Document: ERK-3-23-8

Birch leaves as moving targets for herbivores.

HAUKIOJA, E.*

University of Turku, FIN-20014 Turku, FINLAND ¹

Abstract:
Life cycles of folivorous insects typically last for one year, while their woody hosts may live for hundreds of years. Why the short lived pests have not been able to completely overcome host resistance presumably relates to phenotypic variability of the host. I studied the role of phenological changes in birch leaf quality for its most destructive folivore, the geometrid Epirrita autumnata. In flushing birch leaves, concentrations of hydrolyzable tannins, especially of gallotannins, best predict the performance of E. autumnata. Gallotannin concentrations rapidly decline during leaf growth, while condensed tannins go up. In maturing leaves, soluble proanthocyanidins best correlate with larval performance. In mature leaves, leaf toughness and shortage of nitrogen were the limiting traits. These rapid and profound shifts in the relevant resistance mechanisms of leaves per se during the larval period may deter adaptation of the herbivore to the host, particularly if the successive resistance traits cannot be handled by the same mechanisms. This is indicated by zero correlations between performance of young larvae on young leaves and of older larvae on more mature leaves of the same trees. That E. autumnata seems to be unable to optimally handle the successive resistance mechanims of the host offers a novel explanation why the short lived, potentially very destructive insect has not been able to breach the resistance of its long lived host.

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This abstract is being presented at: 3:45 PM in session:
Symposium # 23: Why Variation is Not Just Noise: The Influence of Variability on Plant-Herbivore and Plant-Pathogen Interactions.