Drought increases Norway spruce susceptibility to the Eurasian spruce bark beetle and its associated fungi.

Drought affects the complex interactions between Norway spruce, the bark beetle Ips typographus and associated microorganisms. We investigated the interplay of tree water status, defense and carbohydrate reserves with the incidence of bark beetle attack and infection of associated fungi in mature spruce trees. We installed roofs to induce a 2-yr moderate drought in a managed spruce stand to examine a maximum of 10 roof and 10 control trees for resin flow (RF), predawn twig water potentials, terpene, phenolic and carbohydrate bark concentrations, and bark beetle borings in field bioassays before and after inoculation with Endoconidiophora polonica and Grosmannia penicillata. Drought-stressed trees showed more attacks and significantly longer fungal lesions than controls, but maintained terpene resin defenses at predrought levels. Reduced RF and lower mono- and diterpene, but not phenolic concentrations were linked with increased host selection. Bark beetle attack and fungi stimulated chemical defenses, yet G. penicillata reduced phenolic and carbohydrate contents. Chemical defenses did not decrease under mild, prolonged drought in our simulated small-scale biotic infestations. However, during natural mass attacks, reductions in carbon fixation under drought, in combination with fungal consumption of carbohydrates, may deplete tree defenses and facilitate colonization by I. typographus.

Addressing a century-old hypothesis - do pioneer beetles of Ips typographus use volatile cues to find suitable host trees?

Global warming and more frequent climate extremes have caused bark beetle outbreaks of unprecedented scale of these insects in many conifer forests world-wide. Conifers that have been weakened by drought and heat or damaged by storms are highly susceptible to bark beetle infestation. A large proportion of trees with impaired defences provides good conditions for beetle population build-up of beetles, but mechanisms driving host search of pioneer beetles are still uncertain in several species, including the Eurasian spruce bark beetle Ips typographus. Despite a two-century-long history of bark beetle research, we still lack a sufficient understanding of interactions between I. typographus and its host Norway spruce (Picea abies) to forecast future disturbance regimes and forest dynamics. Depending on the scale (habitat or patch) and beetle population state (endemic or epidemic), host selection is likely driven by a combination of pre and postlanding cues, including visual selection or olfactory detection (kairomones). Here, we discuss primary attraction mechanisms and how volatile emission profiles of Norway spruce may provide cues on tree vitality and suitability for attacks by I. typographus, in particular during the endemic phase. We identify several crucial knowledge gaps and provide a research agenda addressing the experimental challenges of such investigations.

Revision of the genus Laophontodes T. Scott (Copepoda, Harpacticoida, Ancorabolidae), including the description of a new species and a key to species.

The description of Laophontodes volkerlehmanskii sp. nov. (Copepoda, Harpacticoida, Laophontodinae Lang) from the deep sea of the Kairei Field, western Indian Ocean, prompted the examination of the phylogenetic status of Laophontodes T. Scott and the relationships within the genus. The allocation of L. volkerlehmanskii sp. nov. to Laophontodes based on diagnostic characters was relatively straightforward, yet phylogenetic analysis of the genus considering 39 morphological characters detected not a single autapomorphy. This indicates that Laophontodes, which seems to form a monophylum with Ancorabolina George and Bicorniphontodes George, Glatzel & Schröder, actually represents the stem-lineage, retaining the characters of the common ancestor without having developed unique derived morphological characters. Most of the 13 known species of Laophontodes can be characterised by distinct apomorphies. However, phylogenetic comparison highlights some uncertainties due to the apparent heterogeneous distribution of some derived characters across the species, the weakness of other features, and the fragmentary and inadequate description of several species, which, in combination with the unavailability of type material, prevents a detailed comparison of several phylogenetically relevant characters. Thus, the analysis presented here provides a further step towards understanding the systematic relationships of and within Laophontodes, rather than a conclusive answer. Nonetheless, a detailed character discussion and a key to species are given.