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Tuberolachnus salignus
Tuberolachnus salignus, or the giant willow aphid, is a species of aphid, in the genus Tuberolachnus. They are reputed to be the largest aphids, with a body length of up to 5.8mm.[1][2] First described by Johann Friedrich Gmelin in 1790, it feeds on many species of willow (Salix species), and has one known host-specific parasite, Pauesia salignae.[2] Tuberolachnus salignus does not require a male for reproduction. Only females have ever been recorded, which suggests that reproduction is parthenogenetic and all offspring produced are genetically identical clones.[3] DescriptionAdults exhibit a pear-shaped body with dark brown/grayish coloration.[4] This aphid species has distinct black dots that form rows along its body.[4] Along the dorsal side of their abdomen, about 2/3 of the way down, T. salignus displays a defining single large conical tubercle or bump that resembles a thorn which can grow to 0.2-0.3 mm.[5][6] Closer to the posterior and along the sides of the body are two smaller black cone structures (siphunculi).[4] Tuberolachnus salignus reproduces solely through parthenogenesis so all aphid adults are female.[5][7][8][9] Adults can be either winged or wingless.[4] The two pairs of wings are clear with a dark brown edge along the forewing.[4] When looking at T. salignus under a microscope the presence of numerous tiny hairs is apparent.[4][5] This gives the abdomen a grayish-gold hue.[4][5] Adult T. salignus has three pairs of legs that are primarily a dark brownish color, but smaller, red/orange sections are also present.[4][5] They also have a pair of antennae that are less than half of the aphid’s body length.[4][5] RangeNatural Global RangeTuberolachnus salignus is a cosmopolitan species.[7][10] They exist anywhere that willow species grow naturally or are cultivated.[7][10] The giant willow aphid originated in parts of Asia but has now spread to all parts of the globe (except Antarctica).[7][10] There is no known exact place of origin for this aphid species, but it is believed to be somewhere within Japan and Korea.[9][11] The only known parasitoid of this species is endemic to Japan, leading to the belief that this may be the place of their origin.[9][11] Tuberolachnus salignus is now found in all parts of New Zealand where willow species are present.[9][11] It only recently made it to New Zealand, with the first confirmed sighting in December of 2013 in Auckland.[9][11] HabitatThis species is almost entirely dependent on willow trees.[9][11] They live on the bark of these trees and feed on their sap.[9][11] These giant aphids survive year-round with the most activity being in late summer and early fall.[5][9][11] Their population numbers are known to be largely weather and temperature related.[12] Following instances of large amounts of rain, T. salignus populations have been known to increase rapidly.[3] EcologyLife Cycle/PhenologyTuberolachnus salignus has a generation period of 2–3 weeks, which is largely dependent on temperature.[6][3] Once hatched, the aphid larvae go through four stages of development until they reach their adult forms.[5][13] Ideal temperatures for T. salignus generation range from 17.5–22.5 degrees Celsius.[6] It takes two weeks for nymphs to become adults, with adults living an additional five weeks after that.[5] Mature aphids can produce anywhere from 35–71 offspring.[5][14][15] Generally, T. salignus is most active in the warmer months, with populations peaking in late summer and early autumn.[6][3] In colder months, the overall fecundity decreases but colonies are still active.[6][3] In the spring, colonies are usually not visible.[5][6][3] During this time, it is thought T. salignus retreats behind the willow tree bark or into the ground to escape the harsh climate.[5][6][3] Tuberolachnus salignus reproduces via parthenogenesis.[5][7][8][9] Resulting in a population consisting of all females.[5][7][8][9] All offspring are identical genetic clones of their mothers.[5][7][8][9] In turn, there are no mating behaviors that occupy these aphids as they do not participate in sexual reproduction.[5][7][8][9] Diet and ForagingTuberolachnus salignus is known to feed primarily on willow and Salix tree species such as the white willow (Salix alba), the common sallow (Salix cinerea')[16] and the Indian willow (Salix tetrasperma).[17] It has also been recorded on Quince (Cydonia oblonga),[18] Apple (Malus spp.)[18] and Poplar (Populus spp.)[18] Like many herbivorous Hemiptera, T. salignus uses modified mouthparts to pierce the phloem of plants and feed on its sap.[4][5] As the name suggests, giant willow aphids prefer willows of the Salix species but have been known to feed on poplar, apple, and pear species in New Zealand.[4][5] They prefer to feed during the day and during the warmer hours.[5] When feeding, the aphid will climb to the tip of the willow where the shoot begins.[4][5] The flesh of the plant is softer here, allowing the aphid to inject its stylets into the plant’s phloem.[4][5] Tuberolachnus salignus uses two stylets to extract the sap flowing within the phloem.[4][5] One is used to inject saliva into the phloem, while the other is used to ingest the sap and saliva mixture.[4][5] Willow sap is an extremely nutritious food source, as it provides critical sugars and water to various parts of the willow tree.[4][5] As the aphid feeds, it is ingesting an incredible amount of these sugars and water, so much so that it needs to excrete them to avoid overfeeding.[4][5][7][9] These are excreted as a sugary liquid known as honeydew, which attracts various other insect species such as honeybees, wasps, and ants.[4][5][7][9] These other species will feed on the honeydew that is excreted from T. salignus.[4][5][7][9] Predators, Prey, and ParasitesDue to the almost exclusive feeding of willow sap by T. salignus, the honeydew that is produced as a result attracts numerous types of insects.[4][5][7][9] Wasps, bees, ants, flies and coccinellids have all been observed to feed on honeydew of this species.[4][5][7][9] These insects feed only on the honeydew, not the actual aphid.[4][5][7][9] In New Zealand, Pauesia nigrovaria was introduced as a biocontrol parasitoid of T. salignus in 2020.[19] Elsewhere, like North America and parts of Europe, parasitic wasps, lady beetles, hover fly maggots, lace wings are frequent predators.[5] Interactions with HumansTuberolachnus salignus has only recently come into the limelight in New Zealand.[9][11] Upon arriving here in 2013, cause for alarm was immediately raised.[9][11] As previously noted, these giant aphids feed almost exclusively on willow species.[9][11] As T. salignus populations begin to rapidly grow on the willow tree, many negative impacts start to become apparent.[9][11] Willow trees are an important group of plants in New Zealand.[7][3] While they are not native, they are used in many facets of society in order to increase land stabilization and reduce soil erosion.[7][3] Historically, willows have been planted along riverbanks and on particularly sloping land to help keep the soil beneath from eroding away.[7][3] Furthermore, willows play an important roll in honey production throughout New Zealand.[7][3][20] The flowers of willows are rich with pollen and nectar and attract honeybees.[7][20] In other parts of the world, such as the U.K., large amounts of willows are cultivated for biomass production.[20] With the presence of large T. salignus colonies on willow trees, many of the contributions listed above are severely hindered.[7][3][20] Additionally, honeybees that forage on T. salignus honeydew have poorer health and produce a lower quantity and quality of honey.[7] References
Further reading
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