YELLOW FEVER MOSQUITO, ASIAN TIGER MOSQUITO
UF/IFAS Photo by Jim Castner
Blood-feeding mosquitoes are a nuisance, and some Florida species are known to transmit viruses that cause diseases in people and animals, including West Nile encephalitis and dengue fever. As UF/IFAS scientists work to determine whether Zika virus could become established in Florida mosquito populations, the invasive yellow fever mosquito and Asian tiger mosquito merit special concern because they are believed to transmit Zika virus in other countries.
Estimated economic losses: a single, severe case of a mosquito-borne viral disease such as West Nile encephalitis can result in millions of dollars in medical costs.
Estimated management costs: difficult to estimate, because the yellow fever mosquito and Asian tiger mosquito are container species that lay eggs in very small bodies of water.
Florida is home to about 80 mosquito species. Of these, all but one feed on blood provided by vertebrate hosts, though many species rarely, if ever, bite people.
About 33 of the blood-feeding species are considered pests, because they are relatively common and regularly feed on human hosts. These species contribute to the state’s overall arthropod-related expenditures, because mosquito control represents a large, unavoidable expense for many local governments. The total economic impact of blood-feeding mosquitoes also includes consumer spending on repellents and other preventive measures. What’s more, 13 species of blood-feeding mosquitoes found in Florida can transmit diseases to people and animals, meaning that Florida’s overall mosquito-related economic burden includes health-care costs for people and animals suffering from mosquito-borne illnesses.
Two closely related species, the yellow fever mosquito and Asian tiger mosquito, rank among the most widespread and troublesome disease-carrying mosquitoes found in Florida. Currently, they are the subject of intense scientific interest due to their apparent role in transmitting Zika virus in the Caribbean, Central and South America, and some Pacific islands.
Common Names: Yellow fever mosquito; Asian tiger mosquito
Scientific Names: Aedes aegypti (yellow fever mosquito); Aedes albopictus (Asian tiger mosquito)
Good Bugs or Bad Bugs? Bad Bugs
What They Are: Like all blood-feeding mosquitoes, the yellow fever mosquito and Asian tiger mosquito are members of the insect order Diptera, and the family Culicidae. To be more specific, both species are members of the genus Aedes, which contains dozens and dozens of species, all of them day biting mosquitoes, though many species do not actively seek out human prey and instead prefer other hosts.
As with all blood-feeding mosquitoes, only the female yellow fever and Asian tiger mosquitoes bite people, doing so to obtain nutrients they need for egg production. Unfortunately, if a female mosquito feeds on a host that is already carrying a pathogen in its bloodstream, she may ingest the pathogen along with the host’s blood. If the mosquito’s immune system doesn’t destroy the pathogen, the pathogen may replicate and if it can escape the gut, it can potentially spread throughout her body, eventually reaching her salivary glands. If this happens, the mosquito can potentially transmit the pathogen to future hosts, because mosquitoes inject saliva into the bite wounds they make, as part of the feeding process.
Blood-feeding mosquitoes are said to be “vectors” for the pathogens they transmit, and the act of transmitting pathogens is technically called “vectoring” them. Viruses vectored from arthropods to their hosts – people and other vertebrate animals – are called arboviruses. You can learn more about the terms “vector” and “arbovirus” in this week’s Bug Word of the Day selections, on the Bug Week website, http://bugs.ufl.edu.
What They Do: The yellow fever mosquito and Asian tiger mosquito are called “container” mosquito species because females lay eggs just above the water line inside small containers that hold water. Those containers might be empty cans or bottles, tires, wheel barrows, buckets, anything that holds water. Both species are day-biting mosquitoes, although they’re most active just after sunrise and just before sunset.
Who Is Affected: Potential targets for the yellow fever mosquito and Asian tiger mosquito include virtually anyone who sets foot outdoors in Florida during pleasant weather.
Where They’re Found in Florida: Because yellow fever mosquitoes and Asian tiger mosquitoes are capable of completing the immature stages of their life cycles in very small bodies of water, they have successfully adapted to life in human-built environments. Adult females’ egg-laying efforts are aided by the presence of litter, outdoor fixtures and other potential water-holding sites that people provide. One physical characteristic affects the distribution of yellow fever and Asian tiger mosquitoes – they are not strong fliers. As adults, these two species do not disperse far from the habitats where they developed as larvae, meaning that local infestations can persist for years if not addressed properly.
How the Problem Is Currently Addressed: Experts agree that reduction of local mosquito populations is the most effective way to reduce local incidence of mosquito-borne diseases and reduce the nuisance that blood-feeding mosquitoes present.
Florida has a highly organized and well-funded mosquito-management program, which includes participation by UF/IFAS, USDA, the Florida Department of Agriculture and Consumer Services, the Florida Department of Health, 61 mosquito control programs statewide, county Extension offices and the Florida Mosquito Control Association.
For the past several decades, large-scale mosquito-control programs have focused on the species that can transmit viruses responsible for eastern equine encephalitis, St. Louis encephalitis and West Nile encephalitis. The targeted mosquito species feed at night and lay rafts of eggs on the surface of open water bodies including water accumulated in crop furrows, storm drains and flooded areas. The insecticide applications used to target these species do not address the yellow fever mosquito and Asian tiger mosquito effectively.
One standard insecticide-application route involves nighttime insecticide spraying that is meant to kill night-flying adult mosquitoes. The yellow fever mosquito and Asian tiger mosquito do not generally fly after full darkness descends, and it is not practical to conduct spraying during the day, because higher daytime temperatures cause liquid chemicals to evaporate faster, and because people are more active during the day and thus more likely to encounter the insecticide.
Another standard insecticide-application for mosquito control involves application of larvicides (insecticides that kill mosquito larvae) to swamps, ponds, lakes and other relatively large bodies of open water where mosquito larvae dwell. The yellow fever mosquito and Asian tiger mosquito do not lay eggs at such locations. Municipal programs are unable to reach or eliminate the tiny larval habitats these species prefer, so the responsibility for eliminating container-mosquito breeding habitat falls to individual home, business and property owners.
Native to Florida? Neither species is a native insect.
The yellow fever mosquito is originally from Africa and has been present in the Western Hemisphere for hundreds of years. In fact, Florida’s public mosquito-control efforts came about in response to a terrible yellow fever epidemic in Jacksonville in 1888 that killed 400 people and crippled the city’s economy. (Yellow fever is no longer a significant concern in Florida – the last reported case in North America was in 1905, and there is a vaccine available against the disease now.)
As its name implies, the Asian tiger mosquito is native to Asia, specifically the southeastern part of the continent. This species was first documented in the U.S. in Texas in 1985. One year later, it was found in Florida at a tire dump site near Jacksonville, in Duval County. Since then, the species has spread to all 67 Florida counties. The arrival of the Asian tiger mosquito has been correlated with the decline of yellow fever mosquito populations in some Florida environments. This trend has been investigated by UF/IFAS researchers, because the Asian tiger mosquito is a more efficient vector of the virus that causes Dengue hemorrhagic fever, one of the state’s more troublesome mosquito-borne viruses in recent years. However, recent research indicates that yellow fever mosquito populations are no longer in decline and are increasing in some parts of Florida.
Big Money Associates: About 20 mosquitoes from the Aedes genus are found in Florida, but besides the yellow fever mosquito and Asian tiger mosquito, only one of them is well-known. That’s the native black salt marsh mosquito, Aedes taeniorhynchus, which is found along much of the U.S. Eastern Seaboard, and is common in coastal areas throughout the Caribbean, along the Gulf and Pacific coasts of Mexico and Central American nations, and in coastal regions of several South American nations. This mosquito is not a significant disease vector, but it is an aggressive biter and is so abundant in many of Florida’s coastal communities that it’s been a high priority for government mosquito-control programs since their inception.
Interesting Fact: The Asian tiger mosquito is believed to have entered the U.S. (and many other countries) via international shipments of used automobile tires.
Estimated Economic Losses: Although there are no precise figures available that tabulate the health-care costs imposed on Floridians by container mosquitoes, a study using 1990 financial figures estimated that lifetime care for one person suffering from a severe case of eastern equine encephalitis could total $3 million, and treatment for a milder case could total $21,000 for short-term healthcare.
Thus, it seems reasonable to assume Floridians may incur hundreds, if not thousands of dollars in medical costs for any mosquito-borne illness that causes symptoms serious enough to require medical care.
The Florida Department of Health maintains records on mosquito-borne illnesses reported in the state, including the location where it’s believed the infection was acquired. Locally acquired cases are noted, as are “imported” cases, where the patient was diagnosed in Florida but is believed to have contracted the disease elsewhere. Imported cases are often more prevalent, but locally acquired cases still occur, sometimes unexpectedly or even inexplicably. For example, Florida’s last 20th-century case of Dengue fever took place in 1934, then the disease seemingly disappeared from the state for 75 years, reappearing in the Florida Keys in 2009. Dengue has had a small but notable presence in the state ever since, with a handful of locally acquired cases reported each year. This is strong evidence that Florida’s mosquito-borne virus landscape is multifaceted and difficult to predict.
Estimated Management Costs: This would be difficult to estimate accurately. Despite the fact that municipal mosquito control programs have limited success using chemical control measures against container mosquitoes, some programs include a strong outreach component that includes one-on-one contacts with residents, providing education, on-premises assistance at clients’ homes, and instruction on the use of larvicidal products suitable for use in small containers such as birdbaths. In addition, individual home and property owners devote an unknown amount of time, effort and resources to eliminating container mosquito habitat and purchasing repellents and similar products intended to reduce mosquito presence.
What UF/IFAS Is Doing About It: Since 1954, the Florida Medical Entomology Laboratory (FMEL) in Vero Beach has supported vital research on mosquitoes, notably those that have health impacts on the state, such as the yellow fever mosquito and Asian tiger mosquito. When word of the Brazilian Zika outbreak reached the mainstream news media, FMEL experts were already deep into investigations on the mosquito species that transmit Zika. Those investigations focus on topics that include ecology and invasion biology, mosquito-virus interactions, potential control strategies and new tools to detect Dengue and chikungunya viruses. This research has been funded by the National Institutes of Health and the Florida Department of Agriculture and Consumer Services.
Researchers at FMEL and USDA laboratories research issues related to mosquito-borne diseases, including mosquito ecology, the epidemiology of mosquito-borne diseases, the ability of specific mosquito populations to vector specific diseases, and genetic factors that influence the odds that a mosquito will become infected by a virus it ingests with a blood meal.
Regarding Zika virus, UF/IFAS research has spent years investigating numerous basic and applied-science issues related to the yellow fever mosquito and Asian tiger mosquito, such as their living habits as larvae and adults, adult females’ feeding habits, competition between the species, potential attractants and repellents, and similar topics. Recently, a team of UF/IFAS researchers visited Brazil to collect mosquito samples and attempt to determine whether Brazilian populations of the yellow fever mosquito and Asian tiger mosquito are commonly infected with Zika and other pathogenic viruses. The results will help scientists determine the likelihood that Florida mosquito populations could actually transmit Zika virus, an event that has not taken place, so far as scientists are aware.
What YOU Can Do About It: Every Florida resident can take action to help reduce local populations of the yellow fever mosquito and Asian tiger mosquito. Because these species tend to stay in the same area for generations, when you take action it will pay off quickly by reducing mosquito populations on your property.
UF/IFAS experts suggest that homeowners inspect their yards every week and discard or store containers that may collect rainwater outdoors so that they don’t become a place for container mosquitoes to lay eggs. For items such as bird baths, water should be treated with an appropriate larvicide or changed out weekly and the inner walls scrubbed to remove eggs. Experts also suggest wearing appropriate clothing and applying mosquito repellent before venturing outdoors.
The Bug Week Web Team has prepared a feature story with more detailed information on reducing mosquito populations on your property.
Read more about container mosquitoes in this document from the UF/IFAS EDIS online Extension library.
Read more about the yellow fever mosquito in this “Featured Creatures” document from the UF/IFAS Entomology and Nematology Department.
Read more about the Asian tiger mosquito in this “Featured Creatures” document.
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