For most pests, plants are just sitting targets. But while adult insects graze on their victims, some plants have fought back, entering into a pact with their pest's deadliest enemy; the plants attract parasites to prey on the adults and destroy the infestation. But if it's the younger generation of pests that does the most damage after hatching, there's no point in responding to plant alarms raised by feeding parents; the parasite must somehow reveal the location of the pest's eggs to preying parasites. Stefano Colazza and his colleagues in Italy have been analysing stinkbug eggs and broadbean leaves, to find out how they attract parasitic wasps and vanquish the pest().
First the team monitored the wasp's responses to damaged legume leaves; the wasps ignored them. But it was a different matter when the broad bean leaves already carried the pest's eggs before adult stinkbugs sucked on the sap. The parasite quickly homed in on the attractive smell, directing them to a clutch of stinkbug eggs ready to wipe out the youngsters before they had a chance to hatch. Colazza explains that annual plants, which have a short life cycle,benefit from eggtargeted parasitoid activity by nipping the pests in the bud.
