Do water-limiting conditions predispose Norway spruce to bark beetle attack?

Area of Science:

• Forestry
• Ecology
• Entomology

Background:

• Norway spruce (Picea abies) susceptibility to Eurasian spruce bark beetle (Ips typographus) infestations is thought to increase under drought conditions.
• Empirical evidence supporting this hypothesis is limited.

Purpose of the Study:

• To investigate the impact of experimentally induced drought on Norway spruce water status and resin flow.
• To determine how physiological stress influences host acceptance and resistance to bark beetle attack.

Main Methods:

• Rain-out shelters were used to create severe and moderate drought conditions in experimental plots.
• Eighteen Norway spruce trees were divided among drought-treated and control plots.
• A novel 'attack box' method was employed to control experimental bark beetle infestations.

Main Results:

• Drought treatments affected the success and defense rates of bark beetle attacks.
• Individual tree stress levels, indicated by twig water potential and resin exudation, were primary drivers of infestation susceptibility.
• Decreasing water potential and resin flow correlated with reduced tree defense capabilities.

Conclusions:

• Water-limiting conditions demonstrably impair Norway spruce resistance to Ips typographus attack.
• Extreme drought stress may lead to reduced host acceptance by Ips typographus, as evidenced by negative pre-dawn twig water potentials.