The effects of non-host volatiles on habitat location by phytophagous insects
The host-plant selection sequence of phytophagous insects can be divided into three steps: (i) habitat location, (ii) host location, and (iii) host acceptance. Chemoreception plays a main role during the process. Olfaction is typically the most important sensory modality during the first two steps, whereas contact chemoreception dominates the third. At all steps in the selection sequence, positive and negative external stimuli interact with each other and also with internal factors in the insect, and the balance between positive and negative stimuli can be tipped towards either acceptance or rejection of a particular habitat or host. Non-host volatiles (NHV) have been shown to modulate host location behaviour in several insect orders. Few studies report effects at the habitat level, but in forest ecosystems, indications of anti-attractant effects at the habitat level has been found in a small number of conifer-inhabiting coleopterans and lepidopterans. In agricultural systems, intercropping studies have frequently found lower pest insect abundance in polycultures compared to monocultures. It has been hypothesized, and sometimes demonstrated, that repellent NHV from the intercrop is the main mechanism for the observed patterns of pest abundance. However, several other mechanisms have been suggested, all discussed here. Positive and negative olfactory stimuli are perceived by olfactory hairs (sensilla), mainly located on the antennae. A brief overview of the insect olfactory system is presented and encoding of positive and negative stimuli by the peripheral and central nervous system is discussed.
Host selection; Habitat; Phytophagous; NHV; Intercropping; Insects; Olfaction; Electrophysiology; Olfactory coding
Introductory Paper at the Faculty of Landscape Planning, Horticulture and Agricultural Science
Publisher: Faculty of Landscape Planning, Horticulture and Agricultural Science, Swedish University of Agricultural Sciences
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