Eastern treehole mosquitoes are a medium-sized mosquito species. Females are generally larger, although the coloration is similar between males and females. Their proboscis and their short mouthparts are black. The back of their head is covered in silver-white scales. Their thorax is brown or black, with a wide stripe of dark brown down the middle, and the sides are white. Their abdomen is blue-black, with patches of white on the sides. Their wings are about 3.5 to 4.0 mm in length, with dark scales. Their hind femurs are yellowish-white, and dark towards the ends. The rest of their legs are all black. Larvae are long and thin, with segmented bodies, and are typically cream colored or brown. They have a breathing tube on their rear end. Pupae are a similar color, with a shorter, curved body. (Carpenter and La Casse, 1955; Costanzo, et al., 2011; Farajollahi and Price, 2013)
Eastern treehole mosquitoes (Aedes triseriatus) are the most common treehole mosquitoes in the United States. Native to the Nearctic region, they can be found in southern Canada and the eastern United States. Their range extends as far south as the Florida Keys, and west to Idaho, Utah, and Texas. In Canada, they are widespread in the southern parts of British Columbia, Quebec, Ontario, and Saskatchewan. While they do not have populations overseas, eastern treehole mosquitoes have the potential to survive in other regions. In 2001, a specimen was found in France in a shipment of used tires from the United States, but was immediately killed. With so much overseas travel and commerce taking place, eastern treehole mosquitoes could easily establish themselves in regions of Europe, if care is not taken. (Carpenter and La Casse, 1955; Farajollahi and Price, 2013; Medlock, et al., 2012)
Eastern treehole mosquito larvae are aquatic, and live in water-filled cavities, typically in deciduous trees, giving this species their name. Larvae can also be found in man-made containers that collect rain water, such as tubs, barrels, and abandoned tires. Adult females lay their eggs in forested, shaded areas with a lot of vegetation, generally avoiding open areas. Adults are terrestrial, and are usually found in forests, as well as suburban areas near forests. (Carpenter and La Casse, 1955; Ellis, 2008; Leisnham and Juliano, 2012)
Eastern treehole mosquitoes undergo complete metamorphosis, which includes egg, larva, pupa, and adult life stages. Eggs stay on the sides of tree holes and other containers during the winter, and hatch in the spring when they are covered by rain water collected in the holes. The eggs do not hatch all at once, but hatch in waves. Hatching in groups is useful in case of droughts. If the water in the tree hole dries up, then all of the larvae will die, but the eggs that have not hatched will be able to hatch the next time the tree hole fills with rain again. Some eggs hatch after the first rainfall, some hatch after many rain falls. Some eggs delay hatching if there are many larvae already in the tree hole, or if there are older larvae present. By waiting until there are less larvae present, there is less competition for food, which increases their chances of survival. Once the eggs hatch, there are four stages called instars. They then molt into pupae, and then leave the water as adults. The development cycle of eastern treehole mosquitoes is different depending on the region and the environmental conditions. In some regions, there is only one generation produced each year, with larvae hatching in mid-March, and adults appearing in June and July. In other areas, there are several generations each year, where the larvae take less time to develop to adulthood. These larvae become adults earlier in the season, and mate and lay eggs that have enough time before winter to hatch and also emerge as adults. In the middle part of the country, where the tree holes do not completely freeze, larvae can go into hibernation for the winter, along with the eggs. In the southernmost parts of their range, eastern treehole mosquitoes are active all year. (Carpenter and La Casse, 1955; Edgerly and Livdahl, 1992; Ellis, 2008; Harshaw, et al., 2007; Khatchikian, et al., 2009; Leisnham and Juliano, 2012; Williams, et al., 2007)
Female eastern treehole mosquitoes must take a blood meal before mating, to produce a batch of eggs. Males find female mates by detecting the buzzing sound made by their beating wings, which is unique to each species. Mating typically occurs in the middle of the summer, from June to July, but this is different in different regions. Mating may also take place later in the season as eggs laid later in the season develop and emerge as adults. In the southernmost regions, these mosquitoes mate year round. Typically, females only mate once, but some females live long enough to take a second blood meal and mate a second time. In very rare cases, females live long enough to mate a third time. Eastern treehole mosquitoes can mate with and produce offspring with different mosquito species such as Aedes hendersoni. Interestingly, females that are infected with La Crosse encephalitis virus, which this species carries and transfers to other animals, are more efficient at mating than non-infected females. (Farajollahi and Price, 2013; Frankino and Juliano, 1999; Gibson and Russell, 2006; Reese, et al., 2009; Spielman and D'Antonio, 2001)
After mating, eggs are laid on the side of water filled holes or other man-made containers. The eggs are laid singly or in groups of 2 to 5. They are laid just above the water line, and will not hatch until they have been covered with water of a certain temperature. Females typically only lay one batch of eggs, though some do survive long enough to mate a second time and lay a second batch. Studies have shown females are more likely to lay eggs in containers that already have eggs in them. The presence of leaf litter in the water is also possibly appealing for females when searching for a site to lay eggs. The rate of egg laying is reportedly highest in July, though this varies by region, as the southernmost populations can breed year round. La Crosse encephalitis virus is passed from parent to offspring, and the virus survives in the eggs over winter. (Beehler, et al., 1992; Carpenter and La Casse, 1955; Ellis, 2008; Reese, et al., 2009; Spielman and D'Antonio, 2001)
Adult eastern treehole mosquitoes provide nutrients in the eggs for the offspring to grow and develop. They also lay the eggs in a water-filled tree hole or other container in which the larvae can survive. Otherwise, they show no more parental care. (Carpenter and La Casse, 1955)
Females live anywhere from about 2 to 5 weeks after reaching adulthood. Males likely live for a shorter period of time. (Frankino and Juliano, 1999)
Adult eastern treehole mosquitoes are mainly active during dawn and dusk. During this time, females take most of their blood meals and males forage for food and search for mates. Females infected with La Crosse virus show behavioral changes. When taking blood meals, infected females probe more and ingest less blood. This results in more feedings, causing the virus to be transmitted to more animals. Larvae are often found floating near the water surface, with their breathing tubes sticking out of the water. Larvae are somewhat active, and move with a wriggling motion. They leave the surface to feed, and dart down to the bottom of the cavity when disturbed. Hundreds of larvae can be found in one small tree hole. Pupae tend to be much less active than larvae, and remain floating at the surface of the water. They can still sense a threat, however, and can move away when necessary. (Carpenter and La Casse, 1955; Reese, et al., 2009; Williams, et al., 2007)
Larval live in small tree holes and containers, which they do not leave until they reach adulthood. Adults likely remain in the same general region from which they lived as larvae. (Carpenter and La Casse, 1955)
The main sensory structures for mosquitoes are their antennae, proboscis, and tip of their abdomen. Mosquitoes actively groom these, likely clearing them of particles that may make them less functional. At the base of the antennae is a sound organ. Males identify mates through sound, by hearing the wing beating tones of the females, which creates the buzzing sound that mosquitoes are known for producing in flight. This sound is unique to each species, allowing males to find the right females. When searching for blood meals, females typically sense chemicals and other cues to find mammal hosts, such as carbon dioxide. They can also see hosts, other mosquitoes, and the environment. Females use their proboscis to probe the skin of the host, and may reinsert the proboscis several times until they have found a suitable blood vessel. Light may attract mosquitoes, but some studies have reported that light traps are not effective for attracting eastern treehole mosquitoes. Larvae can also detect chemical signals, typically alarm signals, which would be produced by nearby larvae when attacked or eaten by a predator. (Costanzo, et al., 2011; Gibson and Russell, 2006; Spielman and D'Antonio, 2001; Walker and Archer, 1988)
Adult mosquitoes eat nectar. Males feed only on nectar, while females take blood meals in addition to nectar. Taking blood must occur before a female is able to mate. Small mammals are the typical host of eastern treehole mosquitoes, particularly chipmunks and squirrels. They have also been observed feeding from birds, as well as larger mammals, including humans. Eastern treehole mosquito larvae eat decomposing leaves, microbes, and particles of decaying invertebrate bodies. They filter feed, and their feeding takes place primarily in the bottom and middle of the tree hole. Though there is some disagreement between researchers, cannibalism of young larvae by older larvae may occur. (Carpenter and La Casse, 1955; Ellis, 2008; Harshaw, et al., 2007; Koenekoop and Livdahl, 1986; Spielman and D'Antonio, 2001; Tuten, et al., 2012)
The main predators of eastern treehole mosquito larvae are other larvae that also live in the water-filled tree holes and containers. Larvae of the mosquitoes Toxorhynchites rutilus and Anopheles barberi, as well as larvae of the midge Corethrella appendiculata, are predatory and are often found in the same tree holes. In some regions of the country, eastern treehole mosquito larvae have no predators. In the presence of a predator, larvae decrease their activity in an attempt to not draw the attention of the predator, often by just resting at the surface. Predators of adults include ants, beetles, predatory hemipterans, bats, birds, and other opportunistic vertebrates. Adults are especially vulnerable to terrestrial predators shortly after they become adults, when they are weak and unsteady. (Alto, et al., 2009; Costanzo, et al., 2011; Ellis, 2008; Nannini and Juliano, 1998; Rochlin, et al., 2013; Spielman and D'Antonio, 2001)
Eastern treehole mosquitoes are an important part of tree hole communities, and are often the dominant species. They can be found in the same water-filled tree holes and containers as larvae of other mosquito species, including Anopheles barberi, Orthopodomyia species, Toxorhynchites rutilus septentrionalis, and Aedes zoosophus. They also live in the same area as Aedes hendersoni, and sometimes breed with them. Larvae are often prey to predatory mosquito larvae living in the same tree holes. Eastern treehole mosquito larvae can also be infected by parasitic gregarines, Ascogregarina barretti, which are found in the gut of the larvae, as well as in pupae and adults. There are invasive mosquito species that may move in to the same area as eastern treehole mosquitoes, and their larvae also live in the same tree holes. These invasive species include Asian tiger mosquitoes and Aedes japonicus. Asian tiger mosquitoes and Aedes japonicus use resources before eastern treehole mosquitoes can, causing the populations of eastern treehole mosquitoes to decline. However, eastern treehole mosquitoes are still able to co-exist in the tree hole habitats for a few reasons. Asian tiger mosquito larvae get eaten by predators more and eastern treehole mosquito eggs survive better during the winter. They also hatch earlier in the spring than the two invasive species, allowing eastern treehole mosquito larvae to use the resources first. (Alto, et al., 2009; Carpenter and La Casse, 1955; Farajollahi and Price, 2013; Leisnham and Juliano, 2012; Rochlin, et al., 2013)
Female eastern treehole mosquitoes are parasitic, and require blood meals before they can mate. They typically feed on small mammals, such as chipmunks and squirrels, though they have also been recorded feeding from birds and other larger mammals, including humans. Eastern treehole mosquitoes are the main vector for La Crosse encephalitis virus in the United States, and can transmit the disease to humans, as well as eastern chipmunks, gray squirrels, and red foxes. They also vector a large variety of other diseases to humans and many other domestic and non-domestic animals, including West Nile virus, eastern equine encephalitis, and Dirofilaria immitis. (Farajollahi and Price, 2013; Leisnham and Juliano, 2012; Reese, et al., 2009; Tuten, et al., 2012)
Female eastern treehole mosquitoes are parasitic, and take blood meals from many small mammals, as well as humans. Their bites can be painful and irritating. These mosquitoes are the main vector of La Crosse encephalitis virus in the United States. La Crosse encephalitis often has no symptoms, but can cause fever, headache, nausea, vomiting, and fatigue. Severe cases, which occur most often in children, can affect the nervous system, as well as cause encephalitis, which can cause seizures, coma, and paralysis. Long term disability or death can occur in very rare cases. There are about 80 to 100 cases in the United States each year, but the actual number of cases is likely higher, as La Crosse virus can have no symptoms. In addition to La Crosse virus, eastern treehole mosquitoes can also carry Cache Valley virus, eastern equine encephalitis, Highlands J virus, Jamestown Canyon virus, and West Nile virus. Additionally, they can also transmit Dirofilaria immitis, which causes heartworm in dogs, cats, and other animals. (CDC, 2009; Carpenter and La Casse, 1955; Farajollahi and Price, 2013)
Eastern treehole mosquitoes have provided many opportunities for researchers to study their tree hole communities, their interactions with invasive mosquito species, and how they transfer many diseases to both humans and other animals. Otherwise, eastern treehole mosquitoes have no positive effects on humans. (Farajollahi and Price, 2013)
Eastern treehole mosquitoes are not an endangered species. Since they can transmit many diseases to humans and other animals, researchers are more concerned with controlling and decreasing their population size, to prevent disease.
Angela Miner (author), Animal Diversity Web Staff, Leila Siciliano Martina (editor), Animal Diversity Web Staff.
Alto, B., B. Kesavaraju, S. Juliano, L. Lounibos. 2009. Stage-dependent predation on competitors: consequences for the outcome of a mosquito invasion. Journal of Animal Ecology, 78/5: 928-936.
CDC, 2009. "La Crosse Encephalitis" (On-line). Centers for Disease Control and Prevention. Accessed December 06, 2013 at http://www.cdc.gov/LAC/index.html.
Carpenter, S., W. La Casse. 1955. Mosquitoes of North America. Berkeley, California: University of California Press.
Costanzo, K., E. Muturi, B. Alto. 2011. Trait-mediated effects of predation across life-history stages in container mosquitoes. Ecological Entomology, 36/5: 605-615.
Edgerly, J., T. Livdahl. 1992. Density-Dependent Interactions Within a Complex Life Cycle: The Roles of Cohort Structure and Mode of Recruitment. Journal of Animal Ecology, 61/1: 139-150.
Ellis, A. 2008. Incorporating density dependence into the oviposition preference - offspring performance hypothesis. Journal of Animal Ecology, 77/2: 247-256.
Farajollahi, A., D. Price. 2013. A rapid identification guide for larvae of the most common North American container-inhabiting Aedes species of medical importance. Journal of the American Mosquito Control Association, 29/3: 203-221.
Frankino, W., S. Juliano. 1999. Costs of reproduction and geographic variation in the reproductive tactics of the mosquito Aedes triseriatus. Oecologia, 120/1: 59-68.
Gibson, G., I. Russell. 2006. Flying in tune: Sexual recognition in mosquitoes. Current Biology, 16/13: 1311-1316.
Harshaw, L., C. Crisawn, B. Kittinger, J. Carlson, G. Metz, L. Smith, C. Paradise. 2007. Decaying invertebrate carcasses increase growth of Aedes triseriatus (Diptera : Culicidae) when leaf litter resources are limiting. Journal of Medical Entomology, 44/4: 589-596.
Khatchikian, K., J. Dennehy, C. Vitek, T. Livdahl. 2009. Climate and Geographic Trends in Hatch Delay of the Treehole Mosquito, Aedes triseriatus Say (Diptera: Culicidae). Journal of Vector Ecology, 34/1: 119-128.
Koenekoop, R., T. Livdahl. 1986. Cannibalism among Aedes triseriatus larvae. Ecological Entomology, 11/1: 111-114.
Leisnham, P., S. Juliano. 2012. Impacts of Climate, Land Use, and Biological Invasion on the Ecology of Immature Aedes Mosquitoes: Implications for La Crosse Emergence. EcoHealth, 9/2: 217-228.
Medlock, J., K. Hansford, F. Schaffner, V. Versteirt, G. Hendrickx, H. Zeller, W. Bortel. 2012. A Review of the Invasive Mosquitoes in Europe: Ecology, Public Health Risks, and Control Options. Vector-borne and Zoonotic Diseases, 12/6: 435-447. Accessed December 06, 2013 at http://online.liebertpub.com/doi/pdfplus/10.1089/vbz.2011.0814.
Nannini, M., S. Juliano. 1998. Effects of the facultative predator Anopheles barberi on population performance of its prey Aedes triseriatus (Diptera Culicidae). Annals of the Entomological Society of America, 91/1: 33-42.
Reese, S., M. Beaty, E. Gabitzsch, C. Blair, B. Beaty. 2009. Aedes triseriatus Females Transovarially Infected With La Crosse Virus Mate More Efficiently Than Uninfected Mosquitoes. Journal of Medical Entomology, 46/5: 1152-1158.
Rochlin, I., R. Gaugler, E. Williges, A. Farajollahi. 2013. The rise of the invasives and decline of the natives: insights revealed from adult populations of container-inhabiting Aedes mosquitoes (Diptera: Culicidae) in temperate North America. Biological Invasions, 15/5: 991-1003.
Spielman, A., M. D'Antonio. 2001. Mosquito. New York, New York: Hyperion.
Tuten, H., W. Bridges, K. Paul, P. Adler. 2012. Blood-feeding ecology of mosquitoes in zoos. Medical and Veterinary Entomology, 26: 407-416.
Walker, E., W. Archer. 1988. Sequential organization of grooming behaviors of the mosquito Aedes triseriatus. Journal of Insect Behavior, 1/1: 97-110.
Williams, D., S. MacKay, R. Verdonschot, P. Tacchino. 2007. Natural and manipulated populations of the treehole mosquito, Ochlerotatus triseriatus, at its northernmost range limit in southern Ontario, Canada. Journal of Vector Ecology, 32/2: 328-335.