Cost-Effective Monitoring of Spruce Budworm Larvae

Area of Science:

• Forest entomology
• Insect pest management
• Forestry science

Background:

• Spruce budworm (Choristoneura fumiferana) is a major defoliator of balsam fir (Abies balsamea) in eastern Canada and the northeastern U.S.A.
• A significant outbreak is ongoing in Québec, with 10.5 million hectares defoliated in 2023.
• Current management relies on the Forest Protection Strategy (FPS), using microbial insecticides to control larvae and prevent tree mortality.

Purpose of the Study:

• To propose a cost-effective monitoring approach for spruce budworm populations.
• To optimize the Forest Protection Strategy (FPS) by reducing monitoring costs.
• To maintain effective management of spruce budworm outbreaks while achieving financial savings.

Main Methods:

• Monitoring overwintering second instars (L2) at approximately 600 sampling points across Québec.
• Utilizing the Forest Protection Strategy (FPS) threshold (T_FPS) of 20 L2/branch to guide treatment decisions.
• Analyzing budworm abundance decline with distance from aerial defoliation to identify areas for reduced sampling frequency.

Main Results:

• Spruce budworm populations decline rapidly with distance from aerial defoliation, rarely exceeding the T_FPS threshold beyond 15 km.
• A proposed monitoring strategy involves sampling forest blocks outside the core FPS range every second year instead of annually.
• This revised monitoring approach offers potential annual savings of CAD 40,000.

Conclusions:

• The spatial distribution of spruce budworm populations allows for a reduced monitoring frequency in less affected areas.
• Implementing a biennial sampling strategy outside the core FPS range is a cost-effective method for managing spruce budworm.
• This optimized monitoring approach can lead to significant financial economies without compromising outbreak management effectiveness.