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

Abstract

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 (1962-2007), precipitation (1922-2007), and the damage caused by I. typographus (1993-2007). In addition, data from pheromone-baited traps (1996-2005) provided information on the main periods of flight activity of I. typographus. From 1922 to 2007, precipitation during March-July has decreased approximately 200 mm (-22%), whereas since 1962-2007, mean temperatures during March-July increased approximately 2 degrees C (+13%). Damage caused by I. typographus was inversely correlated with March-July precipitation from the previous year but not correlated with temperature. Increases in spring temperature did not affect the development timing of the first generation, but only changed its onset. Earlier swarming of both overwintering beetles and first-generation offspring ( approximately 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.

Composition and Elevation of Spruce Forests Affect Susceptibility to Bark Beetle Attacks: Implications for Forest Management

“…Recent studies from northern [13] and central Europe [3] report that the availability of breeding substrates and the ability of I. typographus to colonize spruce trees growing in suboptimal conditions are the main abiotic factors triggering I. typographus outbreaks. A number of environmental factors may indirectly affect the population dynamics of I. typographus, acting on the susceptibility of the host trees through severe climate events, e.g., drought, heat waves, wind or snow storms, occurring in sites unsuitable for spruce growing [11,17,19]. In this respect, the warm summer temperature recorded in the last few years in southern Europe [45] became one of the main factors affecting the general health conditions of spruce forests [46].…”

“…In this respect, the warm summer temperature recorded in the last few years in southern Europe [45] became one of the main factors affecting the general health conditions of spruce forests [46]. Long, warm and dry summers may enhance tree susceptibility to forest pests [11,17,19], and I. typographus outbreaks were often associated with these events [11]. In the same region where this study was carried out, Marini et al [19] found an altitudinal distribution of I. typographus damage correlated with summer temperature and insect outbreak dynamics.…”

“…Recent studies carried out on the south-eastern Alps show, for instance, a mean damage per hectare about seven times higher in spruce forests growing in sites warmer than those within the natural climatic range of spruce [19]. Moreover, the intensity and altitudinal distribution of the insect outbreaks were affected by dry summers, which were related to an increase of the mean damage [17] and an upward shift of the altitudinal outbreak range [19]. A preliminary investigation carried out in the same region reported that silvicultural practices may substantially modify the susceptibility of spruce trees to I. typographus infestations [20].…”

“…In the last few years, the spruce bark beetle, Ips typographus (L.), one of the most destructive insects infesting spruce forests (Picea abies Karsten), caused serious damage almost everywhere in Europe [3,[11][12][13]. Severe damage was also recorded in spruce forests growing on the Southern Alps [14][15][16][17][18][19]. Large I. typographus outbreaks were observed mainly in sites with environmental conditions not fully suitable for spruce.…”

Seasonal flight patterns of Ips typographus in southern Sweden and thermal sums required for emergence

“…flight activity between early May and mid-August (Harding and Ravn, 1985), or the flight period in Central Europe which is even longer, i.e. between April and September (Faccoli andStergulc, 2004, Baier et al, 2007). Such an extended flight period has also been recorded further north, (i.e.…”