The temperature of the environment is critical to the growth of organisms that cannot generate their own heat, including insects. As a general rule, the warmer the environment, the faster an insect grows, at least in part because their metabolism increases with increased temperature. This speedy development does come with a cost: smaller size as an adult. Likewise, cooler temperatures result in larger adults. As adult size, at least for females, correlates with the number of off-spring that can be produced, it seems like it would be better to be cool than hot.
However, temperature preference studies (well, the one that exists) show mosquito larvae of Aedes aegypti prefer warmer temperatures. This may be because the long-development at cooler temperatures exposes the water-bound larvae to increased risk of a habitat drying out.
To better understand how temperature affects mosquito larvae, we conducted an experiment assessing Aedes aegypti larval foraging behavior at different temperatures and nutritive environments. We expected foraging activity would increase as temperature increased, in order to keep up with metabolic activity. We also expected larvae in low-nutrient environments to forage more actively to obtain enough nutrients to turn into a biting mosquito.
We used a traditional approach of classifying behavior and scoring individuals through video recording. This was an arduous process, and the above image gives you an idea of the kind of behaviors we had to carefully observe to score (the video image shows movement “shadows” that correspond to the line drawing from Walker and Merritt, 1991).
We found that, indeed, at low nutrients larvae foraged more actively. What was surprising was that foraging activity increased at both high and low temperatures, relative to a moderate temperature. At high temperature, the mosquito metabolism is increased, and larvae likely have to forage actively to keep up with demand. We suspect that at low temperatures, growing mosquitoes must contend with operating a big body (which is energetically costly) while trying to exit the non-permanent aquatic environment as quickly as possible. This makes them “hungry” and requires more active foraging, akin to what we see when we expose larvae to a nutrient-poor environment.
This is the first study of its kind, and you can get all the details here.
