Meta-analysis of laboratory experiments on plant-plant information transfer

Field and laboratory experiments on chemical information transfer between damaged and undamaged plants have provided variable results. Here. we report on laboratory assays on the responses of plants exposed to volatiles released from plants infested by spider mites (Tetranychus urticae). Signal-sending and receiving plants (Lima bean, cotton, cucumber and tomato) were either conspecific or heterospecific. To measure the reaction of the receiver in terms of signal release. we used predatory mites (Phytoseiulus persimilis) as an olfactory sensor and tested their behavioural response to the released signals. The results show that intraspecific, as well as interspecific plant-plant information transfer occurs. However, plants are only weakly attractive to predators immediately after taking them away from exposure to herbivore-induced plant volatiles (HIPV), but become significantly more attractive somewhere within a period of ca. 2 days. No evidence was found that HIPV-exposed plants exhibit intensified signal release by the time they are actually attacked by herbivorous mites. Taken together. the predator responses to odour from plants previously exposed to HIPV. were significant, but weak. We argue that weak responses in the laboratory do not necessarily imply trivial phenomena in the field. (C) 2001 Elsevier Science Ltd. All rights reserved.