Abstract

Willows (Salix cinerea) exposed to grazing by adult leaf beetles (Phratora vulgatissima) produce new leaves with a higher density of trichomes. The higher trichome density affects the next generation of beetle larvae negatively, through a more dispersed feeding, resulting in a lower total food intake and slower growth. The third trophic level, i.e. generalistic heteropteran predators, does not seem to be affected by trichome density, at least not when measured in number of leaf beetle eggs consumed per time unit on willow shoots. This means that we have an inducible plant trait that increase plant resistance against a known pest insect but that has no negative effects on important natural enemies. Inducible resistance thus has the potential of being used as part of a management method of willow leaf beetles. However, the willow species most often used in commercial willow plantations (to produce biomass), S. viminalis, does not respond to beetle grazing with increased leaf hairiness or any other detectable induced response. In addition, quantitive measurements of the costs associated with the induced increase in leaf hairiness will be presented. Preliminary results indicate that costs can only be detected when willows are grown under competitive, and more natural, conditions but not when grown under more optimal (i.e. no competition for light) conditions

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Conference

SIP 12

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