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Conference abstract2008

Conservation biological control via unharvested enemy refugia: coppicing willows, leaf beetles and predatory bugs

Björkman, Christer


Introduction: Disturbances are common in natural systems and may affect important ecosystem processes (e.g. predation and hence biological control). If the perturbations, e.g. harvesting, are predictable they can be used to test ecological theories in large-scale field experiments. Methods: Densities of leaf beetles (prey) and mirid bugs (predators) were compared in (i) coppicing willow plantations different years after harvest and (ii) in plantations with and without unharvested parts, expected to function as enemy refugia. Results: Harvesting disrupts the biological control of leaf beetles in short rotation coppice willow plantations. The reason is that the main natural enemies (mirid bugs) are removed at harvesting, taking place in winter. The reason for this is that the bugs overwinter as eggs oviposited in willow tissue and we show that the density of mirid eggs increase with time after harvesting. The leaf beetles, overwintering outside the plantations, can thereby return to an enemy-free space in spring. We hypothesized that one way to conserve biological control would be to leave unharvested willows, functioning as enemy refugia. The results from a field experiment showed that (1) enemy densities and (2) predation pressure (but to a lower extent) was higher within than outside refugia, and (3) both leaf beetles and mirid bugs were positively affected by refugia on whole stand level. Conclusions: Leaving unharvested refugia may affect the pest more positively than the predators. Our results illustrate the need to consider scale and basic biological knowledge before launching simple solutions to complex problems

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    UKÄ Subject classification

    Agricultural Science
    Environmental Sciences related to Agriculture and Land-use
    Renewable Bioenergy Research

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