Zur Phänologie des Buchenprachtkäfers Agrilus viridis L. (Col., Buprestidae) in Süddeutschland

Initiated by a severe outbreak of the beech splendour beetle (Agrilus viridis L.) in Hungary and the increasing importance of beech (Fagus sylvatica L.) for managed forests in Central Europe, we studied the phenology of A. viridis. From 2010 to 2012 we investigated swarming, activity density and development time of A. viridis in eight mature beech stands located in prominent beech growing areas of Bavaria (southern Germany) (Fig. 1). Swarming set on in the second half of May and lasted until begin (2011, 2012) and end (2010) of September, respectively (Fig. 3A). Heat sum calculated as DDTmax15 (sum of daily maximum crown temperature minus 15° C) synchronized the flight activity of the beetles very well (Fig. 3B) and significantly better than the Julian date (Fig. 4). The relative low number of trapped beetles (384 in three years) indicated a latent population density during the study period. Swarming beetles correlated significantly with mean maximum temperatures in the beech crowns (Fig. 5). In latency, the beetles showed only an unremarkable dispersal activity and seemed to remain for more than one generation in an individual beech crown, when they initially achieved to colonize some branches. The dieback of infested branches enhances the temperature within the crown and thus, the thermophilic beetle itself improves the habitat for further generations. Oviposition on trap trees peaked 3 to 4 weeks after felling (Tab. 1). The number of egg clusters deposited on trap trees ranged from 28 to 159 per tree (mean 81). The percentage of egg clusters with entrance holes of 1^st instar larvae was 52,7%. Based on these clusters the mean number of eggs per cluster was 5.32. In the field, mean development time ranged between 352 and 403 days (Tab. 2). Thus, A. viridis must be expected to occur in overlapping generations with one and two-year development.