Defensive Effect of Surface Flavonoid Aglycones of Betula pubescens Leaves Against First Instar Epirrita autumnata Larvae

Abstract:

The surface of birch leaves contains glandular trichomes that secrete exudates containing flavonoid aglycones. We investigated the biological activities of white birch (Betula pubescens) leaf surface exudates against larvae of the autumnal moth, Epirrita autumnata, a common insect pest of birch. We found that tree-specific mortality (up to 100%) of first instar larvae correlated strongly with the tree-specific contents of surface flavonoid aglycones (r_s=0.905) in emerging leaves. We also found that first instars clearly preferred birch buds from which surface exudates had been removed. In addition, the duration of the first instar was shortened by 29%, and the weights and relative growth rates of first instars improved by 8% and 52%, respectively, as a result of removal of the exudates from their leaf diet. The correlation of tree-specific foliar contents of flavonoid aglycones, especially 5-hydroxy-4',7-dimethoxyflavanone, with changes in larval performance, suggests that flavonoid aglycones are responsible for the changes observed in first instar larval performance. The results show that chemical characteristics of birch leaves are effective against neonate E. autumnata larvae. However, the removal of leaf surface exudates from fully expanded leaves did not affect the leaf acceptance for the voracious fifth instars. This is probably a result of reduction in contents of flavonoid aglycones compared to those of emerging leaves.

Keywords: Flavonoid aglycones; biological activity; birch; Betula pubescens; Epirrita autumnata; first instar

Document Type: Research article

DOI: 10.1023/B:JOEC.0000048787.34388.dd

Affiliations: 1: Laboratory of Environmental Chemistry, Department of Chemistry, University of Turku, FI-20014 Turku, Finland;, Email: makahe@utu.fi 2: Laboratory of Environmental Chemistry, Department of Chemistry, University of Turku, FI-20014 Turku, Finland 3: Section of Ecology, Department of Biology, University of Turku, FI-20014, Turku, Finland 4: Laboratory of Environmental Chemistry, Department of Chemistry, University of Turku, FI-20014 Turku, Finland. Section of Ecology, Department of Biology, University of Turku, FI-20014, Turku, Finland 5: Structural Chemistry Group, Department of Chemistry, University of Turku, FI-20014 Turku, Finland 6: Laboratory of Environmental Chemistry, Department of Chemistry, University of Turku, FI-20014 Turku, Finland. Structural Chemistry Group, Department of Chemistry, University of Turku, FI-20014 Turku, Finland