Complexity of plant volatile-mediated interactions beyond the third trophic level

Food chains of plant-associated communities typically reach beyond three trophic levels. The predators and parasitoids in the third trophic level are under attack by top predators or parasitised by hyperparasitoids. These higher trophic level organisms respond to plant volatiles in search of their prey or host. Thereby, plant volatiles affect community processes such as competition and intraguild predation among predators and parasitoids at the terminal end of the food chain. The response of fourth trophic level organisms to plant volatiles potentially reduces the benefit of these volatiles as indirect defence for the plant. In the application of parasitoids as biological control agents of herbivore pests, hyperparasitoids may diminish the effectiveness of parasitoids. Detailed understanding of the use of plant odours by hyperparasitoids may provide tools to further optimise biological control