How are degree-days used to time mosquito control operations, and what temperature threshold is commonly used to activate development?

• A. Degree-days estimate progression from immature stages to emergence; a common threshold is about 10°C (50°F) for many species.
• B. They measure rainfall; threshold 25°C.
• C. They track wind speed; threshold 0°C.
• D. They are not used; threshold 20°C.

Answer: (A)

Degree-days track how much heat mosquitoes experience so you can predict when their immature stages will progress to the next life stage and emerge as adults. By summing the daily heat above a baseline threshold, you get an estimate of timing for development milestones. This allows crews to schedule control actions—like larviciding before or during vulnerable larval stages or timing adult control around expected emergence—when they’re most effective and cost-efficient.

The commonly used threshold is about 10°C (50°F) for many mosquito species. Temperatures below this limit don’t drive development much, while above it development proceeds and degree-days accumulate more quickly. That’s why 10°C is a standard basis for activating development in degree-day models.

These concepts don’t involve rainfall or wind, and degree-days are indeed used in mosquito management to time operations.