Invasion of Mosquitoes into New Areas

Stephanie Richards, PhD, Medical Entomologist

Globalization and Spread of Mosquitoes

With many mosquito borne pathogens using human hosts as the reservoir (i.e., host capable of infecting mosquitoes), human travel is also potentially increasing the risk of pathogen spread into indigenous mosquito populations. For instance, humans are the primary reservoir host for dengue, chikungunya, and Zika viruses, mosquito borne pathogens that have received a lot of news coverage in the United States in recent years.

What are some examples of invasive mosquitoes that have affected the United States?

Aedes aegypti (the yellow fever mosquito) originated in Africa and has been in the United States since the 17th century. This is a historically forest dwelling mosquito, but human development and fragmentation of forested areas may have facilitated the adaptation of this mosquito species for living near human dwellings.

Shipping and trade activities also likely helped Ae. aegypti colonize many countries in the Tropics. A recent United States study showed that Ae. aegypti has been reported in 26 states and the District of Columbia between 1995 and 2016. Today, Ae. aegypti is considered the primary vector of dengue, chikungunya, yellow fever, and Zika viruses, due to its ability to become infected with and transmit these viruses, coupled with its human blood feeding preference.

Before 1985, when I>Ae. albopictus (Asian tiger mosquito) was first detected in Texas from a shipment of tires from Asia, none of these mosquitoes had been detected in the United States. In the United States, Ae. albopictus has been reported in 40 states and the District of Columbia. This mosquito can also serve as a vector of the same viruses transmitted by Ae. aegypti (e.g., dengue, chikungunya, yellow fever, Zika viruses) as well as other viruses such as West Nile virus. Aedes albopictus takes blood from a variety of animals, including humans.

Aedes japonicus (Asian bush mosquito) has been present in northern North America since approximately 1998 and has since spread to 31 southern and western states in the U.S. A study examining genetic diversity of Ae. japonicus in Virginia found that mosquitoes collected along an interstate corridor were related. The same study hypothesized that human travel between states may be contributing to the establishment of this species in new areas.

Aedes aegypti, Ae. albopictus, and Ae. japonicus females lay their eggs in natural and artificial containers, hence could be considered competitors for resources in these containers. However, differences in their biology and behaviors may contribute to their relative success.

For example, in temperate regions, Ae. japonicus is most abundant early in mosquito season, while Ae. albopictus becomes abundant later in the season, hence there is little overlap in competition of these two species. Aedes aegypti thrives in subtropical and tropical climates, while Ae. albopictus can thrive in subtropical, tropical, and temperate regions. Aedes albopictus may outcompete Ae. aegypti in environments with limited resources. Satyrization (competitive mating) of Ae. aegypti by Ae. albopictus, where Ae. albopictus males mate with Ae. aegypti females, essentially sterilizing Ae. aegypti females, may be a factor contributing to the rise of Ae. albopictus (and decrease of Ae. aegypti) in some areas. Although the effects of this competitive mating dissipate over time as Ae. aegypti adapts, mosquito fitness costs may reduce reproductive success of this species over time in these areas.

Recent Detection of Invasive Mosquitoes into the U.S.

In late-2016, two additional invasive mosquito species (Aedeomyia squamipennis and Culex panocossa) were found in Florida. Aedeomyia squamipennis takes blood primarily from birds, hence may play a role in maintenance of viruses such as West Nile. Culex panocossa is native to Central America, South America, and the Greater Antilles. This species may be involved in the transmission of the Everglades virus in Florida as it is a good vector of Venezuelan encephalitis virus (related to the Everglades virus) in its native range in Central America.

Since global trade and travel will continue, it is important that to support local longitudinal mosquito surveillance and control efforts to assess/manage risk, provide institutional knowledge of the occurrence and abundance of native and invasive mosquitoes, and protect public health.

It is important to note that not all mosquito species invading the U.S. will become established and spread widely. Surveillance-based targeted mosquito control as part of an integrated mosquito management program may help limit the spread of invasive species.

References

Blosser E, Burkett-Cadena N (2017) Culex (Melanoconion) panocossa from peninsular Florida, USA. Acta Tropica 167:59-63.

Egizi A, Kiser J, Abadam C, Fonseca D (2016) The hitchhiker’s guide to becoming invasive: exotic mosquitoes spread across a US state by human transport not autonomous flight. Molecular Ecology 25:3033-3047.

Hahn MB, Eisen RJ, Eisen L, Boegler KA, Moore CG, McAllister J, Savage HM, Mutebi JP (2016) Reported distribution of Aedes (Stegomyia) aegypti and Aedes (Stegomyia) albopictus in the United States, 1995-2016 (Diptera: Culicidae). Journal of Medical Entomology 53:1169-1175.

 

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