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  BBC 23 Nov 05
BBC listens in to insect chatter

Advanced camera and sound techniques are giving scientists remarkable new insights into insect behaviour.

Caterpillars of large blue butterflies have been shown to communicate with ants, making noises that fool them into caring for the larvae as if their own. And scientists are now looking into the idea that these sounds are actually overheard by the wasps that seek out such caterpillars to lay eggs in them.

It is one of many amazing tales to be found in TV's Life in the Undergrowth. The new BBC natural history series from Sir David Attenborough starts on Wednesday.

It shows invertebrate activity never before caught on television cameras.

"In the past, in order to get close to something, you had to pour light on it; so much so you were at risk of frying the thing - and you certainly inhibited natural behaviour," Sir David said.

"We've now got such sensitive electronic cameras that we don't need that amount of light, and we've also got tiny, tiny lenses; so we can get up close and tight, and then you see mind-blowing things."

Seek and destroy

The alcon blue butterfly (Maculinea alcon) of central Europe has long been recognised as a great con artist. Its caterpillar emits sounds and a chemical signal which essentially "instructs" worker ants to pick it up and carry it back to their nest, where it is fed, cleaned and cared for as if it were one of the queen ant's own brood.

The caterpillar can live for up to two years inside the nest before pupating into a chrysalis, from which a new butterfly emerges.

It has an enemy, however: a parasitic wasp (Ichneumon eumerus). Unlike the ants, the wasp seems to know an impostor is present and, in what appears like a kamikaze manoeuvre, will enter the nest to find the caterpillar.

Jeremy Thomas, from the Centre for Ecology and Hydrology (CEH) in Dorset, UK, has been studying large blue butterflies for over 30 years and recently discovered how this wasp avoids death by releasing a chemical signal, or pheromone, of its own.

This not only repels the ants but causes them to attack one another.

In the midst of this confusion the wasp seeks out the caterpillar and injects an egg deep inside its body. When the wasp leaves the nest everything returns to normal and the caterpillar is once again fed and cleaned by the ants.

But, when it turns into a chrysalis, it is eaten from the inside by the injected wasp grub - and it is the wasp that emerges to fly from the nest, not another alcon blue butterfly.

The right tune

Photographing all of this for TV is a first; but the great breakthrough for the scientists has been in getting clear recordings of the noises made by the blue caterpillars.

What is more, the CEH team has been able to show just what a direct effect these sounds have on the ants. "We can get clean sounds and, using miniature equipment, we can get the caterpillars and ants behaving much more naturally than in the past," Dr Thomas told the BBC News website.

"Also, we can now play the sounds back to the ants, and that shows the sounds of the caterpillar match the ant it lives with much more closely than anyone thought previously. "The ants react to the sounds in a positive way. They go to the microphones and tap them with their antennae."

But what of the wasp? The emerging hypothesis is that it hears these sounds, too. And although the ants may be fooled into thinking the caterpillar is one of their own, the wasp is not.

"The chemical signal used by the butterfly is so like the ants' own chemicals that it fools them deep down in the nest. These are not volatile chemicals either - they're ones you have to touch. So, we reason the wasp doesn't 'sniff' out the caterpillar," Dr Thomas explained.

"The sounds on the other hand are designed to travel over distances, and we suspect that's what the wasp is using."
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