How can improper mosquito larvicide application affect water quality and aquatic habitats?

• A. Over-application has no effect on non-target aquatic organisms.
• B. Over-application can harm non-target aquatic organisms; follow label rates, avoid sensitive habitats, and use targeted applications.
• C. Using any amount of larvicide always reduces non-target organisms and is dangerous.
• D. Larvicide applications have no impact on water quality.

Answer: (B)

Overuse or mis-timing of mosquito larvicide applications can harm non-target aquatic organisms and degrade water quality. Exceeding labeled rates or applying inappropriately can leave residues in water that affect aquatic invertebrates, fish, and amphibians, disrupting food webs and reducing biodiversity in the habitat. Following label directions keeps concentrations within what has been tested as safe for non-target species. Targeted applications—treating only known mosquito breeding sites and avoiding sensitive habitats like streams, springs, wetlands, or areas with endangered species—minimize unnecessary exposure and protect ecological health. Pairing chemical control with non-chemical approaches, such as eliminating standing water and using selective biological controls, further reduces ecological risk. While some larvicides (including certain microbial products) can be relatively selective, they can still impact non-target organisms if misused, so responsible application helps preserve water quality and aquatic habitat integrity.