Induction of indirect defence aganist spider-mites in uninfested lima bean leaves

Abstract

Headspace analyses of uninfested Lima bean ( Phaseolus lunatus) leaves show an absence of or only trace amounts of the terpenoids ( E)-β-ocimene and ( E)-4,8-dimethyl-1,3,7-nonatriene. Upon infestation by two-spotted spider-mites ( Tetranychus urticae), Lima bean leaves produce ( E)-β-ocimene and ( E)-4,8-dimethyl-1,3,7-nonatriene which attract predators of the herbivore, a phenomenon known as indirect defence. When uninfested Lima bean leaves were placed on wet cotton wool upon which leaves that were partially infested with spider-mites, were also placed, the uninfested leaf tissue emitted the terpenoids in relatively high amounts: ca 20–40% of the amounts emitted by the infested leaf tissue. The same effect was found when uninfested leaves were put on wet cotton wool on which infested leaves had previously lain. The data show that an elicitor(s) from spider-mite infested leaves induces the production of ( E)-β-ocimene and ( E)-4,8-dimethyl-1,3,7-nonatriene in uninfested Lima bean leaves. This is the first chemical evidence for induction of indirect defence in uninfested leaves.