Monarch Butterfly (Danaus plexippus) Life-Stage Risks from Foliar and Seed-Treatment Insecticides

Area of Science:

• Environmental Toxicology
• Ecology
• Entomology

Background:

• Monarch butterfly (Danaus plexippus) populations in North America require milkweed and nectar plants in agricultural landscapes.
• Pesticides, including seed treatments and foliar sprays, are used in these landscapes, posing potential risks to monarchs.
• Assessing insecticide risks to monarch life stages is crucial for effective habitat conservation.

Purpose of the Study:

• To evaluate the toxicity of six common insecticides to various monarch butterfly life stages.
• To compare insecticide toxicity data with estimated environmental exposure levels.
• To inform habitat conservation strategies for monarch butterflies in agricultural regions.

Main Methods:

• Conducted chronic and acute dietary toxicity studies on monarch larvae and adults.
• Performed acute topical bioassays on monarch eggs, pupae, and adults.
• Tested six insecticides: beta-cyfluthrin, chlorantraniliprole, chlorpyrifos, imidacloprid, clothianidin, and thiamethoxam.

Main Results:

• Chronic larval toxicity varied, with chlorantraniliprole (1.6 × 10⁻³ μg/g) being most toxic and chlorpyrifos (5.3 μg/g) least toxic.
• Neonicotinoids caused significant pupal ecdysis arrest; chlorantraniliprole and beta-cyfluthrin were generally most toxic across life stages.
• Aerial insecticide application predicted high larval and egg mortality, while neonicotinoid seed treatments showed minimal impact.

Conclusions:

• Insecticide toxicity to monarchs varies significantly by chemical class and life stage.
• Habitat establishment near agricultural fields may not negatively impact adult monarch recruitment if insecticide risks are managed.
• Conservation efforts should consider insecticide use patterns and monarch exposure pathways in agricultural landscapes.