Bombardier beetles repel invasive bullfrogs.

Area of Science:

• Ecology
• Evolutionary Biology
• Chemical Ecology

Background:

• Invasive predators pose significant threats to native ecosystems.
• Native species may possess pre-existing or evolved defenses against invasive species.
• The American bullfrog (Lithobates catesbeianus) is an invasive predator impacting native fauna.

Purpose of the Study:

• To investigate the effectiveness of the bombardier beetle's chemical defense against invasive American bullfrogs.
• To determine if the bombardier beetle (Pheropsophus occipitalis jessoensis) can deter predation by the American bullfrog.
• To assess the role of chemical "bombing" in the defense of native insects against invasive predators.

Main Methods:

• Laboratory experiments exposing juvenile American bullfrogs to adult native bombardier beetles.
• Observation of bullfrog behavioral responses, including rejection, attack cessation, and ingestion.
• Comparison of responses to normal beetles versus beetles with disabled chemical defense mechanisms.

Main Results:

• Over 96% of bullfrogs rejected bombardier beetles before ingestion.
• 88.9% of bullfrogs ceased attacks after being "bombed" by the beetles.
• Bullfrogs successfully consumed 77.8% of beetles unable to discharge chemicals, indicating the defense's importance.

Conclusions:

• The chemical "bombing" defense of Pheropsophus occipitalis jessoensis is crucial for repelling invasive American bullfrogs.
• Native bombardier beetles possess a strong defense mechanism against this invasive predator.
• Despite the bullfrog's predatory impact, native insect defenses can be effective.