Mosquitoes are highly sensitive to environmental conditions, with temperature being a critical factor for their activity, development, and survival. As cold-blooded insects, their internal body temperature directly reflects their surroundings, influencing every biological process. Understanding how temperature affects mosquitoes is important for managing their populations and mitigating the risks of mosquito-borne diseases.
How Cold Affects Mosquito Survival
Mosquitoes become less active when temperatures fall below 10°C (50°F), as their metabolic processes slow. At these lower temperatures, female mosquitoes are less likely to seek blood meals, and larval development is interrupted. Most adult mosquitoes perish when temperatures drop below 0°C (32°F) due to freezing of internal fluids.
Some species employ survival strategies like diapause, a dormant state similar to hibernation, where metabolic activity decreases. This allows adult females or eggs to survive months of cold weather. For instance, Aedes albopictus eggs can enter diapause, and some Culex and Anopheles species overwinter as dormant adults. Eggs of certain species can remain dormant in moist soil or icy waters, hatching when temperatures become favorable.
How Heat Affects Mosquito Survival
High temperatures pose a significant threat to mosquito survival, leading to desiccation and metabolic stress. While mosquitoes thrive in warm conditions, typically between 25°C and 30°C, temperatures exceeding this range can become lethal. For Aedes aegypti, the thermal upper limit for females is around 40°C, and immature stages can survive short exposures up to 45°C.
However, sustained exposure above 35°C significantly reduces their fertility and survival. Adult mosquitoes often die when temperatures rise above 40°C. For example, adult Anopheles gambiae emerging at 36°C die within 24 hours. Larvae of Aedes aegypti and Aedes albopictus cannot develop at 40°C, and 43.3°C for 30 minutes can cause 100% mortality across all life stages for these species. Mosquitoes may seek shade during extreme heat to avoid direct sunlight and dehydration.
Factors Modifying Temperature Limits
The specific temperature at which mosquitoes die is not a single, fixed number, as several factors influence their tolerance. Different mosquito species possess varying physiological tolerances to temperature extremes. For example, Aedes albopictus exhibits higher cold tolerance than Aedes aegypti.
The mosquito’s life stage also plays a role, with eggs, larvae, pupae, and adults having distinct sensitivities; eggs often show greater resilience to cold than adult mosquitoes. Humidity levels are another important factor, especially concerning heat. High temperatures combined with low humidity can accelerate dehydration, making conditions more lethal. Prior environmental exposure and acclimation can also modify a mosquito’s temperature tolerance, allowing some populations to adapt to local thermal conditions.
Temperature’s Influence on Mosquito Life Stages
Temperature profoundly impacts the entire mosquito life cycle, influencing population dynamics and disease transmission. Warmer temperatures accelerate egg hatching rates, with optimal hatching for Anopheles gambiae eggs occurring between 24°C and 30°C. Larval development time is also reduced at higher temperatures; for instance, Culex pipiens development from egg to adult can take 29 days at 16°C but only 9 days at 28°C.
However, excessively high temperatures, even if not immediately lethal, can decrease adult lifespan and reduce overall survival. Beyond direct effects on the mosquito, temperature influences the extrinsic incubation period (EIP) of pathogens within the mosquito. This is the time it takes for a virus to develop inside the mosquito before it can be transmitted. For example, the EIP for dengue virus in Aedes aegypti shortens as temperature increases, meaning mosquitoes become infectious more quickly in warmer environments. Higher temperatures can similarly shorten the EIP for West Nile virus in Culex mosquitoes, increasing transmission risk.