Document: STE-3-48-12

Turning the tides: Gall-insects benefit from plant defense biochemistry.

ALLISON, S.D.* ¹ and J.C.SCHULTZ ²

Stanford University, Stanford, CA 94305-5020, USA ¹
Pennsylvania State University, University Park, PA 16802, USA ²

Abstract:
We performed enzymatic and histochemical assays of gall tissue and adjacent leaf tissue in two oak species to determine if gall structures possess unique biochemical compositions that could facilitate gall-insect growth and development. Galls of the cynipid wasp Andricus petiolicolus on chestnut oak (Quercus prinus) had significantly greater peroxidase and invertase activities and lower antioxidant potential relative to host leaves. As compared to the surrounding gall tissue, the nutritive tissue (eaten by the insect) had a 5-6 fold greater protein concentration but lower peroxidase activity and polyphenol content. A. petiolicolus galls and galls of 12 other species from red oak (Quercus rubra) contained different peroxidase isozyme activities and lower protein concentrations in relation to their host leaves. To determine if gall-insect success is influenced by the status of the host leaf, we wounded galled chestnut oak leaves with gypsy moth larvae (GML) and sprayed them with the wounding-associated plant hormone jasmonic acid (JA). Although short-term wounding with GML was not sufficient to induce changes in foliar biochemistry, chronic application of JA resulted in significantly lower foliar protein concentrations and increased activities of wounding-inducible enzymes. These changes in the host leaves, however, had no effect on A. petiolicolus success, measured as percent emergence from galls. Thus, biochemical patterns typically associated with plant defense (i.e. more defensive enzymes and polyphenols, less protein content) are present in galls and can be induced in host leaves but do not reduce gall-insect success. Rather, gall-insects appear to buffer themselves against negative plant responses. Gall biochemical composition is manipulated by the insect to provide nutrition while resisting herbivory, pathogens, and changes in the biochemistry of the host leaf.

Keywords: plant-insect interactions, Quercus, gall-insect, plant defense

This abstract is being presented at: 3:45 PM in session:
Oral Session #15: Parasitoids and Diseases.