Why Are Mosquitoes Crossing State Lines?

Discover the Changes In Mosquito Behaviors

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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Whether the species was a single specimen, only visiting for the season, or have established a new presence within the state – our team of mosquito detectives enjoyed monitoring the unique finds over the last two seasons. We hope you learn something new about each species as well as appreciate our team’s perspective on the potential reasons for each species to explore a new region of the country.


Species: Orthopodomyia signifera

Primary Territory: Eastern and Southern United States
2017 Colorado Location: South-Central Colorado

orthopodomyia_signifera_mosquito_microscope-300x200_denver-CO-kelseyrOr. signifera is a tree-hole species. The species prefers to utilize nature-made containers as their larval habitats – primarily tree holes. The discovery of the species (a single specimen) in the Colorado town of Pueblo was a surprise. The region is a desert environment that has historically lacked trees, except along the streams. These riparian areas (locations adjacent to rivers or streams) were either flooded away after the spring snowmelt, cut to be burned for fuel, or used as building materials, such that the trees never grew large enough to have hollows that could hold water.

During the 2017 season, we found the Or. signifera specimen along the Arkansas River where trees now grow. The river’s water levels are now controlled by upstream dams and diversion, therefore rarely flooding even during the spring snowmelt runoff, and they are no longer harvested for building materials or fuel. Today, trees in this area are encouraged to grow to maturity due to the changes humans have made to the environment. Therefore they provide the cracks and hollows Orthopodomyia require to reproduce. The 2017 discovery was a single record.

2018 Colorado Update: Unfortunately, we did not find any more specimens of this species during the 2018 season – which limits our ability to understand how or why the first specimen was located in the region. It could represent an accidental introduction of a stowaway mosquito, brought to the state by a human driving a car or truck from a more suitable southern location; however, this does not necessarily mean Or. signifera aren’t established here. Tree hole species are not usually collected in traps in high numbers. This could have been an isolated incident, but only time will tell.


Species: Culiseta minnesotae

Primary Territory: The northern United States, especially in the colder regions of the Midwest, and into the Canadian prairie.
2017 Colorado Location: North-Central Colorado

culiseta_minnesotae_mosquito_microscope-300x200_denver-CO-kelseyrWhile Colorado has suitable habitat for Culiseta minnesotae, the species has never been recorded in the state and is suspected to be adapted to a colder climate. Our team collected Cs. minnesotae in the City of Boulder within an open space that previously was a ranch. Colorado is way out of range for this species; in fact, this is the most southern location it has been recorded. This species is quite large and adapted for taking blood meals from larger mammals such as ungulates (which include deer as well as cattle and other livestock), so it makes sense to find it where horses used to reside. We’ve only collected it at one particular trap site. However, it was collected at this site multiple times during the 2017 season.

2018 Colorado Update: Our team did not find any Cs. minnesotae during the 2018 season. The 2017 population may have been an isolated introduction, perhaps brought to the former ranch location by a horse trailer from the north. However, collecting Cs. minnesotae for multiple consecutive weeks in 2017 does tell us this species can survive here, although it probably has not established a permanent population.


Species: Aedes sollicitans (Salt Marsh Mosquito)

Primary Territory: Along the Atlantic coast from northeastern Canada, south to Florida, and along the Gulf of Mexico to Texas.
2017 Colorado Location: Eastern Colorado

aedes_sollicitans _mosquito_microscope-300x200_denver-CO-kelseyrCoastal locations are common for Aedes sollicitans as the larvae live in brackish water. They can occur inland in isolated populations from somewhat saline waters created by other non-marine sources such as runoff from over-fertilization, roadside ditches where salt is used to melt ice, and wastewater from oil and gas wells.

Our team found Ae. sollicitans in half a dozen different traps from different parts of the eastern portion of the state in 2017. It looks like a more common species that live as larvae in flooded pastures, so a couple of things could be happening here. Perhaps it has always been here, and we have been misidentifying it as Aedes nigromaculis, a species that looks very similar to the untrained eye. However, being so far from the coast, that doesn’t explain where the larvae are living. For that, we look at the expansion of irrigated agriculture, roadside ditches, and oil and gas exploration. All of the traps that collected Ae. sollicitans are in close proximity to one or more of these kinds of human-altered habitats.

2018 Colorado Update:
Since the first Ae. sollicitans record was found in Colorado, we have collected many specimens for two consecutive seasons. It is likely established here, which is not surprising as this species is known to be moving inland for quite some time now. As our Chief Entomologist, Doc Weissmann mentions, in his Mosquito of the Month blog seriesAe. sollicitans in other parts of the country have been identified 30 to as far as 100 miles from their likely breeding habitats. This species is opportunistic. If the proper habitat and niche are provided in a new area – it will thrive. While we haven’t detected a disease threat in the samples collected in Colorado, this aggressive biting species has been identified in other areas of the country as a competent vector of Eastern Equine Encephalitis (EEE) and dog heartworm.

photocollage_2019141231142The three (3) species discovered by the Denver lab made for an interesting 2017 season and kept our team intrigued throughout the 2018 season. As humans continue to alter habitat and make changes to the environment, we can expect to see more species establish in areas out of their known range, or at least make a brief appearance in the future. People will also continue to transport species from place to place. Transportation can occur with stowaways in a vehicle or hidden within products used for many trades. Some species have been known to lay their eggs on sod. The landscaping material gets wrapped up and shipped out to multiple states and simultaneously moves that species to a new area. Used tires have allowed the notorious Aedes albopictus (Asian Tiger mosquito) and Aedes aegypti (Yellow Fever mosquito) to increase their range as tires are transported to recycling facilities across the country.

These are just a couple of examples of how our impact as humans expands the geographic range of mosquitoes. As mentioned with the Orthopodomyia signifera discovery – we may have isolated incidents, but only time will tell how much of an impact that humans, as well as naturally occurring environmental changes, will have on the creation of new mosquito habitats and territories.

Contact Us to Learn More About Effective Mosquito Management Strategies:

VDCI_Logo_squareSince 1992, Vector Disease Control International (VDCI) has taken pride in providing municipalities, mosquito abatement districts, industrial sites, planned communities, homeowners associations, and golf courses with the tools they need to run effective mosquito control programs. We are determined to protect the public health of the communities in which we operate. Our mosquito control professionals have over 100 years of combined experience in the field of public health, specifically vector disease control. We strive to provide the most effective and scientifically sound mosquito surveillance and control programs possible based on an Integrated Mosquito Management approach recommended by the American Mosquito Control Association (AMCA) and Centers for Disease Control and Prevention (CDC). VDCI is the only company in the country that can manage all aspects of an integrated mosquito management program, from surveillance to disease testing to aerial application in emergency situations.

Mosquito of the Month: Culex erraticus

Exploring Mosquito Species

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

In 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.

Unlike the last few stars of the Mosquito of the Month blog, Culex erraticus behaves a little more predictably to the benefit of mosquito control programs. Gravid females (mosquitoes preparing to lay eggs) fly in search of a blood meal at dusk and dawn, often in great numbers, and respond well to the carbon dioxide baited light traps utilized by surveillance programs. Due to their fairly indiscriminate feeding habits, they have tested positively for eastern equine encephalitis (EEE) virus, St. Louis encephalitis (SLE) virus and West Nile virus (WNV), as reported by the CDC. Luckily (if you can count the exception as lucky), these mosquitoes have only been found to be competent vectors of eastern equine encephalitis virus, and don’t seem to effectively spread the other viruses they have been infected with.

person-hanging-trap-mosquito

Perhaps to make up for what small space they occupy individually, their range covers a huge swath of land. In the United States, they have been found in mosquito control traps as far north as New Jersey and as far east as Texas, and in every country between our southern border and Peru, with several vacationing on Caribbean islands. Their range focuses around the swampy areas used as their larval habitat. Adult females, after having a blood meal, lay translucent eggs clustered together tightly in a structure called an egg raft that floats atop the water until the eventual emergence of larvae. Culex erraticus larvae bear something of a resemblance to their adult form as far as their coloration goes – they’re chiefly brown with a noteworthy light brown base to their antennae. Once having emerged as adults, they do not stray very far from their swamp, to the benefit of mosquito control.

Though they do not provide the most exciting find in the surveillance lab, these tiny chocolate mosquitoes are a wealth of information to any surveillance program.

Contact Us to Learn More About Effective Mosquito Management Strategies:

VDCI_Logo_squareSince 1992, Vector Disease Control International (VDCI) has taken pride in providing municipalities, mosquito abatement districts, industrial sites, planned communities, homeowners associations, and golf courses with the tools they need to run effective mosquito control programs. We are determined to protect the public health of the communities in which we operate. Our mosquito control professionals have over 100 years of combined experience in the field of public health, specifically vector disease control. We strive to provide the most effective and scientifically sound mosquito surveillance and control programs possible based on an Integrated Mosquito Management approach recommended by the American Mosquito Control Association (AMCA) and Centers for Disease Control and Prevention (CDC). VDCI is the only company in the country that can manage all aspects of an integrated mosquito management program, from surveillance to disease testing to aerial application in emergency situations.

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.

Much 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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Toxorhynchites rutilus – the Elephant Mosquito

Mosquito_lab

Exploring Mosquito Species: The Elephant Mosquito

“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

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

“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, industrial sites, planned communities, homeowners associations, and golf courses with the tools they need to run effective mosquito control programs. We are determined to protect the public health of the communities in which we operate. Our mosquito control professionals have over 100 years of combined experience in the field of public health, specifically vector disease control. We strive to provide the most effective and scientifically sound mosquito surveillance and control programs possible based on an Integrated Mosquito Management approach recommended by the American Mosquito Control Association (AMCA) and Centers for Disease Control and Prevention (CDC). VDCI is the only company in the country that can manage all aspects of an integrated mosquito management program, from surveillance to disease testing to aerial application in emergency situations.

Mosquito of the Month: Anopheles quadrimaculatus – Common Malaria Mosquito

Exploring Malaria-Carrying Mosquitoes

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

According 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.

Female Anopheles mosquitoes lay their eggs individually on the surface of freshwater pools, preferring ponds and lakes with large amounts of vegetation, including rice fields. The eggs have floats on each side, keeping them on the water’s surface. Larvae hatch out usually within two or three days. Unlike the mosquito species previously featured in this series, Anopheles larvae lack a breathing siphon at the end of their abdomen. They rest parallel to the water’s surface and take in oxygen through palmate hairs along the abdomen. Like other mosquitoes, the pupae are active but do not feed. The entire life cycle – from egg to larva to pupa to adult – can take as little as five days when temperatures are warm mid-season, but usually requires one to two weeks for development. Adults usually live for a couple of weeks.

For a mosquito with such a deadly history for humans in North America, it is a rather frail species, with long spindly legs and a thin body. The species name, quadrimaculatus, means “four-spotted” in Latin, referring to the pattern of scales on their wings that cluster into four distinct patches, easily visible without magnification. Genetic studies have determined that this is actually a species complex – a group of at least five species that are genetically distinct, but similar enough in appearance that we cannot tell them apart morphologically with a standard dissecting microscope. Apparently, they can tell each other apart, but we do not know exactly how.

So, with such high numbers of Common Malaria Mosquitoes in some parts of the U.S., why isn’t malaria a more common vector-borne disease here? There are probably many reasons. First, a person with the Plasmodium parasite must be bitten by an Anopheles mosquito. Then, the mosquito needs to live long enough for the parasite to develop into an infective stage. Finally, the mosquito needs to bite another human to pass the parasite along. In many parts of the country where these mosquitoes are common, most houses have screened windows and many are air-conditioned. Many communities also have large-scale mosquito surveillance and control programs in place to reduce the populations to levels where disease transmission is less likely. Small localized transmission could occur, but large-scale epidemics are much less likely today.

Contact Us to Learn More About Effective Mosquito Management Strategies:

VDCI_Logo_squareSince 1992, Vector Disease Control International (VDCI) has taken pride in providing municipalities, mosquito abatement districts, industrial sites, planned communities, homeowners associations, and golf courses with the tools they need to run effective mosquito control programs. We are determined to protect the public health of the communities in which we operate. Our mosquito control professionals have over 100 years of combined experience in the field of public health, specifically vector disease control. We strive to provide the most effective and scientifically sound mosquito surveillance and control programs possible based on an Integrated Mosquito Management approach recommended by the American Mosquito Control Association (AMCA) and Centers for Disease Control and Prevention (CDC). VDCI is the only company in the country that can manage all aspects of an integrated mosquito management program, from surveillance to disease testing to aerial application in emergency situations.

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

Community-Flooding

Exploring Mosquito Species: Aedes Vexans

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.

Contact Us to Learn More About Effective Mosquito Management Strategies:

VDCI_Logo_squareSince 1992, Vector Disease Control International (VDCI) has taken pride in providing municipalities, mosquito abatement districts, industrial sites, planned communities, homeowners associations, and golf courses with the tools they need to run effective mosquito control programs. We are determined to protect the public health of the communities in which we operate. Our mosquito control professionals have over 100 years of combined experience in the field of public health, specifically vector disease control. We strive to provide the most effective and scientifically sound mosquito surveillance and control programs possible based on an Integrated Mosquito Management approach recommended by the American Mosquito Control Association (AMCA) and Centers for Disease Control and Prevention (CDC). VDCI is the only company in the country that can manage all aspects of an integrated mosquito management program, from surveillance to disease testing to aerial application in emergency situations.

The North American Rock Pool Mosquitoes

Exploring Aedes epactius and Aedes atropalpus

April showers bring…mosquitoes?

Yes, 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.

Two species of North American mosquitoes, Aedes atropalpus and Aedes epactius, are adapted to survive in rock pools – small depressions formed in stone that can hold water long enough for these insects to develop from egg to adult. Once considered to be just variations of the same species, taxonomists (scientists that deal with classification and naming of species) have found enough differences between them to justify the separation into two species. There is even some genetic evidence suggesting that there may be four distinct forms rather than two – the study of taxonomy is ever-changing as new revolutionary technologies, such as genetic analysis, are introduced. Such “revolutionary change” in science is not a new phenomenon – the introduction of relatively lower cost and more powerful microscopes in the 19th century created a similar revolution in the taxonomic study of insects, giving researchers the ability to see characters that were once considered too small to accurately distinguish. But I digress…

Adults of both rock pool mosquito species have primarily black-scaled bodies with distinct white bands on the base of each abdominal segment, and white banding on either side of the leg joints. The two species differ only subtly in details that only a nerdy entomologist would notice while looking at them under a microscope – the distance between their eyes, the relative proportion of black to white scales on the femur of the hind legs, and the presence or absence of bristly hairs on the back of the thorax. Differences between the larvae are even more difficult to distinguish, including the number of spines, known as comb scales, which adorn the end of the abdomen.

Both species are adapted to life in an uncommon and challenging habitat – rock pools. These small water bodies can dry up quickly, requiring a short larval development in order to become adults before their watery home is gone. These pools also undergo huge temperature fluctuations especially in pools that are openly exposed to midday sunshine. As they dry up, the salts and minerals in the pool concentrate, creating a situation that is toxic to most other small animals, limiting the competition these mosquitoes may face for the limited resources of a rock pool habitat. Mid-season, they may lay their eggs directly on the water’s surface, whereas in late season they attach them firmly to the rock surface for overwintering. The eggs are resistant to desiccation and freezing, waiting to hatch until the pools are filled by the first warm water of spring rains or from stream overflow.

The Western rock pool mosquito, Aedes epactius, is found in the southwestern USA from Utah, Colorado, Kansas, and Missouri, south into Central America. Aedes atropalpus, the Eastern rock pool mosquito, occurs historically along the east coast of North America from northeastern Canada, south to Georgia and Alabama, and westward to the Mississippi River. I say “historically” because their range is apparently expanding.

Some rock pool mosquitoes have found man-made containers, especially water-filled used tires, to be an adequate substitute for a rock pool. This adaptation to life in tires has allowed them to spread outside of their normal rocky range, including being found as far away as Europe! Yes, invasions are not just one-way into the USA, as some of our species also find their way into other countries. Aedes atropalpus was found in Italy in 1990, suspected to have entered the country in tires imported from North America, and has since been found in France and the Netherlands as well.

Aedes epactius has been described as an avid blood feeder, while Aedes atropalpus is sometimes autogenous – able to produce its first batch of eggs without requiring a blood meal as long as they were able to obtain sufficient nutrition during their larval development. After the first eggs, they need to obtain blood for future batches, but rarely travel far from the rock pools where they were born, hence being a biting nuisance only to humans that venture near those places.

Last October was unusually warm with occasional showers in my neighborhood, and we encountered some rock pool mosquito larvae along a nearby rocky stream, long after most mosquitoes had disappeared for the winter. I do not know if they had enough time to pupate, emerge as adults, mate, and successfully squeeze out one more generation of eggs before the snow came, but it was yet another example of how well adapted these mosquitoes are to life under conditions that are quite extreme, even by mosquito standards.

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.

Contact Us to Learn More About Effective Mosquito Management Strategies:

VDCI_Logo_squareSince 1992, Vector Disease Control International (VDCI) has taken pride in providing municipalities, mosquito abatement districts, industrial sites, planned communities, homeowners associations, and golf courses with the tools they need to run effective mosquito control programs. We are determined to protect the public health of the communities in which we operate. Our mosquito control professionals have over 100 years of combined experience in the field of public health, specifically vector disease control. We strive to provide the most effective and scientifically sound mosquito surveillance and control programs possible based on an Integrated Mosquito Management approach recommended by the American Mosquito Control Association (AMCA) and Centers for Disease Control and Prevention (CDC). VDCI is the only company in the country that can manage all aspects of an integrated mosquito management program, from surveillance to disease testing to aerial application in emergency situations.

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

Exploring the Aedes sollicitans Mosquito

Mosquitoes carry diseases that can kill people. We know that now. We didn’t always.

Today, 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.

As its name implies, the Eastern Saltmarsh Mosquito is found primarily along the Atlantic coast from northeastern Canada, south to Florida, and along the Gulf of Mexico to Texas. The larvae tolerate living in the saline wetlands that line the coastal shores, from dense marshes covering many square miles, to shallow pools fed by rainwater and high tides, and they can also be found inland in isolated brackish waters.

As mosquitoes go, Aedes sollicitans is easily recognizable even to the beginning laboratory surveillance technician. The abdomen is dark-scaled with pale bands on the base of each segment and a pale “racing stripe” of scales down the center. The legs are also dark, marked with broad white bands at the base of each segment and an additional pale band ringing the middle of the first tarsal segment. The primarily black proboscis is also marked by a distinct band of white scales ringing the middle. These contrasting patterns of dark and pale scales give the species a distinct appearance – quite handsome.

Females of this species are aggressive biters, taking blood-meals from many kinds of animals including birds, reptiles, and mammals – especially humans. The species name sollicitans is Latin, meaning “vexing” or “disturbing.” They bite aggressively day or night, and even mosquitoes that are resting in the tall grasses by day will quickly take flight once disturbed and attack anyone walking thru the area. However, the feature that makes this species especially challenging is their extremely long flight distances. From April through October (and often year-round in the southern regions), large, fierce populations of saltmarsh mosquitoes can be found more than 30 miles inland from the nearest coastal swamp, with reports of individuals as far as 100 miles from their likely larval habitats.

john bernhardt smithLet’s turn back the clock for a moment to the late 1800’s, when science was only beginning to discover that some mosquitoes vector diseases and their nuisance biting was the main concern. It was also widely believed that mosquito adults never traveled far from the water where they lived as larvae. John B. Smith, former assistant entomologist at the Smithsonian in Washington DC, was hired by Rutgers University to serve as an entomologist at the New Jersey Agricultural Experiment Station in New Brunswick. A young man in his early thirties, Dr. Smith was soon faced with an annual summer infestation of saltmarsh mosquitoes that chased tourists and potential homeowners away from growing coastal resorts. He determined that the adult female mosquitoes biting him at his home likely flew there from as far as 40 miles away. It was immediately clear that any successful control measures would need to be coordinated regionally, focusing on the distant coastal marshes that served as the source of infestations experienced further inland. The early 1900s saw extensive draining of coastal marshlands and larval control using kerosene and other petroleum products to suffocate the surface-breathing larvae. Within just a few seasons, saltmarsh mosquito numbers fell to a tolerable level, allowing summer outdoor activity to be pleasant again.

Coming back to the 21st century, Aedes sollicitans continues to be a challenging species to control along the Atlantic coast and the Gulf shore. Environmentally, complete marsh draining is generally not the best mosquito control measure due to the high value of coastal wetlands for many forms of wildlife, terrestrial and marine. Instead, open marsh water management techniques utilize ditches to connect shallow mosquito habitats to larger permanent waterbodies, eliminating standing water and giving natural predators such as fish access to mosquito larval habitats. Since the use of surface oils also destroys many non-target organisms, today bacterial larvicides are the pesticide of choice, often applied from the air over the larger, harder to access marsh areas.

We also now realize that the Eastern Saltmarsh Mosquito isn’t just a nuisance species. Aedes sollicitans is a competent vector of Eastern Equine Encephalitis (EEE) and dog heartworm, and both of these diseases are a serious concern throughout the species’ range. Today, the nuisance mosquito responsible for the beginnings of coordinated, large-scale, regional mosquito control programs in the USA is also targeted for its disease potential.

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) may be able to help.

Contact Us to Learn More About Effective Mosquito Management Strategies:

VDCI_Logo_squareSince 1992, Vector Disease Control International (VDCI) has taken pride in providing municipalities, mosquito abatement districts, industrial sites, planned communities, homeowners associations, and golf courses with the tools they need to run effective mosquito control programs. We are determined to protect the public health of the communities in which we operate. Our mosquito control professionals have over 100 years of combined experience in the field of public health, specifically vector disease control. We strive to provide the most effective and scientifically sound mosquito surveillance and control programs possible based on an Integrated Mosquito Management approach recommended by the American Mosquito Control Association (AMCA) and Centers for Disease Control and Prevention (CDC). VDCI is the only company in the country that can manage all aspects of an integrated mosquito management program, from surveillance to disease testing to aerial application in emergency situations.