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.