Chemical ecology of host-plant selection by herbivorous arthropods: a multitrophic perspective

Most herbivorous arthropods are specialists that feed on one or a few relat ed plant species. To understand why this is so, both mechanistic and functi onal studies have been carried out, predominantly restricted to bitrophic a spects. Host-selection behaviour of herbivorous arthropods has been intensi vely studied and this has provided ample evidence for the role of secondary plant chemicals as source of information in behavioural decisions of herbi vores. Many evolutionary studies have regarded co-evolution between plants and herbivores to explain the diversity of secondary plant chemicals and ho st specialisation of herbivores. However, many cases remain unexplained whe re: herbivores select host plants that are suboptimal in terms of fitness r eturns. A stimulating paper by Bernays and Graham [(1988) Ecology 69, 886-8 92)] has initiated a discussion on the need of a multitrophic perspective t o understand the evolution of host-plant specialisation by herbivorous arth ropods. However, this has hardly resulted in ecological studies on host-sel ection behaviour that take a multitrophic perspective. Yet, evidence is acc umulating that constitutive and induced infochemicals from natural enemies and competitors can affect herbivore behaviour. These cues may constitute i mportant information on fitness prospects, just as plant cues can do. In th is paper I selectively review how information from organisms at different t rophic levels varies in space and time and how herbivores can integratively exploit this information during host selection. In doing so, research area s are identified that are likely to provide important new insights to expla in several of the questions in herbivore host selection that remain unanswe red so far. These research areas are at the interface of evolutionary ecolo gy, behavioural ecology and chemical ecology. (C) 2000 Elsevier Science Ltd . All rights reserved.