mondor et Bd. Roitberg, Has the attraction of predatory coccinellids to cornicle droplets constrained aphid alarm signaling behavior?, J INSECT B, 13(3), 2000, pp. 321-329
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.