Lignin modification has no effect on insect herbivores’ feeding preferences

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ANNUAL REPORT 2005

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Photo: Tiina Ylioja

Along with cellulose and hemicellulose, lignin is one of the main components of the cell wall in wood. The chemical structure of lignin in deciduous wood can be modified through transgenic methods. This affects, among other things, the solubility of lignin in chemical pulp manufacturing. In broad-leaved trees the lignin structure comprises mainly syringyl and guaiasyl units and especially the syringyl units improve lignin’s solubility.

In this experiment, the O-methyltransferase gene controlling the formation of the syringyl units was transferred from quaking aspen (Populus tremuloides) into silver birch (Betula pendula Roth). Two of the resulting transgenic birch lines showed a significant reduction in the syringyl/guaiasyl ratio (S/G) compared to non-transgenic control birches.

Laboratory experiments were performed with insect herbivores to study how chemically modified lignin affects the feeding preferences of lepidopteran larvae (Trichopteryx carpinata, Cleora cinctaria, and Aethalura punctulata) and the adults of birch leaf-feeding beetles (Agelastica alni and Phyllobius spp) and how it affects the relative growth rate of the lepidopteran larvae. The results indicated that transgenic lignin did not have significant effects on the feeding preferences of the insect herbivores. No differences were found in the growth performance of lepidopteran larvae feeding on transgenic or control leaves.

The results are important for environmental assessments regarding transgenic forest trees and moreover, in political decision-making on the role of transgenic forest trees in forest economy based on sustainable development. The study was a joint project between the University of Oulu and Metla.

Additional information: www.metla.fi/hanke/7150/index-en.htm

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