Effect of Weather on Ips typographus (Coleoptera Curculionidae) Phenology, Voltinism, and Associated Spruce Mortality in the Southeastern Alps

Summer drought associated with high temperatures recorded in the last few years has given rise to outbreaks of bark beetles developing in weakened host trees. The aim of this study was to investigate the possible weather effect on the biology of and damage caused by Ips typographus L. in the southeastern Alps. The study was carried out recording temperature (1962Ð2007), precipitation (1922Ð2007), and the damage caused by I. typographus (1993Ð2007). In addition, data from pheromone- baited traps (1996Ð2005) provided information on the main periods of ßight activity of I. typographus. From 1922 to 2007, precipitation during MarchÐJuly has decreased 200 mm (22%), whereas since 1962Ð2007, mean temperatures during MarchÐJuly increased 2C (13%). Damage caused by I. typographus was inversely correlated with MarchÐJuly precipitation from the previous year but not correlated with temperature. Increases in spring temperature did not affect the development timing of the Þrst generation, but only changed its onset. Earlier swarming of both overwintering beetles and Þrst-generation offspring (20 d sooner over 10 yr), and the early start of the second generation permitted more complete development of the second brood. Voltinism in this species is discussed in relation to thermal and photoperiodic thresholds, indicating that the occurrence of a third generation is limited by the summer photoperiod rather than by temperature. In conclusion, results suggest that spring drought increases damage caused by I. typographus in the following year, whereas warmer spring affects insect phenology.