he mosquito species Aedes scapularis was first observed in larval form in the Florida Keys 75 years ago. A new study by Lawrence Reeves, Ph.D., and colleagues has discovered that Aedes scapularis is now established on mainland Florida in Miami-Dade and Broward counties. (Photo courtesy of Lawrence Reeves, Ph.D.)

By John P. Roche, Ph.D.

Aedes scapularis is a mosquito that can spread yellow fever, Venezuelan equine encephalitis virus, and other human pathogens. It has a wide range, from Texas to parts of South America and throughout much of the Caribbean. In 1945, three specimens of larval Ae. scapularis were found in Monroe County, Florida, in the Middle Florida Keys, but Ae. scapularis has not been seen in Florida since then—until now. A new study published in November in the Journal of Medical Entomology by Lawrence Reeves, Ph.D., of the University of Florida and colleagues from UF, the Broward Mosquito Control Section, and the Miami-Dade Mosquito Control Division reports that Ae. scapularis is now established in mainland Florida in Broward and Miami-Dade counties. This has potential significance for public health in the region.

The University of Florida study used 121 mosquitoes that had been collected in traps via routine mosquito sampling by mosquito control programs in Miami-Dade and Broward counties, and during field sampling in ecological research. The mosquitoes were identified as Ae. scapularis using morphological keys. Members of a subset of sample mosquitoes were identified by a technique called DNA barcoding.

The investigators compared the cytochrome c oxidase subunit I gene among Ae. scapularis and all related mosquitoes in the U.S. that are members of what is called the Ochlerotatus Group: Ae. condolescens, Ae. infirmatus, Ae. thelcter, Ae. tortilis, and Ae. trivittatus. Genetic analysis confirmed the morphological identification, verifying that Ae. scapularis is established in Florida. It also found low genetic divergence between sequences from two other Ochlerotatus Group species: Ae. condolescens and Ae. tortilis. The investigators then followed up with agenetic analysis of another gene (the internal transcribed spacer 2 gene) of several Ochlerotatus Group mosquitoes. As before, there was low divergence between Ae. condolescens and Ae. tortilis, suggesting that individuals identified as Ae. condolescens and Ae. tortilis may be members of the same species—a result that is an intriguing byproduct of the study.

“The central finding of the manuscript,” Reeves says, “is that Aedes scapularis, a non-native mosquito and potential pathogen vector, is now established in the southern Florida Peninsula. The Florida Strait was likely a geographic barrier for the species, and now that it has crossed that barrier, Aedes scapularis could potentially spread further northward and westward to fill any contiguous areas that are environmentally suitable.”

What is the significance of this finding? One possibility is that Ae. scapularis could vector diseases to people in Florida. “Aedes scapularis in South America and elsewhere has been found to be naturally infected with a range of pathogens,” Reeves says. “It’s hard at this point to say how Aedes scapularis might become involved in the transmission of these or other pathogens in Florida, but the species is ecologically well positioned to be a vector because it feeds readily from humans: some populations are well adapted to human-dominated habitats, they feed from a broad range of hosts, and they feed readily from humans.”

A new study published in November in the Journal of Medical Entomology reports that the mosquito species Aedes scapularis—previously detected in Florida just once, in 1945—is now established in mainland Florida in Broward and Miami-Dade counties. “Of Florida’s 16 established non-native mosquitoes, 13 were first detected in the state since 1985, and 10 were first detected since 2000,” says by Lawrence Reeves, Ph.D. (Photo courtesy of Lawrence Reeves, Ph.D.)

Another significant aspect of this study is that it could provide insights into how invasive mosquito species get into Florida. This information could help identify pathways through which mosquitoes spread, providing insights that could help mosquito control agencies reduce future establishment of new invasive mosquito species.

This whole study started when Reeves collected a female Ae. scapularis in a trap in Florida City in the summer of 2020. “At that time,” Reeves says, “we didn’t have a lot to go on towards understanding how widely this mosquito was distributed, or if the species was truly established in Florida.” A subsequent collaboration with the Miami-Dade Mosquito Control Division and Broward Mosquito Control Section helped Reeves and his colleagues develop a firm picture of the species’ presence.

There are a lot of follow-up research questions Reeves and his colleagues would like to explore. They are interested in learning how far the geographic distribution of Ae. scapularis will expand in the future. “We also hope to investigate its ecology here in the state,” Reeves says, “to get an idea about its host associations within its introduced range.”

The establishment of Ae. scapularis and other invasive species is not only geographic—it is also ecological. “Of Florida’s 16 established non-native mosquitoes, 13 were first detected in the state since 1985, and 10 were first detected since 2000,” Reeves says. “To speculate: There is a possibility that recent trends in climate, trade, and/or human movement are promoting non-native mosquitoes in Florida, and that our detection of Aedes scapularis is part of that trend.”

The establishment of invasive species is partly ecological, but, with mosquitoes, the impact is epidemiological. With more mosquito species, there could be more pathogens that can be spread to humans, or the transmission dynamics of pathogens could shift for better or worse, complicating both healthcare and mosquito control. Future research on Ae. scapularis and other invasive mosquitoes holds promise to forge ways to reduce and contain the incidence of these vectors.

John P. Roche, Ph.D., is an author, biologist, and educator dedicated to making rigorous science clear and accessible. Director of Science View Productions and Adjunct Professor at the College of the Holy Cross, Dr. Roche has published over 200 articles and has written and taught extensively about science. For more information, visit https://authorjohnproche.com/.