Sensory Ecology of Arthropods Utilizing Plant Infochemicals
257
olfactory information (Fig. 1 ). The accumulation of volatile and contact chemical
information has reached its maximum. The final decision is in the majority of cases
based on taste information. This is apparent from the acceptance of artificial
substrates containing nonvolatile cues devoid of naturally occurring optical,
odoros or mechanosensory cues. The crucial role of contact chemoreception in
host-plant selection of herbivorous insects has recently been reviewed by Bemays
and Chapman (1994), van Loon (1996), and Schoonhoven et al. (1998). In this
chapter we will confme the discussion to the use of olfactory information during
the searching phase.
2 Chemoreception of Volatile Plant Infochemicals by
Arthropods
2.1 Diversity and Taxonomic Patterns of Chemical Signals
Produced by Plants
Plants offer a huge biochemical diversity to herbivorous arthropods. Over I 00,000
different low molecular weight (MW < 1000 Da) organic chemicals have been
identified thus far from plants (Buckingham 1993) and this number is rapidly
increasing. Parasitic and predatory arthropods are potentially confronted with an
even greater diversity of compounds as they encounter plant compounds as well as
those produced by their hosts or prey. Although much less is known about the
chemistry of arthropod-produced chemicals than about plant-produced chemicals,
this seems not so much due to the scarcity of new chemicals that could be detected
in arthropods but rather to the technical difficulty to obtain sufficient quantities for
chemical identification.
The chemical fingerprints, either as bouquets of volatiles or as mixtures of nonvolatile compounds present on the surface or in the interior of plants, hosts, or
prey, can be extremely complex in a qualitative sense, in terms of total number of
compounds and chemical classes represented, and also variable in the quantitative
sense, due to differences in the ratios in which they can occur in the mixtures. For
plants, taxonomic patterns in nonvolatile chemistry can be discerned.
Most plan families are characterized by nonvolatile secondary plant
substances that do not occur in other families. For example, Brassicaceae and other
families belonging to the order Capparales contain glucosinolates, a family of over
100 different sulfur-containing glycosides that are toxic to many animals (Chew
1988).
The family of Solanaceae contains a group of steroid alkaloids which seem to
occur uniquely in this family (Ripperger and Schreiber 1981 ). These two families
can unambiguously be told apart by phytochemical analysis, which is feasible for
many other families as well (Hegnauer 1962-1994). For this particular example,
the chemical distinction would also tum up from analyses of the volatile
compounds as Brassicaceae produce hydrolysis products of glucosinolates called
257
olfactory information (Fig. 1 ). The accumulation of volatile and contact chemical
information has reached its maximum. The final decision is in the majority of cases
based on taste information. This is apparent from the acceptance of artificial
substrates containing nonvolatile cues devoid of naturally occurring optical,
odoros or mechanosensory cues. The crucial role of contact chemoreception in
host-plant selection of herbivorous insects has recently been reviewed by Bemays
and Chapman (1994), van Loon (1996), and Schoonhoven et al. (1998). In this
chapter we will confme the discussion to the use of olfactory information during
the searching phase.
2 Chemoreception of Volatile Plant Infochemicals by
Arthropods
2.1 Diversity and Taxonomic Patterns of Chemical Signals
Produced by Plants
Plants offer a huge biochemical diversity to herbivorous arthropods. Over I 00,000
different low molecular weight (MW < 1000 Da) organic chemicals have been
identified thus far from plants (Buckingham 1993) and this number is rapidly
increasing. Parasitic and predatory arthropods are potentially confronted with an
even greater diversity of compounds as they encounter plant compounds as well as
those produced by their hosts or prey. Although much less is known about the
chemistry of arthropod-produced chemicals than about plant-produced chemicals,
this seems not so much due to the scarcity of new chemicals that could be detected
in arthropods but rather to the technical difficulty to obtain sufficient quantities for
chemical identification.
The chemical fingerprints, either as bouquets of volatiles or as mixtures of nonvolatile compounds present on the surface or in the interior of plants, hosts, or
prey, can be extremely complex in a qualitative sense, in terms of total number of
compounds and chemical classes represented, and also variable in the quantitative
sense, due to differences in the ratios in which they can occur in the mixtures. For
plants, taxonomic patterns in nonvolatile chemistry can be discerned.
Most plan families are characterized by nonvolatile secondary plant
substances that do not occur in other families. For example, Brassicaceae and other
families belonging to the order Capparales contain glucosinolates, a family of over
100 different sulfur-containing glycosides that are toxic to many animals (Chew
1988).
The family of Solanaceae contains a group of steroid alkaloids which seem to
occur uniquely in this family (Ripperger and Schreiber 1981 ). These two families
can unambiguously be told apart by phytochemical analysis, which is feasible for
many other families as well (Hegnauer 1962-1994). For this particular example,
the chemical distinction would also tum up from analyses of the volatile
compounds as Brassicaceae produce hydrolysis products of glucosinolates called