PLANTS release chemical defences within seconds of detecting an insect鈥攅ven if the hapless diner has yet to take a bite. The fast response shows that plants are reacting to an insect鈥檚 footsteps alone.
Alan Bown and his colleagues at Brock University in Ontario let caterpillars of the tobacco budworm moth crawl across soya and tobacco leaves. Twenty seconds after a caterpillar had passed, the plants produced the toxic chemical superoxide where it trod. 鈥淲e see a track of footprints across the leaf,鈥� says Bown, who presented his results at the Society for Experimental Biology meeting in Swansea this week. He thinks the plants must detect the unique effect of suction pads on the invaders鈥� feet.