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Joop J.A. van Loon, Marcel Dicke
1.2.2 Searching Phase
In the searching phase, arthropods rely on optical and/or odoros infonnation
(Fig. 1 ). It is generally assumed that odors released from plant, host, or prey convey a more specific signal to the arthropod than optical cues (color, hue, contrast),
which are more uniformly distributed, especially in the plant kingdom. For several
species it has been demonstrated that both sensory modalities are employed in an
integrated way (Prokopy 1986; Aluja and Prokopy 1993; Harris and Foster 1995,).
In this chapter we will confme the discussion to chemical information.
1.2.3 Searching Mechanisms
In arthropods, the whole range of possible searching mechanisms has been found,
varying from random search to highly directed search patterns. Searching movements are considered random when frequency, rate, and direction of movement
appear unrelated to the suitability of plants, hosts, or prey that are within the perceptual range, i.e., the range within which food-derived cues are detectable by the
sensory system. During such searching, kinetic responses are commonly observed.
This searching mechanism may be the best possible when either environmental
cues provide no directionality or when the insect cannot perceive the required
stimuli.
Directed movement, on the other hand, becomes possible when the food emits
chemical cues that allow, either alone or in combination with a second cue like air
flow, a direction to be derived by the sensory system of the searching arthropod,
either by spatial or temporal comparisons of stimulus intensity or intermittency. A
commonly observed type of oriented searching mechanism is odor-conditioned
anemotaxis. Because under natural circumstances gradients in odor concentrations
are absent (Murlis et al. 1992), chemotaxis cannot be used except maybe over
distances of a few centimetres from the odor source. Anemotaxis, however, has
been demonstrated for both herbivorous and carnivorous arthropods (Fig. 1; van
Loon et al. 2000). From an evolutionary point of view, oriented search is assumed
to increase fitness as it allows a more efficient use of time and energy compared
with random search.
1.2.4 Contact Phase
Once the food is contacted, different forms of explorative behavior are exhibited
which involve repeated contacting by antennae, mouthparts, legs, and/or ovipositor that bear mechanosensory and contact-chemosensory sensilla. Only at the end
of the contact phase, does acceptance of the food source occur. At this point
mechanosensory and gustatory information have become available in addition to
Joop J.A. van Loon, Marcel Dicke
1.2.2 Searching Phase
In the searching phase, arthropods rely on optical and/or odoros infonnation
(Fig. 1 ). It is generally assumed that odors released from plant, host, or prey convey a more specific signal to the arthropod than optical cues (color, hue, contrast),
which are more uniformly distributed, especially in the plant kingdom. For several
species it has been demonstrated that both sensory modalities are employed in an
integrated way (Prokopy 1986; Aluja and Prokopy 1993; Harris and Foster 1995,).
In this chapter we will confme the discussion to chemical information.
1.2.3 Searching Mechanisms
In arthropods, the whole range of possible searching mechanisms has been found,
varying from random search to highly directed search patterns. Searching movements are considered random when frequency, rate, and direction of movement
appear unrelated to the suitability of plants, hosts, or prey that are within the perceptual range, i.e., the range within which food-derived cues are detectable by the
sensory system. During such searching, kinetic responses are commonly observed.
This searching mechanism may be the best possible when either environmental
cues provide no directionality or when the insect cannot perceive the required
stimuli.
Directed movement, on the other hand, becomes possible when the food emits
chemical cues that allow, either alone or in combination with a second cue like air
flow, a direction to be derived by the sensory system of the searching arthropod,
either by spatial or temporal comparisons of stimulus intensity or intermittency. A
commonly observed type of oriented searching mechanism is odor-conditioned
anemotaxis. Because under natural circumstances gradients in odor concentrations
are absent (Murlis et al. 1992), chemotaxis cannot be used except maybe over
distances of a few centimetres from the odor source. Anemotaxis, however, has
been demonstrated for both herbivorous and carnivorous arthropods (Fig. 1; van
Loon et al. 2000). From an evolutionary point of view, oriented search is assumed
to increase fitness as it allows a more efficient use of time and energy compared
with random search.
1.2.4 Contact Phase
Once the food is contacted, different forms of explorative behavior are exhibited
which involve repeated contacting by antennae, mouthparts, legs, and/or ovipositor that bear mechanosensory and contact-chemosensory sensilla. Only at the end
of the contact phase, does acceptance of the food source occur. At this point
mechanosensory and gustatory information have become available in addition to