Abstract
Plant chemical defenses can affect herbivores directly or indirectly through the emission of herbivore-induced plant volatiles (HIPVs) that recruit natural enemies. Corn seedlings have high concentrations of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) that deter aphids, but as concentration decreases over the course of plant phenology, plants become less resistant. We investigated whether corn phenological stage influences the attractiveness of Rhopalosiphum maidis (Fitch, 1856) - infested corn seedling volatiles to the predatory lacewing Chrysoperla externa (Hagen, 1861). In olfactometer, lacewings preferentially oriented to volatiles from aphid-infested over those by uninfested corn seedlings at V6 or V7 stages, but did not discriminate between volatiles from uninfested and aphid-infested V5-stage seedlings. Greater numbers of aphids died in V5 corn seedlings relative to those in V6 and V7 seedlings. Our results indicate that the lack of discrimination of the predatory lacewing to HIPVs emitted by V5 corn seedlings is due to insufficient induction given that they were more resistant to R. maidis.
Highlights
Plant chemical defenses can affect herbivores directly or indirectly through the emission of herbivore-induced plant volatiles (HIPVs) that recruit natural enemies
Induced plant defenses comprise increased concentrations of constitutive defensive metabolites or novel compounds that directly act against herbivores by altering their physiology and behavior, or indirectly by attracting herbivore natural enemies (Dicke 1999, Turlings & Wäckers 2004)
This compound is well-known for its role in deterring herbivory by aphids, especially the corn aphid Rhopalosiphum maidis (Fitch, 1856) (Hemiptera: Aphididae), an important pest of corn crops, that is sensitive to DIMBOA and avoids feeding on corn genotypes with high levels of DIMBOA (Niemeyer et al 1989, Givovich & Niemeyer 1995)
Summary
Plant chemical defenses can affect herbivores directly or indirectly through the emission of herbivore-induced plant volatiles (HIPVs) that recruit natural enemies. We investigated whether phenological stage of corn seedlings affects the attraction of the predatory lacewing Chrysoperla externa (Hagen, 1861), which is a generalist natural predator of aphids, to the volatile emission of corn plants infested with R. maidis. We tested the olfactory response of lacewing larvae to volatiles emitted by V5 to V7 corn seedlings and registered the mortality of R. maidis on those plants.
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