Bacillus sphaericus (Bsph) is noted for long residual effects and activity against Culex and Anopheline larvae, with potential for resistance in some species. Which statement is true?

• A. Bsph has short residual effects and is only effective on Aedes larvae.
• B. Bsph has long residual effects and can face resistance in some species.
• C. Bsph is used primarily for adult mosquito control.
• D. Bsph is a chemical insecticide with broad non-target effects.

Answer: (B)

Bacillus sphaericus is a biological larvicide that persists in water for an extended period because its spores and toxins remain active in the larval habitat. It specifically targets larvae of Culex and Anopheles mosquitoes, rather than adult mosquitoes, and it is not a chemical insecticide. Because the toxin acts by binding to receptors in the larvae’s gut, some mosquito populations can evolve reduced susceptibility, leading to resistance in certain species. So the statement that matches these points—long residual effects, activity against Culex and Anopheline larvae, and potential for resistance in some species—is true.