Treacherous Wasps Turn Ant Against Ant

Triangle of deceit. A wasp examines a caterpillar before laying eggs, ignoring a worker ant that is biting its leg.

The natural world abounds with trickery. Take for instance the large blue butterfly Maculinea rebeli: Its caterpillars adopt chemical camouflage to manipulate red ants into feeding, grooming, and protecting them. But the caterpillars aren't the only ones to play the ants for fools, a new study reveals. A wasp, invading ant nests to parasitize the parasitic caterpillars inside, avoids ant attacks by deploying chemicals that provoke the ants into attacking one another.

In European grasslands, Maculinea caterpillars fall off their host plants partway through development and attract red ants, which carry them to their nests. There the caterpillars, protected by chemicals that mimic those of ant larvae, are fed and tended by adult ants. Meanwhile, the wasp Ichneumon eumerus comes calling. It lays eggs in the caterpillars; the wasp larvae feed off the caterpillars and hatch during their pupation. They then leave the nest, soon ready to mate and find more nest-bound caterpillars. But how the wasps get in and out of the nest without being killed by the ants has been a mystery.

In the 30 May issue of Nature, ecologists Jeremy Thomas and Graham Elmes of the Centre for Ecology and Hydrology in Dorset, United Kingdom, and colleagues reveal the wasps' trick. The researchers isolated and synthesized six chemicals that the wasps secrete--four of them new to science. Experiments in the lab showed that these chemicals whip the ants into a frenzy, wildly biting and stinging one another--providing a distraction that allows adult wasps to enter nests and hatching wasps to escape.

The research may have a commercial application. The compounds discovered have the longest carbon chains of any known mimic of ant alarm pheromones, making them minimally volatile and allowing them to persist for up to 50 days. Similar chemicals could be used for pest control measures against ants, the authors suggest. The work also has conservation relevance, as both the wasp and the caterpillar are endangered. "It is frightening to think that ... [chemicals] that could be so valuable could so easily have been lost," says chemical ecologist Graeme Jones of Keele University in Staffordshire, U.K.

Related site
Overview of Thomas and Elmes's research

Follow News from Science