Climate Spotlight: Why do we have more mosquitoes in Flagstaff? | Columnists



When you hear the high-pitched buzz of a mosquito, do you run inside? Twenty years ago, we could sit outside on a summer evening in Flagstaff and not worry about pesky mosquitoes. What changed?

Well, for one, Flagstaff has grown. Growth means no more wading pools, empty flower pots, clogged gutters, discarded tires and other places for mosquito larvae to grow. But that’s not all: Flagstaff’s climate has also changed, in ways that make life easier for mosquitoes.

Mosquito life cycles are affected by their environment: especially temperature, rainfall and humidity. Warmer temperatures can speed up the life cycle of mosquitoes, like our floodwater species, Ochlerotatus trivittatus, allowing faster growth and more generations per year. With climate change, spring is coming earlier and winters are now shorter and milder. Hard frosts that kill mosquitoes and their eggs have become less frequent, allowing more mosquitoes to survive. O. trivittatus lays its eggs in moist soil and those eggs are more likely to survive now as Flagstaff’s winter temperatures have warmed.

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Although the average annual rainfall in Flagstaff has not changed much, we can all attest to the fact that we have received less snowfall and more intense downpours during the monsoon season. These downpours provide larger, longer-lasting pools of standing water where mosquito larvae can thrive. Between the showers, we experienced periods of more intense drought, which can reduce small creeks to isolated puddles. Mosquitoes do not lay eggs in running water, but pools of standing water are the main breeding ground.

So we have more mosquitoes, what to worry about? Well, the highest number of O. trivittatus is already disturbing our peace. More importantly, this species of mosquito can also carry West Nile virus and Western equine encephalitis, both of which affect humans, as well as heartworm, which affects our canine friends.

Will it get worse as temperatures continue to rise? It’s hard to say exactly how O. trivittatus will grow in the future, but many other mosquito species have moved north year after year. Some of them are tropical species that carry particularly unpleasant diseases. The yellow fever mosquito, Aedes aegypti, has already established itself well in Maricopa County and has now reached Yavapai County just south of us. In addition to yellow fever, this species can carry the Zika, Dengue and Chikungunya viruses. Zika is a particularly horrific disease that causes brain defects in young children.

Our state and county health departments routinely sample mosquito populations. From April to July 2021, Arizona counties installed a total of 12,548 mosquito traps. Annual sampling results indicate that Aedes aegypti migrated north into our state. Dr Kathleen Walker, an entomologist at the University of Arizona, says: “Over the past 7 years there has been a marked northward expansion of the ankle-biting mosquito Aedes aegypti. which may be due to milder winters. He is a very aggressive biter who prefers humans to other animals, so you really notice that!”

Two species of Culex mosquitoes also occur in Arizona and have the potential to spread with climate change. Both C. quinquefasciatus and C. tarsalis can carry West Nile virus, St. Louis encephalitis, and western equine encephalitis.

Anopheles hermsi is an Arizona mosquito capable of transmitting malaria, a disease that kills an estimated half a million people each year worldwide. Malaria was brought to the United States by slave traders. Abraham Lincoln suffered from the disease. In the 1930s the federal government set up huge public works projects to clean up mosquito habitat (standing water) in the southern states and in 1946 the CDC was created to prevent the spread of malaria Across the country. Climate change could undo this success.

In order to slow climate change and mosquito migration, we need to reduce our carbon footprint in every way possible. We can leave the car at home 2 days a week by carpooling or taking the bus to work. We can plan ahead to combine runs so we don’t have to leave the aisle multiple times. One day a week, instead of driving somewhere to exercise, we can walk or run around our neighborhoods. And we need to let our elected officials know that we want them to take climate change mitigation seriously.

Patricia Ellsworth, Ph.D., Retired, American Indian Air Quality Training Program, Institute for Tribal Environmental Professionals, NAU and Northern Arizona Climate Change Alliance,

Spotlight on Climate is sponsored by the Northern Arizona Climate Change Alliance,


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