Forests (2022) 13 (4 - 537)

Sigrid Netherer, Martin Schebeck, Giuseppe Morgante, Verena Rentsch and Thomas Kirisits (2022)
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
Forests 13 (4 - 537)
Abstract: 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.
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Database assignments for author(s): Sigrid Netherer, Martin Schebeck, Thomas Kirisits

Research topic(s) for pests/diseases/weeds:
population dynamics/ epidemiology
general biology - morphology - evolution

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Ips typographus	Spruce (Picea)	Austria