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Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Diptera
Family:	Chironomidae
Genus:	Chironomus
Species:	C. Annularius
Binomial name
Chironomus Annularius (Linnaeus, 1758)

      Chironomus Annularius is a species of nonbiting midges that belong to the Chironomidae family and the Diptera Order. Even though they belong to the Chironomidae Family, this species is not recognized for their bloodsucking abilities but rather their similar appearances to relatives, the mosquitos (Diptera, Culicoidea). Annularius is found around the world, particularly in regions with bodies of fresh water. A few of the distinguishing features of the Annularius is the size of their chromosomes or their lack of a proboscis, a bloodsucking appendage.

Taxonomy

      The first documented accounts of the Chironomidae family was in the late 19th or early 20th century in England. Entomologist at first had trouble differentiating the difference subfamilies and genuses of the Chironomidae but had a breakthrough regarding the recognition of difference in their pupal stage. They decided upon the genus name Chironomus, which was derived from the Ancient Greek word cheironomos. The meaning of this word is to gesture with your hand. This followed the spirit of the family name Chironomidae, which in Ancient Greek means a pantomimist or one who entertains or dances with exaggerated hand movements. These meanings of names most likely alluded to the swarming behavior and movement of the midges belonging to the Chironomidae family. Lastly, the species name, Annularius, is derived from the Latin language, with the meaning 1 year old or annual. This naming is contradictory to the life span of the adult non-biting midges (3 Days to a few weeks) but may be related to the seasonable noticeability of the Annularius, particularly in spring and fall.

      Due to the broad distribution of the Chironomus genus across the world, there have been a plethora of nicknames given to it. Beginning off in North America, near Florida they are called chizzywinks or blind mosquitos and in the Great Lakes region they are referred to as bay flies or lake flies. Further north in Canada, the Chironomus are called muckle heads or muffle heads. Across the Atlantic in England, the Chironomus are referred to as non-biting midges or common midges. The diversity of name for such a genus of insects suggest that it exists almost worldwide.

Distribution and Habitat

Distribution

      C.annularius exist in almost every climate besides the harsh heat of some deserts. They tend to flourish in moist environments, particularly around bodies of fresh water. There have been notable sightings of their swarming behavior in the Great Lakes, in the swamps of Florida, in Lake Ijssel of Netherlands, and multiple lakes and rivers across England just to name a few. The male individuals of Chironomus Annularius are known for their swarming behavior for both physical fitness and reproductive fitness reasons. This swarming causes individuals of the Annularius to arrange themselves more densely in certain hotspots, increasing the population density around these select areas and decrease the population density elsewhere.

Habitat

General Habitat

      C.annularius, like many of its similar family members, gravitate towards habitats that have open bodies of fresh water and an abundance of plant life and decay. The exact specifications of these factors that go into selecting an optimal habitat for the Annularius is still very much unknown. However, research has been able to parse a few correlational factors and conditions.

Environmental Conditions

      Annularius prefer bodies of water with high populations of macrophytes. Macrophytes are known to not only provide a place where they give birth, but also provide an adequate supply of food as well as cover. The two most popular macrophyte species that the C.annularius are inclined towards would be the Potamogeton crispus and Potamogeton Lucens. Added on to this, the Annularius species stay on the outskirts of freshwater ecosystems in order to avoid areas of open water. By staying near vegetation and away from open water, Annularius decrease their chances of being attacked by predators. Environmental conditions that are still under research are vegetation height and flooding.

Factors

      The pH range of the water can extend between 6.0 nd 9.0. This is common for insects but prevents many aquatic vertebrate predators from living in the same water. Added on to this, Annularius are resistant to a certain degree to levels of salinity. They have been observed to survive in bodies of water with salinity ranges pushing 2-3 ppt. Lastly, oxygen levels can reach as low as 4% in bodies of water before it becomes a threat to the Annularius. Temperature also has a direct and indirect role on the survivability of Annularius. Temperature directly increase the development rate of the Annularius in egg and larvae phases, but also indirectly increases levels of food and resources.

Life Cycle

      The first stage of development is egg stage. Adult Annularius lay eggs directly into the fresh water. This egg will free float or sink to the bottom and hatch in a few days or at most a week. The most defining feature for the Annularius during this stage is not the egg itself, but rather the gelatinous matrix that accompanies the egg. This matrix expands in the water as it exits the womb and provides a protective layer for the eggs. Specifically, for the Annularius, the eggs are laid out in a helical arrangement in the matrix. The eggs themselves are 1-3 mm in diameter and an oval shape. They are produced in numbers averaging around 3,000.

      The second stage is the larval instar stage. There are 4 instar stages, ending with a preparatory pupal phase. During the instar phases, there are a series of great morphological change or additions with each molting. By the 4th instar stage, the following physical features have developed. The head capsule is a fully sclerotized cranium with very few internal structures excluding a few internal ridges. The mandibles are fully developed on an oblique plane, with a dominant apical tooth, a dorsal tooth, and an additional number of inner teeth. There are a set of eyes, or areas of pigment that lie beneath the cuticle and lastly two antennae protruding from the dorsal cranium. The body is segmented into 3 thoracic sections and 9 abdominal sections. Protruding from the thoracic sections are parapods, fleshy false legs that have claws at the end. Less noticeably, there are a set of procerci with a small set of apical hairs. At the end of the 4th instar stage, the 4th instar encases itself in a protective matrix for its pupal phase.

      The third stage is the pupal stage. This is considered the transitional phase between the 4th instar stage and the adult imago Annularius. This phase typically lasts between a few days and a week. The first notable development is the exuviae, a protective pupal skin. This can be segmented into the cephalothorax (Head and Thorax) and the abdomen. The cephalothorax has a thoracic horn, the main respiratory organ, and the leg sheath that cover the legs and fold back beneath the wings. The abdomen contains a distribution of spines, spinules, and tubercles. These have been described as having a Tergal pattern or as an aramament of some sort. At the end of the pupal stage, the pupae leaves its protective shell and swims upwards to the surface. Upon reaching the top of the water it molts one final time into the adult stage.

      The adult stage is the shortest lived and lasts only for a week. The Annularius are fully developed and have several distinct features. Their bodies are a dark brown or black color and the wing length ranges from 4 to 6 mm. The mandibles are still oblique but have grown to a much larger size and have a dark black hue. The spinules and spines protrude the most out of the back.

Morphology

      C.annularius has three defining characteristics in terms of physical structural. The first is the Johnston Organ, a sensory organ embedded in the Annularius’ antennae. This sensory organ is used to detect other individuals of the same species and possible mates. The range of detection is no more than cm. This small range requires Annularius to try mating on even the slightest hint that there’s a female nearby.

      The second difference is within species, and this a difference in size. There are larger male individuals and smaller male individuals within the C.annularius species. The larger males have higher longevity and can fly for more extended periods of time. This allows the larger individuals to search for food and resources and succeed more in physical fitness. The smaller males are at a disadvantage physically, but they can more easily latch onto females in the air to mate. Thus, the reproductive fitness of smaller individuals is higher. Male individuals of medium size don’t experience the benefits of either larger or smaller, and are thus weeded out or not present in the species.

      Lastly, there is a difference in wing spans and frequency of sound between males and females. This is due to inverse relationship between sound that the wing produces and wing length. For example, Annularius males have shorter wingspans, which causes them to produce higher frequency sounds (434±27.8). On the other hand, Annularius females have longer wingspans, which causes them to produce lower frequency sounds (240±17.2). This allows males to differentiate between other males and possible mates (females).

Social Behavior

      Swarming behavior or “aerial aggregations” is a common social behavior for C.annularius. There are costs and benefits to grouping with other members of your species. Individuals experience decreased rates of predation. This is due to an overall decline by predators on a swarm as well as the dilution of predator attacks per individual Annularius. Feeding has also been proven to be more efficient in larger populations. This may be due to group communication and direction to food and resources. Lastly, swarming of males increases the attraction of females, because the sound of the flight tone is amplified when the Annularius band together. This may not necessarily increase reproductive success of all individuals, but rather individuals that are able to detect and mate with females first experience the benefit of increased reproductive fitness.

Frequency (High vs. Low)

      As mentioned briefly above, the Annularius species have specific flight tone frequencies. Males have an average frequency of 434 Hz and females have an average frequency of 240 Hz. Different genuses of the Chironomus have different frequencies, thus the discernment of tonal frequencies is particularly important in swarming and for mating.

Diet

     Annularius, like most Diptera insects, differ in their diet through their life cycle. For example, in the egg stage, the egg is laid with all of the necessary nutrients and resources it needs to pass on to becoming a larvae. At the larval stage, the Annularius have developed mandibles and have varying internal teeth. These larvae feed on fine particulate organic material floating at the bottom of the body of water they were born in. This diet of decaying material continues with a brief intermission during the pupal phase, until adulthood. Once the Annularius emerge from their cocoons and out of the water, their diets changes dramatically. The most noticeable change is that the individuals no longer feeds on submerged organic particles. The Annularius no moves on to feed on surface algae, secretions of aphids, and other plant material. Even though the Annularius resemble their close relatives the mosquitos, the Annularius are non-biting midges and thus don’t partake in blood meals.

Human Interaction

Direct

      Multiple different species of the Chironomus genus are considered vectors of pathogens due to their blood sucking behavior. However, the Annularius belong to a subgroup that are referred to as non-biting midges. They’re meals are made up entirely of plant detritus and insect secretions. Thus, there is parasitism or infection from Annularius on humans or domestic animals.

Indirect

      The indirect effect of Annularius are still under research. However, the Annularius diet has been recognized as particularly influential. Annularius eat algae and macrophytes in fresh bodies of water. This can be beneficial when there are algae blooms or overcrowding of macrophyte beds. However, the opposite can be said when they pose a negative impact by clearing all healthy algae from ponds or affecting the health of macrophytes. Fortunately, most interactions of their observed diet have leaned more towards the former.

References

1. M. V. Fyodorova and A. I. Azovsky, Journal of Insect Behavior, Vol. 16, No. 2, March 2003, Interactions Between Swarming Chironomus annularius (Diptera: Chironomidae) Males:Role of Acoustic Behavior

2. Neems, R. M., Lazarus, J., and McLachlan, A. J. (1992). Swarming behavior in male chironomid midges: A cost-benefit analysis. Behav. Ecol. 3: 285–290.

3. Neems RM, Mclachlan AJ, Chambers R, 1990. Body size and lifetime mating success of male midges (Diptera: Chironomidae). Anim Behav 40:648-652.

4. MÓNIKA TÓTH, ARNOLD MÓRA, BÉLA KISS, GYÖRGY DÉVAI and ANDRÁS SPECZIÁR, Eur. J. Entomol. 109: 247–260, 2012, Are macrophyte-dwelling Chironomidae (Diptera) largely opportunistic in selecting plant species? ISSN 1210-5759 (print), 1802-8829 (online)

5. ARMITAGE P., CRANSTON P.S. & PINDER L.C.V. (eds) 1995: The Chironomidae. The Biology and Ecology of Non-biting Midges. Chapman & Hall, London, xii + 572 pp

6. Orel Zorina OV, Istomina AG, Kiknadze II, Zinchenko TD, Golovatyuk LV, Zootaxa. 2014 Jul 29, Redescription of larva, pupa and imago male of Chironomus (Chironomus) salinarius Kieffer from the saline rivers of the Lake Elton basin (Russia), its karyotype and ecology.

6. L. c. V. Pinder, Ann. Rev. Entornol. 1986.31:1-23 Copyright © 1986 by Annual Reviews Inc, BIOLOGY OF FRESHWATER CHIRONOMIDAE

7. OKSana (Zorina) V. Orel, Albina G. Istomina, Iya I. Kiknadze, Tatiana D. Zinchenko, Larisa V. Golovatyuk, Zootaxa Vol 3841, No. 4, Redescription of larva, pupa and imago male of Chironomus (Chironomus) salinarius Kieffer from the saline rivers of the Lake Elton basin (Russia), its karyotype and ecology

8. PINDER L.C.V. 1986: Biology of freshwater Chironomidae. Annu. Rev. Entomol. 31: 1–23.