The Eurasian spruce bark beetle: the role of climate.

Abstract The Eurasian spruce bark beetle is one of the major forest pests in Europe, capable of mass attacking and killing Norway spruce over extensive areas during outbreaks. Here, we review various aspects of its biology in relation to climatic variables. The aim of this review was to make predictions about the potential consequences of climate change on the propensity for outbreaks across European forests. More frequent extreme winds and drier and warmer summer climate may trigger both population growth and the susceptibility of spruce stands to attack. Breeding material provided by large windfall events increase the beetle population rapidly to a level capable of killing living trees through mass attack. Such epidemics may proceed until the susceptible spruces are exhausted, or when other extrinsic conditions stop the bark beetles from further colonization. At the southern margin of the spruce distribution in Europe, lower than average precipitation seems generally to favour infestations. In central and Western Europe, even-aged plantations outside the natural range of Norway spruce are highly susceptible to disturbance events such as windthrow and bark beetle attacks. A warmer climate is expected to give a northern expansion of the area experiencing two generations per year in Europe. There have been few bark beetle outbreaks in the extensive areas of spruce forest in Finland and the northern part of Scandinavia, but increasing bark beetle populations and infestations have been observed during warm years in the last decade. The northern part of Europe may be subject to huge outbreaks if a warmer climate increases the population sizes of the Eurasian spruce bark beetle.</p

The Eurasian spruce bark beetle: The role of climate

The Eurasian spruce bark beetle is one of the major forest pests in Europe, capable of mass attacking and killing Norway spruce over extensive areas during outbreaks. Here, we review various aspects of its biology in relation to climatic variables. The aim of this review was to make predictions about the potential consequences of climate change on the propensity for outbreaks across European forests. More frequent extreme winds and drier and warmer summer climate may trigger both population growth and the susceptibility of spruce stands to attack. Breeding material provided by large windfall events increase the beetle population rapidly to a level capable of killing living trees through mass attack. Such epidemics may proceed until the susceptible spruces are exhausted, or when other extrinsic conditions stop the bark beetles from further colonization. At the southern margin of the spruce distribution in Europe, lower than average precipitation seems generally to favour infestations. In central and Western Europe, even-aged plantations outside the natural range of Norway spruce are highly susceptible to disturbance events such as windthrow and bark beetle attacks. A warmer climate is expected to give a northern expansion of the area experiencing two generations per year in Europe. There have been few bark beetle outbreaks in the extensive areas of spruce forest in Finland and the northern part of Scandinavia, but increasing bark beetle populations and infestations have been observed during warm years in the last decade. The northern part of Europe may be subject to huge outbreaks if a warmer climate increases the population sizes of the Eurasian spruce bark beetle

European Spruce Bark Beetle, Ips typographus (L.) Males Are Attracted to Bark Cores of Drought‐Stressed Norway Spruce Trees with Impaired Defenses in Petri Dish Choice Experiments

The European spruce bark beetle, Ips typographus (L.), is a major pest of Norway spruce. During outbreaks, the beetles can colonize moderately stressed trees via mass attacks mediated by aggregation pheromones, while at endemic population levels, beetles infest trees with impaired defenses. I. typographus introduces ophiostomatoid fungi into the phloem, which can support host colonization. Low-density fungal infections are locally contained by hypersensitive wound reactions; larger necrotic lesions indicate lower tree resistance. Here, we made links between drought stress, susceptibility to fungal infections, and the attractiveness of spruce for host-searching I. typographus males. We sampled bark cores from roofed, non-roofed and untreated control trees of a rainfall exclusion field site. Drought stress was assessed using pre-dawn twig water potentials, and tree defenses were assessed using inoculations with Grosmannia penicillata. Subsequently, we performed Petri dish arena choice tests in the lab, where male beetles could choose between the bark samples of differentially stressed trees. We found that the attractiveness of bark cores increased with drought stress and the extent of hypersensitive wound reactions to fungal infection. Furthermore, beetles stayed longer in those Petri dish sections with the sample of their final choice. The bioassays provide evidence for the primary attraction of male I. typographus to tissues of Norway spruce and preference of beetles for stressed trees

Expansion of geographic range in the pine processionary moth caused by increased winter temperatures

Global warming is predicted to cause distributional changes in organisms whose geographic ranges are, at least in part, controlled by temperature. We report a recent latitudinal and altitudinal expansion of the pine processionary moth, Thaumetopoea pityocampa, whose larvae build silk nests and feed on pine foliage in the winter. In north-central France (Paris Basin), its range boundary has shifted by 87 km northwards between (1972 andto 2004); in northern Italy (Venosta/VinschgauAlps), the an altitudinal shift of corresponds to 110-230 m upwards occurred between( 1975 to and 2004), depending on the slope aspect. By experimentally linking winter temperature, feeding activity, and survival of T. pityocampa larvae, wWe attribute the expansions to increased winter survival due to the effects of the a warming trend in over the past three decades, by experimentally linking winter temperature, feeding activity and survival of T. pityocampa larvae. In the laboratory, we determined the minimum nest and night air temperatures required for larval feeding, and developed a simple mechanistic model based on these temperature thresholds. We tested the model in a translocation experiment that employed natural temperature gradients as spatial analogues for global warming. In all transects, we transferred colonies of T. pityocampa larvae to sites within zones of historical distribution, recent distribution, and outside the present range (northern- or uppermost). We monitored air and nest temperature, incoming solar radiation (insolation), and larval phenologyphenology, feeding activity, and survival. Early-season temperature effects on phenology were evident, with delayed development of colonies in the more extreme (colder) sites showing ed development. In the coldest months, our predictive model was consistent with the observed patterns of feeding activity: feeding was progressively reduced with increasing latitude or elevation, as predicted by the lower number of hours when the feeding threshold was reached, and negatively affected final survival. Insolation raised nest temperature and increased feeding activity oOn the south-facing slope but not the north aspect, insolation raised nest temperature, thereby increasing feeding activity. Prolonged temperature drops below the feeding thresholds occurred at all sites during the coldest months, leading to starvation and partial mortality. Nonetheless, even the more most extreme (colder) sites still allowed some feeding, and, consequently, up to 20% colony survival and successful pupation. Given that the present distribution of the oligophagous T. pityocampa is not constrained by the distribution of its actual or potential hosts, and that warmer winters will cause the number of hours of feeding to increase and the probability of the lower lethal temperature to decrease, we expect the trend of improved survival in previously prohibitive environments to continue, causing further latitudinal and altitudinal expansion. This work highlights the need to develop temperature-based predictive models for future range shifts of winter-limited species, with potential applications in management