Vitality loss of European beech (Fagus sylvatica L.) and infestation by the European beech splendour beetle (Agrilus viridis L., Buprestidae, Coleoptera)

Despite its dominance in Central Europe, beech cultivation is not without risks, because drought periods and direct solar radiation of the stem are suspected of causing branch dieback, sunburn and predisposition to attack by the European beech splendour beetle Agrilus viridis. Outbreaks of this beetle occurred in Germany in the early 1950s and in Hungary between 2003 and 2006 following severe precipitation deficiencies and extraordinary high temperatures. Leaf loss and an unusual accumulation of dead branches at the top of the crown of beech trees prompted us to initiate in 2010 a three-year study to investigate whether and to what extent A. viridis infestations are involved in this damage pattern. In eight differently damaged beech stands in Bavaria (south-eastern Germany) we measured the prevalence of A. viridis with flight interception traps in relation to the vitality status of beech, checked the oviposition behaviour of females on trap trees, and investigated the infestation frequency of beech trees depending on stand structure. The prevalence of A. viridis was significantly enhanced in sample plots with more heavily damaged beech trees. At lying trap trees, females preferred parts of the bark for oviposition which had been exposed to south or west when the trees had been standing. Particularly, trees in open stands, distant to neighbours in the south and west as well as damaged by sunburn are predisposed to attack by A. viridis. It was proved that survival of A. viridis occurred in branches at the top of live beech trees from where outbreak situations may be initiated due to climatic conditions like drought and/or extreme temperatures. Prevention of A. viridis infestation consists of avoiding sudden exposure to intense solar radiation of the beech trunk by silvicultural measures.