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Joop J.A. van Loon, Marcel Dicke
predators, 25% are paras ito ids, 10% are scavengers and 15% are tourists (nonpredatory arthropods having no intimate or lasting association with the plant;
Moran and Southwood 1982). In terms of biomass, herbivores represent 54%. A
prominent feature of plant utilization by herbivorous arthropods is the dominance
of dietary specificity. Over 80% of the herbivorous species for which the host
plant range is well documented are specialist feeders, confining their food intake to
a few closely related plant species (monophagous) or to plant species belonging to
one or a few phytochemically similar plant families (oligophagous) (Schoonhoven
et al. 1998). The remainder has generalist or polyphagous feeding habits,
accepting dozens of plant species belonging to unrelated families, though certainly
not all plant species offered. Similarly, carnivorous species differ largely in their
dietary range.
Most parasitic carnivorous species are specialized on a limited range of host
species, while predatory species are generally less specialized (Slansky and Rodriguez 1987) yet prey preferences are found (Dicke et al. 1988) and several species
of specialized predators have been documented (Sabelis 1992). The interactions
between herbivorous insects and plants have long been considered from a bilateral
perspective. From a trophic point of view this seems adequate but from an informational point of view a proper understanding of herbivore food selection behavior necessitates the study of effects of signals from competing herbivores and
natural enemies as well (Dicke 2000). Likewise, over the past decade it has
become clear that the food searching and acceptance behavior of carnivorous
arthropods can only be understood from a multitrophic perspective (Vet and Dicke
1992; Turlings et al. 1993; Dicke and Vet 1999; Sabelis et al. 1999).
1.2 Sensory Information for Food Selection Behavior
1.2.1 Behavioral Chains
A description of the behavior leading to food intake or oviposition takes the form
of a fixed sequence of distinct behavioral elements during which the insect
responds to a succession of stimuli of different modalities. When the outcome of
sensory evaluation is to reject the particular plant, prey or host as food or as
oviposition site, the animal may "jump back" to one of the earlier steps in the
sequence. Modification of selection behavior as a result of previous experience
can be observed as faster decision making or as changes in preference, but the
sequence remains the same. Such sequences of behavioral phases and of elements
within each phase can be quite elaborate. Examples of sequences displayed by a
parasitoid and a predator are given in Fig. 1.
The sequence of food selection behavior can be subdivided into two main consecutive phases: (1) searching and (2) contact-testing. The searching phase ends by
establishing contact with the host plant, host insect, or prey, the second phase ends
by actual ingestion of plant or insect material or with the deposition of eggs. Going
Joop J.A. van Loon, Marcel Dicke
predators, 25% are paras ito ids, 10% are scavengers and 15% are tourists (nonpredatory arthropods having no intimate or lasting association with the plant;
Moran and Southwood 1982). In terms of biomass, herbivores represent 54%. A
prominent feature of plant utilization by herbivorous arthropods is the dominance
of dietary specificity. Over 80% of the herbivorous species for which the host
plant range is well documented are specialist feeders, confining their food intake to
a few closely related plant species (monophagous) or to plant species belonging to
one or a few phytochemically similar plant families (oligophagous) (Schoonhoven
et al. 1998). The remainder has generalist or polyphagous feeding habits,
accepting dozens of plant species belonging to unrelated families, though certainly
not all plant species offered. Similarly, carnivorous species differ largely in their
dietary range.
Most parasitic carnivorous species are specialized on a limited range of host
species, while predatory species are generally less specialized (Slansky and Rodriguez 1987) yet prey preferences are found (Dicke et al. 1988) and several species
of specialized predators have been documented (Sabelis 1992). The interactions
between herbivorous insects and plants have long been considered from a bilateral
perspective. From a trophic point of view this seems adequate but from an informational point of view a proper understanding of herbivore food selection behavior necessitates the study of effects of signals from competing herbivores and
natural enemies as well (Dicke 2000). Likewise, over the past decade it has
become clear that the food searching and acceptance behavior of carnivorous
arthropods can only be understood from a multitrophic perspective (Vet and Dicke
1992; Turlings et al. 1993; Dicke and Vet 1999; Sabelis et al. 1999).
1.2 Sensory Information for Food Selection Behavior
1.2.1 Behavioral Chains
A description of the behavior leading to food intake or oviposition takes the form
of a fixed sequence of distinct behavioral elements during which the insect
responds to a succession of stimuli of different modalities. When the outcome of
sensory evaluation is to reject the particular plant, prey or host as food or as
oviposition site, the animal may "jump back" to one of the earlier steps in the
sequence. Modification of selection behavior as a result of previous experience
can be observed as faster decision making or as changes in preference, but the
sequence remains the same. Such sequences of behavioral phases and of elements
within each phase can be quite elaborate. Examples of sequences displayed by a
parasitoid and a predator are given in Fig. 1.
The sequence of food selection behavior can be subdivided into two main consecutive phases: (1) searching and (2) contact-testing. The searching phase ends by
establishing contact with the host plant, host insect, or prey, the second phase ends
by actual ingestion of plant or insect material or with the deposition of eggs. Going