Malaria parasites develop faster in mosquitoes at lower temperatures than previously thought, according to researchers at Penn State and the University of Exeter. The findings suggest that even slight climate warming could increase malaria risk to hundreds of thousands, if not millions, of people—including travelers—in areas that are currently too cold for malaria parasites to complete their development. The researchers used two of the most important malaria-hosting mosquito species in the world—Anopheles stephensi and Anopheles gambiae—to conduct their experiments. They maintained these malaria-infected mosquitoes in the laboratory under a variety of temperatures ranging from 16 to 20 degrees Celsius, or 60 to 68 degrees Fahrenheit. They maintained a separate control set of mosquitoes at 27 degrees Celsius, or about 80 degrees Fahrenheit, which is the temperature at which malaria transmission is typically highest. The traditional model estimates that parasites in the mosquito take 56 days to develop at temperatures just above the minimum threshold for development—a cool 18 degrees Celsius, or 64 degrees Fahrenheit. However, the current study shows that as few as 31 days are required for such development for Anopheles stephensi. The researchers also found that variation in temperature at this cooler end of the range promotes faster parasite development. Parasites developed in as few as 27 days at 18 degrees Celsius.