Effects of Vegetation Disturbances on Insect Biological Control of Tansy Ragwort, Senecio Jacobaea

Area of Science:

• Ecology
• Biological Control
• Invasive Species Management

Background:

• Tansy ragwort (Senecio jacobaea) is a problematic pasture weed.
• Understanding weed outbreak triggers and biological control efficacy is crucial for effective management.
• Localized disturbance and natural enemies play key roles in weed population dynamics.

Purpose of the Study:

• To investigate the roles of buried seed and localized disturbance in activating tansy ragwort outbreaks.
• To evaluate the effectiveness of the cinnabar moth (Tyria jacobaeae) and the ragwort flea beetle (Longitarsus jacobaeae) in controlling tansy ragwort.
• To assess how disturbance and natural enemies influence weed population increase and spread.

Main Methods:

• A 5-year field experiment was conducted on the Oregon coast.
• A randomized-block design included treatments for disturbance (Tilled, Clipped, Unaltered), cinnabar moth (Exposed, Protected), and flea beetle (Exposed, Protected).
• Ragwort abundance was measured via density, cover, and biomass; natural enemy impact was assessed through survival and fecundity.

Main Results:

• Disturbance significantly increased tansy ragwort abundance, with tilling having a greater effect than clipping.
• The ragwort flea beetle rapidly reduced weed survival and abundance.
• The cinnabar moth reduced fecundity but did not significantly impact ragwort cover or biomass.

Conclusions:

• Tansy ragwort populations are primarily limited by microsite availability for establishment, not seed availability.
• The ragwort flea beetle is the key natural enemy regulating tansy ragwort abundance.
• Biological control effectiveness depends on the specific natural enemy and interaction with environmental disturbances.