Effects of Ingested Secondary Metabolites on the I

Authors: Angela M Smilanich Jessica Vargas Lee A Dyer M Deane Bowers

Publish Date: 2011/03/01

Volume: 37, Issue: 3, Pages: 239-245

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Abstract

We considered the effects of plant secondary metabolites on the immune response a key physiological defense of herbivores against pathogens and parasitoids We tested the effect of host plant species and ingested iridoid glycosides on the immune response of the grazing polyphagous caterpillar Grammia incorrupta Arctiidae Individuals of G incorrupta were fed either one of three plant diets with varying secondary metabolites or an artificial diet with high or low concentrations of iridoid glycosides An immune challenge was presented followed by measurement of the encapsulation response We failed to detect a significant difference in the immune response of G incorrupta feeding on diets with varying concentrations of iridoid glycosides or feeding on different host plants However the immune response was lower in caterpillars consuming the artificial diet compared to those consuming the plant diets When caterpillar performance was measured pupal weights were lower when caterpillars ingested high concentrations of iridoid glycosides due to a decrease in feeding efficiency Overall individuals of G incorrupta that consumed different plant diets exhibited a high immune response with low variation We conclude that the immune response of G incorrupta is adapted to feeding on a variety of plants which may contribute to the maintenance of this caterpillar’s polyphagous habitThis work was funded by NSF grants DEB 0614883 and CHE 0718732 as well as EarthWatch Institute funding Thanks to Michael S Singer Wesleyan University for providing caterpillars and Evan Lampert Jeff Chambers and Grant Gentry for providing comments on earlier versions of the manuscript Excellent technical assistance was provided by EarthWatch volunteers and students in the Chemical Ecology Laboratory at Tulane University

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