Which statement about Bti safety and non-target risk is most accurate when used as labeled?

• A. Bti is highly toxic to vertebrates.
• B. Bti leaves a long-lasting residue in water.
• C. Bti has significant non-target risks in all uses.
• D. Bti is a microbial larvicide with minimal risk to non-target organisms when used as labeled.

Answer: (D)

Bti is a microbial larvicide that is highly specific to mosquito and certain fly larvae, and when applied according to the label it carries minimal risk to non-target organisms. Its toxins (Cry and Cyt proteins) are activated in the gut of susceptible Dipteran larvae, causing their death, while vertebrates and most non-target aquatic organisms are not affected at labeled use rates. It does not persist long in the environment; it degrades with exposure to light, temperature, and microbial action, and it does not accumulate in water or organisms. Because of this specificity and rapid breakdown, the risk to non-targets is minimal when Bti is used as directed.