Why Are Mosquitoes Crossing State Lines?

Written by Kelsey Renfro, Ecologist, Taxonomist, and Laboratory Manager in Colorado



Generally, in Colorado, we spend day after day digging through piles of Aedes vexans, Culex pipiens, Culex tarsalis, and several other common species. When it comes to adult mosquito surveillance, our Denver office alone sets and collects over 200 traps per week. It can get pretty exciting while sorting through a pile of mosquitoes, during your normal monotonous routine, when a specimen that doesn’t seem to belong appears under your microscope. After running the unique arthropod through a dichotomous key (an identification tool), the excitement is heightened when you realize you have found a mosquito species never previously recorded in your state! In a single season, our Denver lab identified three (3) species that lacked historical records in the state of Colorado. Needless to say, our team was intrigued by the new discoveries and took on the challenge to monitor their presence during the remainder of the season as well as throughout the next year.

The obvious question was, “Why are new species entering Colorado?” The state has seen a substantial increase in people moving in over the last decade. Could the influx of human residents be playing a role in the introduction of the 6-legged residents? Are changes by Mother Nature contributing to the mosquito species crossing state lines? Or a combination of the above?
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Mosquito of the Month: Culex erraticus

Written By Courtney Brown, Surveillance Technician

Continuing the theme of mosquitoes of diminutive stature, this month we focus on another small mosquito – the tiny and mighty Culex erraticus.

Culex_erraticus-Carpenter-and-Lacassee_1955_250.jpgIn contrast to the beautiful, benign Uranotaenia lowii of last month, Culex erraticus is dressed more plainly in rich chocolate brown from proboscis to toe with lighter tan banding on the abdomen. Their size is not to be underestimated; they come equipped with a long proboscis with the business end being swollen. Their bite is regarded as painful, with the added insult of being accompanied by a vector-borne disease at times. Even though sorting through great masses of tiny brown mosquitoes quickly becomes monotonous, these tiny mosquitoes are of great interest to mosquito management programs due to their appetite for birds, large hooved mammals, reptiles, amphibians, and humans.

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Mosquito of the Month: Uranotaenia lowii – the Pale-Footed Uranotaenia

Written By Theodore Heron, Surveillance Technician

Beauty can be found in the smallest of things. Last month we focused on the largest mosquito, or “elephant mosquito,” Toxrhynchites rutilus. However this month, we are at the opposite end of the spectrum with the smallest mosquito —Uranotaenia lowii, also known as the pale-footed Uranotaenia.

http://cdn2.hubspot.net/hubfs/581508/Uranotaenia%20lowii_University-of-Florida.jpgMuch like its overly-sized relative, the pale-footed Uranotaenia has no interest in humans. This lack of interest, combined with its small size, leaves the species often unnoticed in mosquito management and surveillance programs. While the mosquitoes ignore humans, other living creatures aren’t as fortunate. The tiny mosquitoes get their blood-meals from reptiles and amphibians—mostly frogs. Throughout the world, amphibian populations are drastically declining, and many scientists believe habitat destruction and climate change are the primary culprits. Very little is known about how mosquitoes affect non-human species. So, this is entirely speculation, but vector-borne disease may be an additional contributor to this decline. Uranotaenia lowii resides within several pockets of the Western Hemisphere, including the U.S. Gulf states from Texas to Florida, and along the Atlantic seaboard, as far north as North Carolina.

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Mosquito of the Month: Toxorhynchites rutilus – the Elephant Mosquito

Written By Michael “Doc” Weissmann, Ph.D., Chief Entomologist

“Massive” and “giant” are not terms most of our partners want to hear associated with insects, especially mosquitoes, in their community. Toxorhynchites rutilus is the largest mosquito in the USA. An adult female can have a wing span of nearly ½ inch, and if it sat on a quarter, the tips of their long legs could dangle off the edges. Yeah, I’d call that massive.

Toxorhynchites_rutilus_septentrionalis_DallasTX_JasonWilliams250.jpgBut fear not – these giant, day-flying mosquitoes do not need a blood meal to produce eggs, so they do not bite. Due to their lack of interest in taking a nibble, they are only caught in certain kinds of traps associated with mosquito surveillance, and cause little concern in the field of mosquito control. Both adult males and females feed exclusively on sugary substances – primarily flower nectar but also plant sap, honeydew, and juices from rotting fruit. They are sometimes called “elephant mosquitoes” due to their long, trunk-like proboscis that curves downward and is pointed at the tip to assist in sucking nectar from deep flowers. Since they don’t bite, they also don’t transmit any vector-borne diseases. Whew!

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Mosquito of the Month: Aedes aegypti

Aedes aegypti

Mosquito of the Month: Aedes Aegypti – The Yellow Fever Mosquito

Written By: Michael “Doc” Weissman, Ph.D, Chief Entomologist

“Celebrity status” isn’t generally something bestowed upon an insect. And yet one mosquito, Aedes aegypti, has been a part of the Zika headlines almost daily for much of the last year, garnering nearly as much attention from the press as the presidential candidates during this election year.

No other mosquito species has had such a dramatic impact on human history. Also known as the Yellow Fever Mosquito, Aedes aegypti was the first mosquito implicated as a vector of human disease. Experiments in the 1880’s by Cuban physician, Carlos Finlay, demonstrated that when one of these mosquitoes took a blood meal from a patient with Yellow Fever, it could transmit the disease to a healthy person just a couple days later during a subsequent bite. Initially, few people – including members of the scientific community – took the idea seriously, finding it hard to believe that such a small insect could kill a full grown person. It took a couple of decades and many additional experiments to finally prove Finlay’s theory.

yellow fever mosquito 2Today, many mosquito species have demonstrated the ability to be competent vectors of a variety of mosquito-borne diseases affecting not only humans but also many other animals. Aedes aegypti not only carries Yellow Fever, but is also a vector of West Nile viruschikungunyadengue, and more recently making the news as the primary vector of the Zika virus. While a vaccine exists now to protect us from Yellow Fever, vaccines for the other diseases are still under development and keeping a close eye on the Aedes aegypti species remains a top priority in many Integrated Mosquito Management (IMM) programs.

The reports in the news focus on this mosquito’s role as a disease vector, labeling it as an evil species worthy of extinction. In fact, current research is developing technologies that may allow us to eradicate this species completely in the not-too-distant future, an ethical dilemma during a time when millions of dollars are spent annually to protect other species from extinction. As an entomologist, I find it hard not to admire the adaptability of this mosquito that only a few hundred years ago existed unnoticed by most humans in the dense tropical forests of Africa. Centuries of shipping trade, especially the trans-Atlantic transport of African slaves in the early-16th through mid-19th centuries, have spread Aedes aegypti (and diseases that it carries) around the world, establishing permanent populations in warmer climates.

Asian tiger mosquito_Aedes_Albopictus-1Like the closely related Asian Tiger Mosquito (Aedes albopictus), the Yellow Fever mosquito is quite beautiful on a microscopic scale. Jet black scales adorn the body and legs, marked by bright silvery-white scales on the sides of their thorax and abdomen, and ringed with white bands on each leg segment. A distinctive pattern of white scales form a “lyre-shaped” pattern on the top of the thorax. [What is a “lyre” you ask? It is that miniature harp-like string instrument that was a favorite of ancient Greek musicians.]. This is a stunning beauty as mosquitoes go.

Several features of this mosquito’s natural history have allowed it to adapt to life around humans successfully. In their native African forests, rain-filed containers, especially those found in tree-hollows, served as home to the larval stage of the mosquito. Females lay eggs just above the water surface, such that when the container fills, the eggs are flooded and hatch. The eggs can remain dry for years without hatching, waiting for rain water to flood them. Human habitations are surrounded by similar small watery containers, including rain gutters, flower pots, bird baths, and even children’s toys that could serve as larval habitats for the Yellow Fever mosquito. 

Ironically, many cemeteries where victims of Yellow Fever are buried have flower vases attached to the tomb stones, holding enough water to serve as larval habitat for more Yellow Fever mosquitoes. One of the most effective ways to control this species is to simply eliminate water containers around the home where the larvae could live. These mosquitoes are also daytime fliers, a challenge for control programs that only target the adults since daytime pesticide fogging can increase the likelihood of negative impacts on non-target insects.


Will the Yellow Fever Mosquito be allowed to continue impacting human history through the spread of disease? We have the capability to reduce their populations and thereby reduce the incidence of diseases that they vector. Perhaps we are within our right to eradicate it from most of the planet, especially since humans are responsible for expanding this mosquito’s range around the world. However, perhaps extinction is more than it deserves, and relict populations of this beautiful insect can be allowed to persist in the dense uninhabited forests of its native Africa.

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VDCI_Logo_squareSince 1992, Vector Disease Control International (VDCI) has taken pride in providing municipalities, mosquito abatement districts, military bases, industrial sites, planned communities, homeowners associations, and golf courses with the tools they need to run effective integrated tick and mosquito management. We are determined to protect the public health of the communities in which we operate. Our tick and mosquito management professionals have over 100 years of combined experience in the field of public health, specifically vector disease control. 

Michael_Doc_WeissmanPhD.jpgMichael “Doc” Weissmann is the Chief Entomologist at Colorado Mosquito Control, a VDCI company. He has been identifying mosquitoes since the mid-1980s, and has been in charge of the Surveillance Laboratory at CMC since 2003. Doc received his B.A. and M.A. in Biology from the University of Colorado, and his Ph.D. in Entomology from Colorado State University. He can be reached through the VDCI website or by calling 800.413.4445.

Mosquito of the Month: Anopheles quadrimaculatus – Common Malaria Mosquito

Written By Michael “Doc” Weissmann, Ph.D., Chief Entomologist

Malaria was eliminated from the United States by 1951. Elimination means it is gone, right? Forever? Well, not exactly.

http://cdn2.hubspot.net/hubfs/581508/Anopheles_quadrimaculatus_p_web.jpgAccording to the Centers for Disease Control and Prevention (CDC), about 1,500 cases of malaria are diagnosed each year in the U.S., predominantly in travelers or immigrants coming from countries where malaria transmission is common, primarily from sub-Saharan Africa and South Asia. Could malaria make a come-back in this country? It is not out of the realm of possibility. The malaria parasite (Plasmodium) that causes the disease symptoms in humans was almost eliminated in North America through targeted mosquito control efforts in the early 1900s that included large-scale mosquito spraying (including the use of DDT), and swamp drainage. However, Anopheles quadrimaculatus – one of the primary carriers of the disease parasite in pre-1950s U.S. – is far from eradicated.

Also known as the Common Malaria Mosquito, Anopheles quadrimaculatus is distributed throughout the eastern United States, often occurring in huge numbers in the southeastern states, especially along the Gulf of Mexico. This fact reinforces the importance of strong surveillance and disease testing programs in areas where the species inhabits. It is not unusual for VDCI’s surveillance traps set in the Mississippi Delta region to collect over 7,000 mosquitoes in one night, of which 99% are likely to be this species.

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Mosquito of the Month: Culex tarsalis – the Western Encephalitis Mosquito

Written By Michael “Doc” Weissmann, Ph.D., Chief Entomologist

Culex_tarsalis_p_2Western_Encephalitis_Mosquito_250.jpgCulex tarsalis is one of “…a number of species of which little is known and which are not, as a rule, common or troublesome….” This is how Evelyn Groesbeeck Mitchell described this species in her 1907 book, Mosquito Life. By this time, it was already established that malaria was transmitted by Anopheles mosquito species, and that Aedes aegypti was the vector of Yellow Fever. The link between mosquitoes and some forms of encephalitis was not yet known.

Today, Culex tarsalis is also known as the Western Encephalitis Mosquito. It is a species of concern throughout much of the United States, especially west of the Mississippi River, for its competency when it comes to vectoring several forms of encephalitis. In many areas, this species is the primary vector of Western Equine encephalitis, St. Louis encephalitis, and more recently, West Nile virus. Although usually preferring to seek birds as a blood meal source, they also readily bite other animals, transferring these diseases from the bird reservoir to some mammals, including humans.

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Mosquito of the Month: Aedes vexans – the Inland Floodwater Mosquito

Mosquito Of The Month: Aedes vexans – The Inland Floodwater Mosquito

Cosmopolitan – a species of the world, present in many countries and absent in only a few. No mosquito fits this description better than the Inland Floodwater Mosquito, Aedes vexans. They have been collected on every continent except Antarctica and South America. In most of North America this is the dominant mosquito species, becoming less abundant at higher elevations in the Rocky Mountains and at higher latitudes in Canada, and often outnumbered along the Atlantic coast by the Eastern Saltmarsh MosquitoAedes sollicitans.

Aedes_vexans_inland_floodwater_Mosquito_250The name “vexans” is from the Latin word “vexāre” meaning to annoy, torment, or harass. In many parts of the world, this species is a major nuisance, the females biting in the evening, peaking in activity an hour or so after sunset. They are opportunistic feeders, taking blood meals from a variety of animals as available, but apparently preferring larger mammals, including cattle, horses, deer, and humans when present.

Aedes vexans is often one of the first mosquito species that new surveillance technicians learn to identify – abundant in the trap samples early in the season, very distinctly marked, and easy to recognize. Against a background of black scales, this mosquito has narrow white bands on the base of each leg segment, and the base of most abdominal segments is adorned with white-scaled bands, indented in the middle so that they look like the letter “B” when viewed sideways.

Floodwater Mosquito Eggs

mosquito larvae mosquito eggs mosquito habitats mosquito control mosquito preventionThis is the classic “floodwater” mosquito species. By floodwater, it means that they lay their eggs individually on moist soil above the waterline at a wide variety of aquatic habitats, including temporary pools such as detention ponds or irrigated fields, but also permanent water bodies where the water level fluctuates. They especially prefer to lay eggs where there is a lot of leaf and twig cover, helping to keep the soil moist. After a short period of drying, the eggs must subsequently be flooded with water to hatch. During periods of drought, eggs can remain dormant but viable for many years, waiting for the water to rise. Extreme flooding, like the recent natural disaster in West Virginia, may wash away dormant eggs or provide water levels that welcome several new generations of Aedes vexans – only time will tell.

If the water is too cold or clear, they will not hatch. Studies have shown that a reduction in dissolved oxygen in the water stimulates hatching, such as occurs in warmer water and when the water is full of organic material like bacteria or algae. This organic matter will be food for the developing mosquito larvae. Depending on the water temperature, it takes the larva about a week after hatching to fully grow, and then it pupates and emerges as an adult a couple days later.

As mosquitoes go, these are strong fliers, being found as far as 15 miles away from their larval birthplace. How far do they usually travel? As far as necessary to obtain the four items mosquitoes need for survival:

1) nectar – the main food source for both males and females

2) harborage – shade to escape the deadly heat of the midday sun

3) blood – only needed by females as a source of protein for egg production

4) water – a place to lay the eggs for the next generation.

All of these items can be found in any urban or suburban neighborhood, attracting these floodwater mosquitoes into close proximity with our veins.

This mosquito is multivoltine – able to produce several generations each season. Adults live on average three to six weeks, but sometimes as long as three months, giving them plenty of time to lay several broods of eggs, each requiring a blood meal to obtain the necessary proteins. Although considered to be primarily a biting nuisance species in most areas, Aedes vexans has also been demonstrated to be a competent vector of several diseases, including West Nile virus and dog heartworm. Rift Valley fever is also vectored by this mosquito. Although this disease is currently restricted to Africa, the widespread distribution of Aedes vexans creates a potential for Rift Valley fever to become a disease of concern globally should it spread beyond that continent.

Larval_Habitat_inspection_with_CDC_USVI_StCroix_250Depending on the year, Aedes vexans mosquitoes constitute 40 – 50% of the tens of thousands of specimens that I examine under my microscope each summer in my role as a mosquito surveillance entomologist in Colorado. A familiar foe, it has demonstrated an ability to adapt to a wide variety of habitats, natural and human-made. While our mosquito control efforts can reduce their larval habitats as well as their adult populations to tolerable levels, I suspect that long after humans disappear from the earth, these cosmopolitan mosquitoes will continue to thrive. 

An important component of any successful Integrated Mosquito Management (IMM) program is mosquito identification. Should you have any questions regarding mosquito identification, Vector Disease Control International (VDCI) is always available at whatever level of assistance you desire.

Michael_Doc_WeissmanPhD.jpgMichael “Doc” Weissmann is the Chief Entomologist at Colorado Mosquito Control, a VDCI company. He has been identifying mosquitoes since the mid-1980s, and has been in charge of the Surveillance Laboratory at CMC since 2003. Doc received his B.A. and M.A. in Biology from the University of Colorado, and his Ph.D. in Entomology from Colorado State University. He can be reached through the VDCI website or by calling 866.497.7167.

Mosquito of the Month: The North American Rock Pool Mosquitoes

Written By Michael “Doc” Weissmann, Ph.D., Chief Entomologist
April showers bring…mosquitoes?
rock_pool_photo_Castle_Rock_CO.jpgYes, all that spring rain that makes our gardens bloom with May flowers also supplies the water necessary to hatch the first round of this season’s mosquito eggs that have been dormant over the winter. While we tend to think of mosquito larvae as swamp insects, some occur in much smaller pools, created by springtime rains and stream overflows on rocky surfaces.

Mosquito of the Month: Aedes sollicitans – the Eastern Saltmarsh Mosquito

Written By Michael “Doc” Weissmann, Ph.D., Chief Entomologist
Mosquitoes carry diseases that can kill people. We know that now. We didn’t always.

Aedes_sollicitans_Eastern_Saltmarsh_Mosquito.jpgToday, many mosquito control programs focus on reducing mosquito abundance because some species can vector life-threatening diseases. However, before making the connection between mosquitoes and disease, it was the nuisance biting that caught everyone’s attention. The Eastern Saltmarsh Mosquito, Aedes sollicitans, was one of the first mosquitoes implicated in creating unbearable living conditions due to their nuisance biting, and one of the first species targeted in large-scale mosquito management programs.