Aedes triseriatus

Geographic Range

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 have not established populations overseas, eastern treehole mosquitoes do have the potential for range expansion. In 2001, a specimen was found in France in a shipment of used tires from the United States, but was immediately killed. With the prevalence of overseas travel and commerce, eastern treehole mosquitoes could certainly establish themselves in regions of Europe, if care is not taken.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Larvae of eastern treehole mosquitoes are aquatic, and live in water-filled cavities, typically in deciduous trees, giving the species their common name. Larvae can also be found in man-made containers that collect rain water, such as tubs, barrels, and abandoned tires. Adult females tend to oviposit in forested, shaded areas with dense under stories, generally avoiding open areas. Adults are terrestrial, and are usually found in forests, as well as suburban areas located near forests.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial
• freshwater freshwater

• Terrestrial Biomes
• forest forest

• Other Habitat Features
• suburban suburban

Physical Description

Eastern treehole mosquitoes are a medium-sized mosquito species. Females are generally larger, although the coloration is similar between the sexes. Their proboscis and their short palpi are black. The posterior of their head is covered in silver-white scales. Their thorax is brown or black, with a wide median stripe of dark brown, and their sides are white. Their scutellum is dark brown. Their abdomen is blue-black, with patches of white laterally. 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. Femora, tibia, and tarsi 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 posterior end. Eastern treehole mosquito larvae can be distinguished from related species by comb scales in double roles, anal papilla of unequal length, and multi-branched lateral hair on the anal saddle. Pupae are a similar color, with a shorter, curved body.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger

Development

Eastern treehole mosquitoes are holometabolous. Eggs overwinter on the sides of tree holes and other containers, and hatch in the spring when they are covered by water collected in the cavities, in response to the lack of oxygen. Water temperatures must be 4.1 to 12 degrees Celsius for eggs to begin hatching. Hatching is also influenced by a variety of other environmental factors, and the eggs usually do not all hatch at once. Hatchings occur in waves, which is useful in case of drought. If the tree hole dries up, the larvae will die, but eggs that have not yet hatched are still viable for when the tree hole fills with water again. Some eggs hatch after the first rainfall, while others do not hatch until there have been many rainfalls. Hatching can also be delayed if there is a high larval density already in the tree hole, or in response to older mosquito larvae in the water, which allows for newly hatched larvae to avoid competing for resources with older instars. Once the eggs hatch, there are four larval instars. Time of larval development depends on resource availability, with higher amounts of detritus allowing for faster development and larger adults. They then molt into pupae, and then eclose and leave the water as adults.

The development of eastern treehole mosquitoes has a high level of plasticity, and varies among regions and even from year to year. This is also due to delayed hatchings, amount of rainfall, temperature, and resource availability. As a result, there are usually multiple cohorts and all instar stages present at once. Some populations have been observed as univoltine, with one population per year. In these populations, larvae first appeared in mid-March, 2nd instars appeared in mid-April, with many first instars present. Four weeks later, all instar stages were present, with some pupae, and then adults present in June and July. Other populations have multiple generations per year. First instars first appeared in mid-April, and after 3 weeks, some 4th instar larvae were present. Pupae were present by the end of May. The first generation took about 6 weeks to develop into adults. In early June, a second generation occurred, resulting in pupae 2 to 3 weeks later. A third generation developed into 2nd instar larvae by early June, pupating within a week or two afterward. Development of the later generations took only about 3 weeks. Even small fourth generations have been observed, beginning in mid-August, though these might not have enough time to develop into adults before winter arrives. In some middle regions of their range, where the tree holes do not completely freeze, some larvae will diapause during the winter, in addition to overwintering eggs. In the most southern parts of their range, eastern treehole mosquitoes are active year round.

• Development - Life Cycle
• metamorphosis metamorphosis
• diapause diapause

Reproduction

Female eastern treehole mosquitoes must take a blood meal before mating, to mature a batch of eggs. Males find female mates by detecting the buzzing sound made by their beating wings, which is species specific. Mating typically occurs in the middle of the summer, from June to July, but due to the high plasticity of this species' development cycle, mating may also occur later in the season as later generations develop quickly and emerge as adults. In the southernmost region of their range, they mate year round. Typically, females only mate once, but some females live long enough to take a second blood meal and undergo a second oviposition cycle. In very rare circumstances, females live long enough to undergo a third cycle. Hybridizations have been recorded occurring between eastern treehole mosquitoes and other mosquito species, including Aedes hendersoni . Interestingly, females infected with La Crosse encephalitis virus, for which this species is a vector, are more efficient at mating than non-infected females. Infected females have an increased, earlier sperm transfer.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

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, along with several other factors. 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 that females are more likely to lay eggs in cavities that already have eggs in them. The presence of organic matter in the water is also possibly an appealing factor for females when searching for an oviposition site. Studies have also shown female eastern treehole mosquitoes are more attracted to dyed water. Oviposition rates are reportedly highest in July, though this varies by region, as the southernmost populations can breed year round. La Crosse encephalitis virus is transmitted vertically from parent to offspring. The virus overwinters in the eggs.

• Key Reproductive Features
• semelparous semelparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • internal internal
• oviparous oviparous

Adult eastern treehole mosquitoes provide provisioning in the eggs, as well as lay the eggs in suitable water-filled tree holes or other cavities. Otherwise, there is no more parental care.

• Parental Investment
• pre-hatching/birth
  • provisioning
    • female

Lifespan/Longevity

Females live anywhere from about 2 to 5 weeks after reaching adulthood. Males likely live for a shorter period of time.

Behavior

Adult eastern treehole mosquitoes are mainly crepuscular, with the females taking most of their blood meals during dawn and dusk. Males are active during this time, foraging for food, and searching for mates. Females infected with La Crosse virus show behavioral changes. When taking blood meals, infected females probe more and engorge less. This results in more feedings, resulting in more virus transmissions. Larvae can often be found floating near the water surface, with their breathing tubes sticking out of the water. Larvae are reasonably active, and move with a wriggling motion. They leave the surface to feed in the benthos and water column, and dart down to the bottom of the cavity when disturbed. Larval density can be very high in their tree holes. Studies have found anywhere from 60 larvae per 100 ml to 150 or more per 100 ml. 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.

• Key Behaviors
• flies
• crepuscular crepuscular
• parasite parasite
• motile motile
• sedentary sedentary
• social social

Home Range

Larval live in small tree holes and containers, which they do not leave until eclosion. Adults likely remain in the same general region from which they emerged.

Communication and Perception

The primary sensory structures for mosquitoes are their antennae, proboscis, and tip of their abdomen. Mosquitoes actively groom these sensilla, likely clearing them of obstructive particles. At the base of the antennae is an auditory organ. Males identify mates though sound, by detecting the wing beating tones of the females, which creates the buzzing sound that mosquitoes are known for producing in flight. This sound is species specific. When searching for blood meals, females typically detect chemicals and other cues to find hosts, such as carbon dioxide. They can also visually detect hosts, other mosquitoes, and the environment as a whole. Females use their proboscis to tactilely probe the skin of the host, and may reinsert the proboscis several times until they have found a suitable blood vessel. Light is also typically a strong attractant for mosquitoes, but some studies have reported that light traps are not particularly effective for catching eastern treehole mosquitoes. Larvae can also detect chemical signals, typically alarm signals, which would be produced by a neighboring larva when attacked or eaten by a predator.

• Communication Channels
• visual visual
• acoustic acoustic
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Adult mosquitoes are typically nectarivores. Males feed solely on nectar, while females take blood meals in addition to nectar. These acts of parasitism must occur before a female is able to mature her eggs and 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. Larvae of eastern treehole mosquitoes are detritivores. They filter feed and browse organic detritus from leaf litter, as well as microbes and particles of decaying invertebrates. Their feeding takes place primarily in the benthos and water column. Though there is some disagreement between researchers, cannibalism of earlier instars by older larvae may occur.

• Primary Diet
• herbivore herbivore
  • nectarivore nectarivore

• Animal Foods
• blood

• Other Foods
• detritus detritus
• microbes

• Foraging Behavior
• filter-feeding filter-feeding

Predation

The main predators of eastern treehole mosquito larvae are other larvae that co-habitate in their water-filled tree holes and cavities. 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 tree holes with eastern treehole mosquitoes. In some regions of the country, the larvae face little to no predation. In the presence of a predator, eastern treehole mosquito larvae decrease their activity, 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 eclosion, when they are weak and unsteady.

Ecosystem Roles

Eastern treehole mosquito larvae have a significant presence in tree hole communities, and are often the dominant species. They are often found in the same water-filled tree holes and cavities as other larval mosquito species, including Anopheles barberi , Orthopodomyia species, Toxorhynchites rutilus septentrionalis , and Aedes zoosophus . Eastern treehole mosquitoes also occur sympatrically with Aedes hendersoni , and hybridizations can occur between the two species. Larvae are often prey to predatory mosquito larvae inhabiting 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 has been much focus on the interactions of eastern treehole mosquitoes with other invasive tree hole mosquitoes. Larvae of Aedes albopictus , the Asian tiger mosquito, and Aedes japonicus , often live in the same tree holes. Aedes albopictus and A. japoncius seem to outcompete eastern treehole mosquitoes for resources, which has resulted in some declines in their population. Since Aedes albopictus can also vector the La Crosse encephalitis virus, this is unfortunately not helpful to humans and other virus hosts. However, eastern treehole mosquitoes seem to be able to still survive reasonably well in the same tree holes with these invasive species. Aedes albopictus appears to be more susceptible to predation and eastern treehole mosquitoes also overwinter more successfully as eggs, and emerges first, allowing them to colonize tree holes and utilize resources earlier than either of the invasive species, allowing them to co-exist.

Female eastern treehole mosquitoes are parasitic, and require blood meals before they can successfully reproduce. They typically feed on small mammals, such as chipmunks and squirrels, though they may also feed on birds and other larger mammals, including humans. Eastern treehole mosquitoes are the main vectors for the 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 transmit 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 .

• Ecosystem Impact
• parasite parasite

Economic Importance for Humans: Positive

Eastern treehole mosquitoes have provided a vast amount of research opportunities, as scientists study the tree hole communities, their interactions with and responses to invasive mosquito species, and their role as a vector for a large variety of both human and zoonotic diseases. Otherwise, eastern treehole mosquitoes have no positive effects on humans.

• Positive Impacts
• research and education

Economic Importance for Humans: Negative

Female eastern treehole mosquitoes are parasitic, and take blood meals from many small mammals, as well as humans. Their bites can be painful and very irritating. Eastern treehole mosquitoes are the main vectors of the 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 result in severe neuroinvasive disease, as well as 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 this number is likely underreported, as La Crosse virus can have no symptoms. In addition to La Crosse virus, eastern treehole mosquitoes can also vector 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.

• Negative Impacts
• injures humans
  • bites or stings
  • carries human disease
• causes or carries domestic animal disease causes or carries domestic animal disease

Conservation Status

Eastern treehole mosquitoes have no special conservation status. Since they can transmit many diseases to humans and other animals, efforts are directed towards control rather than conservation.

Other Comments

Aedes triseriatus is also known as Ochlerotatus triseriatus .

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Angela Miner (author), Animal Diversity Web Staff, Leila Siciliano Martina (editor), Texas State University.

References

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