Chionea

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Chionea
Chionea sp. - MUSE.jpg
Chionea sp. Reconstrution - scale 20:1. (MUSE - Science Museum, Trento)
Scientific classification
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Chionea

Dalman, 1816
Type species
Chionea araneoides
Dalman, 1816
Species

see text.

Diversity
ca. 40 species

Chionea is a genus of wingless limoniid crane flies. It consists of two subgenera, the holarctic Chionea and palaearctic Sphaeconophilus. About 40 species are currently recognized in the northern hemisphere, but there are probably several undescribed species. They are commonly called snow flies.

Description[edit]

Adults occur during winter, where they can be observed walking over snow. They produce glycerol in their hemolymph, preventing them from freezing.[1]

Up to 200 eggs have been found in female snow flies, which are laid singly.[1] The larvae occur under decaying leaves in wooded regions (Marchand, 1917). At least the larvae of some species seem to feed on feces in rodent burrows.[1]

Adults seem to actively seek out the coldest place they can find and drink water by pressing their proboscis against the snow (Marchand, 1917), but are not known to feed. Adult snow flies live for up to two months. They can walk at a speed of about 1,30 m per minute, and at least males have been observed to leap, without being provoked.[1]

Male C. alexandriana are about seven millimeters long.

They are easiest found on snowbanks in the afternoon, in areas that are to some extent forested. Some species have been found to be abundant on the floor of caves.[1]

The winglessness of the genus is probably attributable to the fact that at sub-freezing temperatures, it is very hard to generate enough energy for maintaining flight muscles. Also, the space normally taken by flight muscles is used to store eggs. However, the halteres have not been reduced and are innervated, thus probably serving as sensory organs.[1]

Cold Tolerance[edit]

As some species of Chionea are adapted to living on snow and in subnivean habitats[1][2], they are considered cold tolerant insects. It has been frequently reported that Chionea are observed at temperatures between 0 and -6°C[2]. In an experiment conducted in a laboratory environment, Chionea araneoides specimens died at a mean temperature of -7.5°C, their supercooling point[3]; another experiment on an undetermined species of European Chionea demonstrated a supercooling point of -11.2°C[4]. The antifreeze agent found in Chionea hemolymph has been determined to be sugar trehalose[4].

Reproduction[edit]

Mating is indiscriminate (probably because it is very hard to find a specimen of the other sex for them) and takes 30 to 70 minutes. While winged crane flies face in opposite directions, snow flies position themselves similar to many beetles, thereby requiring the male copulatory organs to be inverted 180 degrees.[1]

Predators[edit]

One of the reasons why adults emerge in winter seems to be the absence of predators. However, "rock crickets" (Grylloblattidae) have been shown to feed on them. Because the cysticercoid form of a tapeworm species has been found in two out of three C. stoneana specimens in eastern Kansas, they also have to be eaten by mice, which are the tapeworm's host. The snow fly larvae likely take up these tapeworms via mouse feces.[5]

A high magnification dorsal view of a snow fly specimen with a nematode dauer placed around the snow fly's cervix ("neck").

Parasites[edit]

Tapeworm cysticercoids, possibly of the genus Hymenolepis, have been found in the abdomens of Chionea stoneana.[1]

While most likely not a parasite of snow flies, a species of nematode, similar to Rhabditis, can sometimes be found in a ringed capsule, which is called a (dauer), around the neck of adult snow flies.[1] Immature nematodes develop inside the dauer before ultimately dispersing from it.[1][5] It has been speculated that the female nematode lays this ring around the fly's neck when it emerges from the pupa and cannot yet move properly. These nematodes are presumed to be phoretic, meaning that they use the snow fly as a mechanism for dispersal, and not snow fly parasites.[1]

Species[edit]

This list was adapted from the Catalogue of the Craneflies of the World (January 2007).

Subgenus Chionea (Holarctic)

Subgenus Sphaeconophilus (Palaearctic)

References[edit]

  1. ^ a b c d e f g h i j k Byers, G. (1983). "Crane fly genus Chionea in North America". The University of Kansas Science Bulletin. 52 (6): 59–195.
  2. ^ a b Hagvar, Sigmund (1971). "Field observations on the ecology of a snow insect, Chionea araneoides Dalm.(Diptera, Tipulidae)". Norsk Entomol Tidsskr – via http://www.entomologi.no/journals/nje/old/V18/NET_18_01_1971.pdf#page=35.
  3. ^ Somme, Lauritz; Ostbye, Eivind (1969). "Cold-Hardiness in Some Winter Active Insects" (PDF). Norsk ent. Tidsskr. 16: 45–48.
  4. ^ a b Vanin, S; Bubacco, L; Beltramini, M (2008). "Seasonal variation of trehalose and glycerol concentrations in winter snow-active insects". Cryoletters. 29: 485–491.
  5. ^ a b Schrock, J. R. (1992). "Snow flies". Emporia State University.

Further reading[edit]

External links[edit]

See also[edit]