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Joop J.A. van Loon, Marcel Dicke
specific volatiles. In generalists a weak or no attraction is seen, whereas in several
instances generalist herbivores are repelled by these infochemicals.
The generally occurring GLVs often attract both specialists and generalists. For
several specialist herbivores, despite explicit attempts no taxon-specific plant
volatiles were found that could act as kairomones. As emission patterns of GLVs
differ quantitatively between plant taxa, it is conceivable that information on the
ratio of these generally occurring components is conveying information with
sufficient specificity. The Colorado potato beetle seems to make use of such
information during its odor-conditioned anemotactic response to potato plants;
individual GLVs added in excess amounts to the total blend abolished its
anemotactic response (Visser and Ave 1978).
2.3.2 Responses of Herbivores to Volatiles from Damaged Plants
When the role of plant volatiles for host-plant location by herbivores is
investigated, compounds are commonly collected as the headspace of intact plants.
However, under field conditions most, if not all, plants experience damage or
infection. These are known to result in volatile emissions which in several cases
differ qualitatively from those of intact plants (Dicke 2000).
Different species of herbivorous arthropods indeed respond differently to the
volatile bouquets emitted by damaged plants. Some species avoid plants damaged
by conspecific or heterospecific herbivores, while others are attracted to such
plants (reviewed by Dicke and Vet 1999). These differences in behavioral
responses between species might be correlated with adaptations to the dominant
ecological constraints imposed upon them. Avoidance of damaged plants may be
functional to avoid competition, while attraction, leading to aggregated feeding,
may be adaptive as a strategy of overwhelming induced plant defence.
2.4 Responses to Volatile Plant Infochemicals: Carnivores
2.4.1 Detectability and Reliability of Plant-Produced Olfactory Information
In their search for herbivorous prey, carnivorous arthropods are confronted with
the problem of locating small organisms hidden in a large green biomass. As
argued by Vet and Dicke (1992), carnivores face a reliability-detectability
problem. Although volatile chemical information emitted by plants is abundantly
available in the environment and thus readily detectable, the reliability in signaling
the presence of herbivorous hosts or prey feeding somewhere in the vegetation is
limited. Conversely, volatiles emitted by the prey or host are reliable signals but
are embedded in the much larger amounts of plant volatiles. In contrast, it is well
established for a range of tritrophic systems that the plant is the source of volatile
Joop J.A. van Loon, Marcel Dicke
specific volatiles. In generalists a weak or no attraction is seen, whereas in several
instances generalist herbivores are repelled by these infochemicals.
The generally occurring GLVs often attract both specialists and generalists. For
several specialist herbivores, despite explicit attempts no taxon-specific plant
volatiles were found that could act as kairomones. As emission patterns of GLVs
differ quantitatively between plant taxa, it is conceivable that information on the
ratio of these generally occurring components is conveying information with
sufficient specificity. The Colorado potato beetle seems to make use of such
information during its odor-conditioned anemotactic response to potato plants;
individual GLVs added in excess amounts to the total blend abolished its
anemotactic response (Visser and Ave 1978).
2.3.2 Responses of Herbivores to Volatiles from Damaged Plants
When the role of plant volatiles for host-plant location by herbivores is
investigated, compounds are commonly collected as the headspace of intact plants.
However, under field conditions most, if not all, plants experience damage or
infection. These are known to result in volatile emissions which in several cases
differ qualitatively from those of intact plants (Dicke 2000).
Different species of herbivorous arthropods indeed respond differently to the
volatile bouquets emitted by damaged plants. Some species avoid plants damaged
by conspecific or heterospecific herbivores, while others are attracted to such
plants (reviewed by Dicke and Vet 1999). These differences in behavioral
responses between species might be correlated with adaptations to the dominant
ecological constraints imposed upon them. Avoidance of damaged plants may be
functional to avoid competition, while attraction, leading to aggregated feeding,
may be adaptive as a strategy of overwhelming induced plant defence.
2.4 Responses to Volatile Plant Infochemicals: Carnivores
2.4.1 Detectability and Reliability of Plant-Produced Olfactory Information
In their search for herbivorous prey, carnivorous arthropods are confronted with
the problem of locating small organisms hidden in a large green biomass. As
argued by Vet and Dicke (1992), carnivores face a reliability-detectability
problem. Although volatile chemical information emitted by plants is abundantly
available in the environment and thus readily detectable, the reliability in signaling
the presence of herbivorous hosts or prey feeding somewhere in the vegetation is
limited. Conversely, volatiles emitted by the prey or host are reliable signals but
are embedded in the much larger amounts of plant volatiles. In contrast, it is well
established for a range of tritrophic systems that the plant is the source of volatile