Aedes taeniorhynchus, or the black salt marsh mosquito, is a mosquito in the family Culicidae. It is a carrier for encephalitic viruses including Venezuelan equine encephalitis and can transmit Dirofilaria immitis. It resides in the Americas and is known to bite mammals, reptiles, and birds. Like other mosquitoes, Ae. taeniorhynchus adults survive on a combination diet of blood and sugar, with females generally requiring a blood meal before laying eggs.
This mosquito has been studied to investigate its development, physiological markers, and behavioral patterns, including periodic cycles for biting, flight, and swarming. This species is noted for developing in periodic cycles, with high sensitivity to light and flight patterns that result in specific wingbeat frequencies that allow for both species detection and sex distinction.
Ae. taeniorhynchus is known to be a pest to humans and mechanisms for controlling Ae. taeniorhynchus populations have been developed. The United States has spent millions of dollars to control and contain Ae. taeniorhynchus.
Taxonomy German entomologist Christian Rudolph Wilhelm Wiedemann described Ae. (Ochlerotatus) taeniorhynchus in 1821. Alternate namings for the species include Culex taeniorhynchus (Wiedemann, 1821), Ochlerotatus taeniorhynchus (Wiedemann, 1821), and Culex damnosus (Say 1823).
Aedes niger, also known as Aedes portoricensis, is a subspecies of Ae. taeniorhynchus. It can be identified by its last posterior tarsal joint, which is mostly black rather than banded in white. It resides in Florida and can migrate as far as .
Analysis of microsatellite data on the genes of Ae. taeniorhynchus living in the Galapagos Islands show genetic differentiation between coastal and highland mosquito populations. Data indicates minimal gene flow between the populations that only occurs during periods of heightened rainfall. Genetic differences suggest that habitat differences led to driving adaptation and divergence in the species, eventually leading to future speciation. Highland mosquitoes have population features characteristic of a founder effect due to low genetic diversity manifesting as low heterozygosity and low allelic richness, which may have resulted from egg dormancy during periods of dryness.
Description
Ae. taeniorhynchus adults are mostly black with areas of white banding. A single white band appears at the center of the proboscis, multiple white bands span the distal ends of the legs following the leg joints, and the last hind leg joints are completely colored white. Ae. taeniorhynchus wings are long and narrow with scaled wing veins. Experimental investigation of evolutionary coloration of Ae. taeniorhynchus yielded negative results. Mosquitoes reared in conditions of darkness, backgrounds colored black, white, or green, and lighting conditions of fluorescent light or sunlight, showed no color changes in the fat body nor in the head capsule, saddle, or siphon. This lack of cryptic coloring is suggested to be due to a lack of threat to the species; because the species habitat is a temporary water source used for larval growth, this temporary environment has few predators and relatively little danger.
Males and females can be distinguished based on their antennae: males have plumose (feather-like) antennae while females antennae are sparsely haired.
Noise detection Ae. taeniorhynchus swarms can be detected through sound. Noises with frequencies between 0.3 and 3.4 kHz at sound level 21 dB are detectable across 10–50 m in distance. An individual mosquito can be heard across 2–5 cm in distance when sound level rises to 22-25 dB. Male and female mosquitoes can also be distinguished by their wingbeat frequencies, which are 700–800 Hz for males and 400–500 Hz for females. As a result, flight sounds are used to determine flight activity and distinguish sex of groups.
Microbiome Aedes mosquitoes have a characteristic microbiome that modulate the effects of diet. Microbiome makeup is reported to differ between males and females in Aedes mosquitoes, such as Aedes albopictus and Aedes aegypti. Namely, in Aedes albopictus, males feed on nectar to acquire Actinomycetota while females contain Pseudomonadota (such as Enterobacteriaceae) that mediate levels of redox stress caused by feeding on blood-meals.
Similar species
The main physical distinctions between Ae. taeniorhynchus and other species come from the white banding that covers several body parts along Ae. taeniorhynchus. The species, like other Aedes mosquitoes, exhibits basal banding of the abdomen, but Ae. taeniorhynchus also uniquely exhibits white-tipped palps and a central white ring on the proboscis.
This species looks similar to Aedes sollicitans, except for subtle differences in the larval and adult stages. In the larval stage, Ae. taeniorhynchus has a shorter breathing tube, its scale patches are rounded instead of pointed at the tips, and spines that line the edges of each scale patch are smaller near the scale patch base. In the adult stage, Ae. taeniorhynchus is smaller and mostly black while Ae. sollicitans is golden brown.
The species also bears similarity to Aedes jacobinae, which falls within the Taeniorhynchus subgenus due to its particular hypopygium structure, but it is considered a distinct species because it does not have leg markings. Similarly, this species can also be distinguished from Aedes albopictus, commonly known as the Asian Tiger Mosquito, as Ae. taeniorhynchus, unlike Ae. albopictus, does not have markings on its back.
Distribution Ae. taeniorhynchus is widely distributed across North and South America, though more highly concentrated in southern regions. At the time of the fly's initial discovery the species resided in coastal regions, and then gradually moved towards the interior of the Americas. Gene flow analysis derived from microsatellite data indicated that mosquitoes located in the Galapagos Island in the Pacific Island frequently migrate between islands on an isolation by distance basis. Incidence of ports was a strong factor contributing to migration, suggesting human-aided transport contributed to inter-island migration.
Habitat
Ae. taeniorhynchus resides in habitats with a temporary water source, making mangrove and salt marshes or other areas with moist soil popular locations for egg laying and immature growth. These habitats are highly variable but often have high salinity with an observed soluble salt content in soil of at least 1644 ppm.
In the case of environmental conditions of dryness and low temperatures which are unfavorable for egg hatching, eggs can remain dormant for years. Factors controlling the scale of A. taeniorhynchus growth during pre-emergence depend on environmental conditions matching moisture level and temperature. In Southern Florida, the main factors are tide height and amount of rainfall, while sites in California rely on tide height alone. In Virginia, these factors are limited to levels of rainfall and temperature. Generally favorable factors can turn negative at extreme values, causing survival rate to decline. Excess water washes mosquito eggs away and extremely high temperatures can lead to water source evaporation.
This species exhibits sensitivity to temperature, with differences found for constant, split, and alternating temperatures. At constant temperatures of 22, 27, and 32 °C, life span increased with temperature, but at split temperatures, mosquitoes were also split between life and death. At different temperatures, the rate of aging was independent in males, but higher for females living at 22 and 27 °C. At alternating temperatures, life spans were temperature independent for all sexes and temperatures, except for favoring of alternation between 22 and 27 °C by females.
Breeding locations for Ae. taeniorhynchus are often in contact with vegetation such as Distichlis spicata (spike grass) and Spartina patens (salt meadow hay) in grass salt marshes and Batis maritima (saltwort) and species from the Salicornia genus (glassworts) in mangroves. This species of mosquito is found in close proximity to other mosquitoes that reside in marches. These include Aedes sollicitans (eastern salt marsh mosquito), Anopheles bradleyi, and A. atropos.
Life history According to observational field studies, Ae. taeniorhynchus carries out several behavioral trends at different stages of life. Growth and pupation of this species were found to be affected by environmental factors of nutrition, population density, salinity, light-dark, and temperature.
Eggs Females lay eggs on dry ground, and egg hatching is triggered by the presence of water, such as rain or flooding. Egg laying yield from females, an indicator of fecundity, differs based on diet: in populations of low autogeny, rare autogenous females each laid less than 30 eggs, while egg yield was significantly higher in populations with majority autogenous females. Eggs laid in the right temperature and humidity conditions undergo embryogenesis, then stay dormant until hatching.
Larval in-stars Upon hatching, the species progresses through 4 larval instars: the first 3 instars are affected primarily by temperature, with minor effects by salinity; the fourth instar is affected by all environmental factors. In the fourth instar, increased food sped up development time while crowding and salinity stunted growth.
Preferred temperature for all 4 instars is between 30 °C and 38 °C but average preferred temperature increases with age. The first instar prefers an average temperature of 31.8 °C and the early fourth instar prefers a temperature of 34.6°. The late fourth instar, however, has a lower preferred temperature than the early fourth instar, at 33.0°. Starved larvae were found to have a wider preferred temperature range that is centered around lower temperatures. Laboratory larval colonies cultured for years 27.0 °C were found to prefer consistently lower temperatures.
Fourth-instar larvae were noted to drink sea water (100 nL/h) and secrete hyperosmotic fluid through the rectum. This fluid is similar to seawater but with 18-fold higher potassium levels. Because the secreted fluid does not allow for osmotic balance with the ingested fluid, studies suggest that the anal papillae aid in salt secretion.
Pupa All environmental factors affect pupation regarding the insect's diurnal rhythm, which has a period of 21.5 hours. Factors leading to an increased pupa period include erase of light-dark cycles with all dark or all light conditions, increased salinity, and crowding. These trends continued to adhere to a preference for temperatures close to 27 °C or 32 °C. Pupa also exhibit differential aggregation formation due to these environmental factors. Cluster type aggregations form alongside temporary crowding and excess of food while ball type aggregations may manifest out of temporary crowding but lack of food. At lower constant temperatures of 22 °C and 25 °C, cluster type aggregations may form but higher temperatures of 30° and 32 °C inhibit aggregation formation. Aggregations produced pupa with slightly heavier dry body weights and promoted developmental synchronization in ecdysis and greater likelihood of migration at emergence.
Adult stages Males and females mosquitoes emerge from their egg sites in similar ways. They remain in their sources of water for 12–24 hours. Adults then migrate away from the egg laying ground over the course of 1–4 days. Different sexes exhibit differential migration, with most females traveling at least , and most males traveling no farther than . Female migration follows a random pattern with no limitation on migration direction and migration occurring along a 5-day cycle. Males initially travel with females until they hit a stopping point, where they replace migration with swarming.