Gyrostigma
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Gyrostigma is a genus of the warble flies counted gasterophilinae . The larvae of the Gyrostigma species parasitize in the stomach of rhinos .
features
They are large flies with a body length of 24 to 35 millimeters ( Gyrostigma rhinocerontis ) or 20 to 24 millimeters ( Gyrostigma conjungens ), with noticeably long, slender legs. Gyrostigma rhinocerontis is predominantly black in color, with smoky black darkened wings. The head with the antennae, a variably shaped central stripe on the trunk, from the head to the tip of the scutellum (which can very rarely be missing), the legs and usually also the tip of the abdomen, is colored reddish orange. Gyrostigma conjungens is yellow to reddish brown in color, without any differently colored median stripes on the trunk.
Diagnostic features for the genus are: The ocelles are completely absent. The horseshoe-shaped ptilinal suture is clearly visible on the head. As is typical for flies, the antenna consists of three segments, in the genus the antenna bristle (Arista) is bare and the second antenna segment is noticeably large and deeply split and enclose the smaller third segment between itself, its dorsal part covers the segment when viewed from above . There are long and deep antenna pits that are divided by a central keel. The mouthparts are rudimentary and inoperable, two buttons (palps) can be seen next to the remains of the trunk. The postscutellum (a section of the trunk) is missing from the trunk. No adhesive pads ( pulvilli ) are formed on the phalanx .
The larvae reach up to 40 millimeters in length. They are predominantly white to yellowish, the early stages pale pink in color. The body consists of 11 segments, the boundary of the first two being difficult to see. The third to eleventh segment has three to four rows of protruding thorns at the rear end, with those in the first row being the longest. On the fifth to eighth segment there is also a field with around five additional thorns. The shape of the stigma plate (peritrema) at the rear end of the larvae is decisive.
Way of life
Females of Gyrostigma lay their eggs on the skin of their host in the head area, according to some data they are said to prefer the area around the horns. The first instar larvae presumably enter the host via the mouth or nostrils (this process has never been observed and is unknown in detail). As soon as they reach the stomach, they anchor themselves in the stomach wall. In addition to the hook-like mouthparts, the thorns pronounced on all segments help them. When detached, the larvae leave deep pits in the stomach wall, which, however, do not scar. The damage to the rhinoceros host is therefore rated as rather low. In the stomach of a single rhinoceros there are often very numerous, sometimes many hundreds, larvae. The larvae go through three larval stages in which they increase greatly in size. A rather slow growth rate is assumed, but this has not been proven by direct observations. Mature larvae of the third stage that are mature to pupation detach from the stomach wall and are excreted from the anus with the feces. The black-colored pupae cannot be found in the excrement piles of the species; the larvae evidently leave them to pupate aside. The adults hatch after six weeks of pupal rest. Almost nothing is known about the way of life of the imaginal flies, they are mainly known from specimens bred in the laboratory from the larvae. Imagines of Gyrostigma sumatrensis are completely unknown. Since the animals have no functional mouthparts, they probably only live for a short time, a few days. They also seem to be nocturnal. Ultimately, the lack of observations is probably due to the fact that not many entomologists want to approach a living rhinoceros to look for the flies.
While Gyrostigma rhinocerontis has two generations per year (March to April and October to December), the sparse reports of Gyrostigma conjungens indicate only one generation.
The larvae of the species were accidentally imported into European zoos by rhinos from South Africa that were caught in the wild. As far as is known, they do not pose a health risk to the rhinos. Treatment is therefore considered unnecessary.
Phylogeny, taxonomy, systematics
The genus Gyrostigma is one of three genera of the Gastendasseln (Gasterophilinae). According to genetic and morphological data, the closest related and sister group is the genus Gasterophilus , which occurs in the stomach of horses.
The genus includes only three species:
- Gyrostigma rhinocerontis Owen , 1830. The best known species. The larvae grow in the stomach of the black rhinoceros or square-lipped rhinoceros approach. The rhinoceros dassel fly is the largest African fly.
- Gyrostigma conjungens Enderlein , 1901. Larvae of the species were discovered in the stomach of a black rhinoceros that was shot on Kilimanjaro in Tanzania. In 1961, larvae were isolated from a rhinoceros from the Tsavo East National Park and then moved to the imago. No specimen has been observed since then.
- Gyrostigma sumatrensis Brauer, 1884. The species is only known from larvae found on the Sumatran rhinoceros in 1884 . The finds go back to dead animals in the zoos of Hamburg and Leipzig.
The species are considered threatened because they only live on rhinos that are themselves threatened with extinction. It is possible that other species exist but have not yet been described. It is also possible that some species are already extinct as the number of rhinos is steadily decreasing.
literature
- Barraclough, David A. "Bushels of Bots". Africa's largest fly is getting a reprieve from extinction. In Natural History 115 (5): June 18-21, 2006. online at archive.org
- Fritz Zumpt (1965): Animal Parasites of the Rhinos. Nature and Museum 95 (5): 191-206.
Individual evidence
- ^ F. Zumpt (1962): The Genus Gyrostigma Brauer (Diptera, Gasterophilidae). Journal of Parasitics 22: 245-260.
- ↑ David A. Barraclough: "Bushels of Bots". Africa's largest fly is getting a reprieve from extinction. In Natural History 115 (5): June 18-21, 2006. online at archive.org
- ↑ a b c T. Pape: Phylogeny and Evolution of Bot Flies. Chapter 3 in Douglas D. Colwell, Martin JR Hall, Philip J. Schol (editors): The Oestrid Flies: Biology, Host-parasite Relationships, Impact and Management. CABI Publishing, Wallingford, 2006. ISBN 978-0-85199-684-4 .
- ↑ Liping Yan, Thomas Pape, Mark A. Elgar, Yunyun Gao, Dong Zhang (2019): Evolutionary history of stomach bot flies in the light of mitogenomics. Phylogenomics Virtual Issue (9th Dresden Meeting Insect Phylogeny, September 20-22, 2019). doi: 10.1111 / syen.12356 (open access)
- ^ Douglas D. Colwell, Domenico Otranto, Jamie R. Stevens (2009): Oestrid flies: eradication and extinction versus biodiversity. Trends in Parasitology 25 (11): 500-504. doi: 10.1016 / j.pt.2009.07.011
Web links
- Rhino Resource Center , with an extensive bibliography, also on rhinoceros parasites.