The pathogen causing Dutch elm disease makes host trees attract insect vectors.

Area of Science:

• Plant pathology
• Chemical ecology
• Forest entomology

Background:

• Dutch elm disease is a destructive fungal disease affecting American elm (Ulmus americana) populations.
• The disease is primarily transmitted by the native elm bark beetle (Hylurgopinus rufipes).
• Understanding insect-pathogen-host interactions is crucial for disease management.

Purpose of the Study:

• To identify semiochemicals emitted by diseased American elms that attract Hylurgopinus rufipes.
• To investigate the role of fungal inoculation in altering host tree volatile emissions.
• To elucidate the mechanism by which Ophiostoma novo-ulmi manipulates its vector for enhanced transmission.

Main Methods:

• Gas chromatography-electroantennographic detection (GC-EAD) was used to identify beetle-attracting volatiles from diseased elms.
• Volatile organic compounds (VOCs) emitted by healthy and Ophiostoma novo-ulmi-inoculated elm trees were analyzed.
• Bioassays were conducted to assess the synergistic attractiveness of identified semiochemicals to H. rufipes.

Main Results:

• Four semiochemicals, including (-)-beta-pinene, (-)-alpha-cubebene, (+)-spiroaxa-5,7-diene, and (+)-delta-cadinene, were identified as synergistic attractants for H. rufipes.
• Sesquiterpene emission from American elm trees was significantly upregulated following inoculation with Ophiostoma novo-ulmi.
• The identified semiochemical blend demonstrated a synergistic effect, enhancing beetle attraction.

Conclusions:

• Ophiostoma novo-ulmi manipulates American elm trees to emit specific semiochemicals that attract Hylurgopinus rufipes.
• This fungal manipulation enhances the apparency of diseased trees to foraging beetles.
• The strategy increases the likelihood of pathogen transmission to new, susceptible elm hosts, facilitating disease spread.