Significance of terpenoids in induced indirect plant defence against herbivorous arthropods.

Many plants respond to herbivory by arthropods with an induced emission of volatiles such as green leaf volatiles and terpenoids. These herbivore-induced plant volatiles (HIPVs) can attract carnivores, for example, predators and parasitoids. We investigated the significance of terpenoids in attracting herbivores and carnivores in two tritrophic systems where we manipulated the terpenoid emission by treating the plants with fosmidomycin, which inhibits one of the terpenoid biosynthetic pathways and consequently terpenoid emission. In the 'lima bean' system, volatiles from spider-mite-infested fosmidomycin-treated plants were less attractive to the predatory mite Phytoseiulus persimilis than from infested control plants. In the 'cabbage' system, fosmidomycin treatment did not alter the attractiveness of Brussels sprouts to two Pieris butterflies for oviposition. The parasitoid Cotesia glomerata did not discriminate between the volatiles of fosmidomycin-treated and water-treated caterpillar-infested cabbage. Both P. persimilis and C. glomerata preferred volatiles from infested plants to uninfested ones when both were treated with fosmidomycin. Chemical analysis showed that terpenoid emission was inhibited more strongly in infested lima bean plants than in Brussels sprouts plants after fosmidomycin treatment. This study shows an important role of terpenoids in the indirect defence of lima bean, which is discussed relative to the role of other HIPVs.