SCIENTISTS at Harpenden's Rothamsted Research have been discovering how plants can subtly change their smell in their own interests.

Signal grass, an important livestock food in Africa, emits a particular odour when under attack by a harmful species of stem-boring moth to deter them.

But the Harpenden scientists have found that when the moths are laying eggs, the smell changes to an odour which encourages wasps to protect the grass by attacking the moths.

Researcher Toby Bruce said "These wasps are important natural enemies of the stem-borer pest studied. They have evolved chemosensory systems that are fine-tuned for recognition of plant odours that signal the presence of their prey.

"Even though overall odour emission was reduced the wasps were more attracted to the odour of plants with eggs that the odour of plants without eggs.

"It is quality not quantity that is important in these interactions."

The discovery could be used to breed crop varieties that have better natural protection against the moths, of vital importance to impoverished farmers who can't afford herbicide.