Exploiting scents of distress: Herbivore-induced plant odours and the prospects of using them in the control of agricultural pests

Plants have evolved an elaborate arsenal of physical and chemical defenses that allow them to cope with their numerous attackers. An increasing number of studies suggest that, if properly understood, these natural plant defenses can be manipulated and exploited for the control of insect pests. We have been studying a form of indirect plant defense, whereby, in response to insect feeding, plants emit various volatile compounds that attract the natural enemies of their attackers. Using maize as our model plant, we recently found that these tritrophic interactions also occur belowground, where insects-damaged roots release attractants for entomophatogenic nematodes. The roots of many varieties of maize release the sesquiterpene (E)-b-caryophyllene when damaged by larvae of the ferocious western corn rootworm. Interestingly, most North-American maize varieties do not emit this signal. In field studies, the absence of the signal was shown to have major consequences for nematode attraction and resulted in dramatically lower nematode infection rates of pest larvae. Hence, the plants' natural defense signals show great potential for the enhancement of biological pest control. We have also found that endophytic bacteria can affect the volatile emissions to their advantage and that induced volatiles affect defense responses in neighboring plants. I will give an overview of our work in these areas with an emphasis on the possibility to manipulate volatile emissions in crop plants in order to enhance direct and indirect resistance against pests.