Temperature & Mosquitoes

All insects, including mosquitoes, are ectothermic, more commonly referred to as “cold-blooded.” Ectotherms rely on external sources of heat, so temperature plays an important role influencing developmental processes, behaviors, and even survival. In general, higher temperatures have been found to shorten development time and decrease adult size of mosquitoes. The phenomenon of having smaller body size in response to increased temperatures is common in ectotherms and tends to be the rule rather than the exception. Although increased temperatures commonly result in smaller size, more rapid growth and development leads to increased probability of survival to adulthood. In the case of nuisance mosquitoes, this may translate into more active adults and more mosquito bites, given there is sufficient precipitation to prevent drying of larval habitats. As we enter the cooler months, we can see some seasonal trends from our mosquito surveillance in Richmond County.

Figure 1

Figure 1. Numbers of mosquitoes captured and daily temperatures. The red and blue lines represent the number of mosquitoes captured in traps among two different “routes”. Each route has 7 trap sites; and trapping occurs weekly, alternating between routes. The green line and purple line represent daily maximum and minimum temperatures respectively.

Numbers of nuisance mosquitoes have remained high in some locations through September and arboviral disease (viruses transmitted by arthropods like ticks and mosquitoes) transmission is still a possibility. However, those numbers are beginning to fall due to cooler night temperatures.

Figure 2

Figure 2. Correlation between temperature and number of mosquitoes. Each point represents the number of mosquitoes captured, averaged over one month and the daily low temperature, averaged over the same month. The R2 value in the top corner shows how well the mosquito count can be predicted or explained by the minimum temperature. In this case, about 60% of the fluctuation (variance) in mosquito counts can be accounted for minimum temperatures.

Past studies have found that the seasonal emergence of host-seeking females (those seeking a blood meal) is strongly influenced by the minimum temperature, and our results are in agreement with that finding. Furthermore, one study from Italy on the Asian tiger mosquito, a major nuisance species in our area, identified a threshold for activity around 48.2°F – 55.4°F.

Figure 3

Figure 4

Figure 3. Correlation between temperature and number of mosquitoes. The graph on the top shows the relationship when temperatures are 50F or below, and the graph on the bottom shows the relationship when temperatures are above 50F. Comparison of the two graphs shows the relationship is much stronger when temperatures are lower and there is practically no relationship once temperatures exceed 50F.

A closer examination of our data shows that numbers of mosquitoes vary by one order of magnitude (difference between 10’s and 100’s) when daily low temperatures are around 50°F. These data also show that once daily low temperatures exceed 50°F, the minimum temperature has almost no effect on the number of mosquitoes. As low temperatures in your area begin to drop consistently into the low 50’s, expect a substantial decrease in the number of mosquitoes around your home.