Expansion of a Disease-Carrying Mosquito into the Rocky Mountains

Capable of spreading severe diseases, the Aedes aegypti mosquito is notorious for its affinity for human blood, making it a considerable challenge for eradication efforts.

Tim Moore, who oversees a mosquito control district in the Western Slope of Colorado, is particularly wary of this species.

Moore notes, "These mosquitoes have a strong preference for human blood meals."

Originally from tropical and subtropical regions, the Aedes aegypti is migrating due to rising global temperatures and altered precipitation, now posing a threat by transmitting viruses like Zika and dengue in areas beyond its usual habitat.

This species is now being detected in unexpected places within the Mountain West, areas previously deemed too inhospitable. Over the past ten years, various locales have reported their presence consistently.

Most recently, Grand Junction in Colorado, renowned for its challenging climate, has become yet another home for these unwelcome insects.

With around 70,000 residents, Grand Junction is Colorado’s largest city west of the Continental Divide. The mosquito was first detected there in 2019, seemingly an anomaly since the species was also identified in Moab, Utah, miles away.

Initially dismissed as a random occurrence by Moore, this perception changed when more Aedes aegypti mosquitoes were captured in subsequent years.

“Coincidence is rarely a term used in scientific inquiry,” remarks Hannah Livesay, a biologist with the Grand River Mosquito Control District.

Despite skepticism grounded in scientific literature predicting their brief tenure due to harsh winters, the mosquitoes proved resilient.

In 2024, the district reported capturing 796 adult mosquitoes and locating 446 eggs. Rather than merely surviving, the mosquitoes prospered.

Increasing Risks of Dengue Transmission

Mosquitoes are deemed incredibly hazardous due to their role in transmitting potentially deadly diseases, primarily malaria, spread by Anopheles mosquitoes.

However, researchers are increasingly concerned about dengue, a disease enabled by the expanding range of Aedes aegypti bolstered by climate change, prolonged fall seasons, and elevated altitudes.

Dengue cases, reported globally, surged between 2000 and 2024, as urban growth and international mobility facilitated the mosquito’s spread.

While the disease can often be mild, it has the potential for severe and excruciating symptoms, though outbreaks have led to thousands of deaths annually.

Although the mosquito species is present in Grand Junction, medical entomologist Chris Roundy mentions that public health officials currently consider the risk of disease transmission low.

Mosquitoes must feed on an infected individual to spread disease, a relatively uncommon scenario.

Nevertheless, vigilance remains crucial should the mosquito's presence expand geographically or the potential for disease carrying increases.

Efforts to Contain Aedes aegypti Populations

David Garrett leads the control efforts within Grand River Mosquito Control District’s Aedes aegypti initiative, operating predominantly in Orchard Mesa.

Even as operations to combat West Nile virus slow down across Colorado, Garrett’s team continues active monitoring for Aedes aegypti.

Traps positioned close to human activity serve to lure mosquitoes in, utilizing the mosquito’s preference for container habitats.

The species thrives in artificial environments and lays eggs across multiple locations, complicating eradication efforts.

Efforts to inform and involve the community have been gradual but vital for effective control, especially given the mosquito’s costly mitigation.

Moore emphasizes the need to either eradicate or limit the species to prevent significant spread.

The Need for Harsh Winters

The method of introduction remains unclear, though possibilities include transported plant containers.

Robert Hancock, a specialist in mosquito ecology, notes the mosquito’s adaptability as concerning, particularly its survival through winter seasons.

While rising temperatures contribute to more frequent occurrences, the lack of freezing temperatures in winter supports mosquito endurance.

A return to severe winters is necessary for restraining mosquito survivability and presence in Colorado.