Induction of Plant Volatiles by Herbivores with Different Feeding Habits and the Effects of Induced Defenses on Host-Plant Selection by Thrips |
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Authors: | Casey M Delphia Mark C Mescher Consuelo M De Moraes |
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Affiliation: | (1) Department of Entomology, The Pennsylvania State University, 535 ASI Building, University Park, PA 16802, USA |
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Abstract: | Induced plant responses to attack by chewing insects have been intensively studied, but little is known about plant responses
to nonchewing insects or to attack by multiple herbivores with different feeding habits. We examined volatile emissions by
tobacco, Nicotiana tabacum, in response to feeding by the piercing–sucking insect western flower thrips (WFT), Frankliniella occidentalis, the chewing herbivore Heliothis virescens, and both herbivores simultaneously. In addition, we examined the effects of herbivore-induced plant defenses on host-plant
selection by WFT. Plants responded to thrips feeding by consistently releasing five compounds. Simultaneous feeding by WFT
and H. virescens elicited the same 11 compounds emitted in response to caterpillar feeding alone; however, two compounds, α-humulene and caryophyllene
oxide, were produced in greater amounts in response to simultaneous herbivory. In choice tests, thrips consistently preferred
uninduced plants over all other treatments and preferred plants damaged by caterpillars and those treated with caterpillar
saliva over those treated with caterpillar regurgitant. The results are consistent with a previous finding that caterpillar
regurgitant induces the release of significantly more volatile nicotine than plants damaged by caterpillars or plants treated
with caterpillar saliva. A repellent effect of nicotine on WFT was confirmed by encircling unwounded plants with septa releasing
volatile nicotine. Our results provide the first direct evidence that thrips feeding induces volatile responses and indicates
that simultaneous herbivory by insects with different feeding habits can alter volatile emissions. In addition, the findings
demonstrate that induced plant responses influence host-plant selection by WFT and suggest that the induction of volatile
nicotine may play a role in this process. |
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Keywords: | Plant– insect interactions Induced defenses Plant volatiles Simultaneous herbivory Ovipositional preference Insect behavior Host-plant selection Frankliniella occidentalis Heliothis virescens Nicotiana tabacum Nicotine |
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