The Asian tiger mosquito, Aedes albopictus, is a common mosquito in southern Ohio, but it can occur in all Ohio counties. The mosquito is native to Asia but was introduced to the United States in 1985, likely in imported, used tires (Sprenger and Wuithiranyagool 1986). The tires provided a site for egg laying and larval development. Subsequent trade of the tires spread the mosquito throughout the eastern and midwestern United States. Currently, the Asian tiger mosquito is considered one of the world’s most invasive species due to its ecological hardiness and aggressive nature that allows it to outcompete resident mosquito species. Due to the potential to vector many diseases through nuisance blood-feeding, the Asian tiger mosquito is an important pest in Ohio.
Mosquitoes are a type of fly with fragile, slender bodies and six long legs. They have one pair of wings covered in scales and a noticeable tube-like mouthpart called a proboscis. The size of the Asian tiger mosquito varies from 2–10 millimeters but averages around 6 millimeters. Males are morphologically similar to females but are approximately 20% smaller and have antennae that are feather-like. The name “tiger” is derived from the black body and legs with white stripes. A diagnostic characteristic is the dorsal white stripe down the top of the head and thorax. This characteristic can distinguish the Asian tiger mosquito from similar looking species in Ohio such the Eastern treehole mosquito, Aedes triseriatus, and the occasionally seen, but not yet established, yellow fever mosquito, Aedes aegypti.
Life Cycle and Habits
The adult female mosquito, like the male, feeds on nectar for daily energy needs. However, the female requires proteins and iron from blood to produce eggs. Female mosquitoes use specialized mouthparts to tap into host capillaries and suck blood while simultaneously releasing anticoagulants to maintain blood flow. These anticoagulants can cause a mild to severe irritation after feeding, leaving a red and itchy welt. Host finding is primarily accomplished through use of heat and carbon dioxide, but other olfactory cues and signals may be involved. This species uses a wide range of animals to take a blood meal, including humans, pets, wild mammals, and birds.
Female Asian tiger mosquitoes do not lay eggs directly in water like many other mosquito species. Instead, eggs are laid on the sides of or near water-holding containers. These mosquitoes also do not lay their eggs in areas of natural soil substrate, such as marshes, swamps, or flooded ditches. Eggs are laid in artificial habitats, such as flowerpots, and natural habitats, such as tree holes. This biology characterizes them as container breeders.
The Asian tiger mosquito has four life stages: egg, larva, pupa, and adult. Only adult females consume blood and transmit disease.
Four to five days after obtaining the blood necessary to produce eggs, the mosquito deposits them on the sides of water-holding containers. The eggs are one-half millimeter long, black or deep brown near time of hatching, and cigar-shaped. They are able to withstand desiccation up to a year and overwinter in temperate regions.
When containers holding eggs fill with water and temperatures are appropriate (60°F and above), the eggs are stimulated to hatch. This can occur as soon as 24 hours after eggs are laid. The larval stage is delicate as they require an aquatic environment to survive. They also are prone to predation or desiccation. Siphon tubes are used to obtain oxygen from the air, so larvae are found near the surface of the water. They exhibit a wriggling motion to swim and eat, so they are often termed “wrigglers.” The larvae filter feed on organic matter including bacteria and small amounts of decaying plant material in the water, and they live seven to ten days in this stage. The larvae are hairy, have distinctive brown heads and grow to approximately one eighth to one quarter inch in length before pupating.
The pupal stage is the transitory stage from aquatic larva to a terrestrial, free-flying adult. Pupae are small (about one-eighth inch long), brown, and comma-shaped. The pupae also breathe air through structures called trumpets and tumble when disturbed. This results in the term “tumblers.” This stage does not feed and remains in this stage for two to seven days depending on temperature.
The adult mosquito emerges from the pupal case and mates shortly after. Both male and female mosquitoes use the energy that they acquire from feeding on nectar from plants to fly and mate. Female mosquitoes take blood meals almost exclusively from mammals, including humans. Four to five days after laying eggs, females bite another vertebrate host, allowing them to transmit pathogens acquired from the first blood meal to subsequent humans or animals. The entire life cycle can occur in as little as seven days. The adult lifespan varies due to environmental conditions such as humidity, temperature, and predation, but they can live several days to one month.
The Asian tiger mosquito is active during the day. Feeding occurs mostly in the early morning to late afternoon (Illinois Department of Public Health, n.d.). Shady and cloudy conditions are preferable over direct sunlight. The adult female mosquito exhibits non-specific searching behavior until she senses a suitable animal. Females generally bite people on the legs, feet, and ankles. They are known to be aggressive, opportunistic, and persistent, often striking their target many times to get the blood meal required for reproduction (Centers for Disease Control and Prevention 2016). Many mammals are hosts, including humans, dogs, cats, squirrels, and even birds. The mosquito larvae can complete their developmental lifecycle in a one-half ounce of water, the size of the top of a 1-liter drink container. These behaviors make the Asian tiger mosquito hard to suppress.
The Asian tiger mosquito can survive in a wide range of climates and has spread rapidly since its introduction into the United States, as shown in Figure 6. Climate change can accelerate this process by creating more favorable habitats for the mosquito. Their native climate in Southeast Asia is hot and humid year-round, but the introduced populations originated from northern Japan and had the capacity to survive the winter as dormant or diapausing eggs. Hence, Asian tiger mosquitoes have adapted to overwintering in temperate climates in the United States. After emerging from the pupa, the adult mosquito generally does not travel more than one-half mile, although often adults travel less than 200 meters. The Asian tiger mosquito has been collected in over half of Ohio counties, mostly in southern Ohio as shown in Figure 7.
Importance as a Disease Vector
Mosquitoes are the most prominent vector for many public health diseases, but some locations of the world are more at risk than others and some diseases are species-specific. The Asian tiger mosquito has the potential to carry and transmit several viruses such as La Crosse encephalitis, Eastern equine encephalitis, St. Louis encephalitis, West Nile virus, Zika virus, Chikungunya, dengue, and microfilaria diseases such as canine heartworm (Armstrong et al. 2017). However, this does not mean that the Asian tiger mosquito is the most competent vector for these diseases or that they occur in high frequency in the United States or in Ohio. Currently, the Asian tiger mosquito is not considered a public health threat in the United States (Moore and Mitchell 2017). Diseases that may occur locally in Ohio include Eastern equine encephalitis virus, La Crosse encephalitis virus, St. Louis encephalitis virus, and West Nile virus. Other mosquito species in Ohio are more likely to transmit these viruses than the Asian tiger mosquito.
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