Taxonomic review of Gasterophilus (Oestridae, Gasterophilinae) of the world, with updated nomenclature, keys, biological notes, and distributions

Abstract A taxonomic review of Gasterophilus is presented, with nine valid species, 51 synonyms and misspellings for the genus and the species, updated diagnoses, worldwide distributions, and a summary of biological information for all species. Identification keys for adults and eggs are elaborated, based on a series of new diagnostic features and supported by high resolution photographs for adults. The genus is shown to have its highest species richness in China and South Africa, with seven species recorded, followed by Mongolia, Senegal, and Ukraine, with six species recorded.


Introduction
The oestrids or bot flies (Oestridae) are known as obligate parasites of mammals in their larval stage. They are often highly host specific, and the short-lived, non-feeding adult flies may show remarkable patterns of camouflage or mimicry (Zumpt 1965; Photographs are provided for G. intestinalis (De Geer), G. meridionalis, G. nasalis (Linnaeus), G. nigricornis, G. ternicinctus, and G. pecorum. High resolution photographs of G. flavipes, G. haemorrhoidalis and G. inermis (Brauer) were recently provided by Li et al. (2019).
Morphological terminology follows Cumming and Wood (2009) for adults and Ferrar (1987) for eggs.

Distribution
A worldwide species diversity map was produced using the non-commercial version of StatPlanet (StatSilk 2018).

Format of catalog
Regional catalogues (Pont 1973(Pont , 1980Soós and Minář 1986) are followed with regard to synonyms as the valid names for species of Gasterophilus are accepted throughout current literature and the synonymies appear stable. All original proposals of available and unavailable names and first occurrences of misspellings were checked and updated for information on type locality. Generic synonyms are given with author, year: page, type species and mode of designation. The most important taxonomic, morphological, biological, distributional and evolutionary studies of Gasterophilus are selected and listed chronologically.
Valid species are treated in alphabetic order, with the valid name given in bold followed by a list of all synonyms in their original generic combination with author, year and page plus type locality given in modern English (with an original quotation where considered relevant, e.g., France, Pyrenees, "Dans les Pyrénées"). Precise localities provided by early authors are cited as well [e.g. Democratic Republic of the Congo (as "Zaire"), 11.5 km W of Luapula river (as "6 milles W. du Luapula")]. Synonyms are listed chronologically for each species, followed by all published misspellings known to us. Most important references about taxonomic, morphological, biological, distributional and evolutionary studies of species in Gasterophilus are selected and listed chronologically.
Biological information provided for eggs, larvae and adults is summarized and presented in Table 1.
The generic diagnosis is provided for adults, eggs and larvae, while species diagnoses are provided only for adults. Keys are modified from already existing keys and updated with more diagnostic characters for both adults and eggs. Comprehensive identification keys to first instar larvae were published by Grunin (1969) and Zumpt (1965), and to third instar larvae by Li et al. (2018).
Hosts. Known exclusively from the genus Equus Linnaeus (Perissodactyla: Equidae). So far, no records have been made from the species E. grevyi Oustalet (Grévy's zebra) and E. kiang Moorcroft (kiang or Tibetan wild ass).
Distribution and diversity. Native distribution matches that of the horse family, currently with highest diversity in China and South Africa, with 7 species recorded, followed by Mongolia, Senegal and Ukraine, with 6 species recorded (Fig. 19). Introduced with domestic hosts to most parts of the world. Key to adults of Gasterophilus spp.

1
Wing with darkened patches (Fig. 10C Antennal pedicel elongated, length/width ratio more than 0.8 (Figs 3F, 9F); facial plate setose; abdomen ground color yellow in male (Fig. 3D), mainly black in female (Fig. 9E); female terminalia short (Fig. 9E), abdominal sternite 8 with a keel-shaped apex (Fig. 16F)  Hind trochanter ventrally with a spatulate process in male or a tubercle in female (Grunin 1969: fig. 95); male surstylus yellow, with a black apex (  Table 1 Oestrus flavipes Olivier, 1811: 467. Type locality: France, Pyrenees ("Dans les Pyrénées"). Diagnosis. Facial plate bare. Postsutural scutum of light color (yellowish), with rectangular area near scutoscutellar suture. Wing completely hyaline. Distance between crossveins r-m and dm-cu at least twice as long as r-m. Meron with unmodified setae. Legs yellow; hind tarsus with long, strong and dense setae ventrolaterally. Abdomen ground color yellow. Male cercus short and broad, length/width ratio equal or less than 1.0; surstylus yellow, gradually tapered proximally and distally, with a gradually tapered apex; surstylar setae long, reaching the sagittal plane; processi longi tubercular.    Diagnosis. Facial plate bare. Wing completely hyaline. Distance between crossveins r-m and dm-cu at least twice as long as r-m. Meron with unmodified setae. Legs yellowish brown, with femora distinctly darkened; hind tarsus with long, strong and dense setae ventrolaterally. Abdomen ground color dark brown or black. Male cercus short and broad, length/width ratio equal or less than 1.0; surstylus yellow, with an abruptly swollen lobe near base and a rounded apex; surstylar setae short, reaching at most halfway to the sagittal plane; processi longi tubercular. Female sternite 8 longitudinally ridged in the middle and with a scallop-shaped apex.
Material examined.   Table 1 Gastrus inermis Brauer, 1858: 464. Type locality: Austria, Neusiedlersee, Jois (as "auf der Rossweide bei Gyois am Neusiedlersee").  Meron bare. Legs yellowish brown, with femora distinctly darkened. Abdomen ground color yellow. Male cercus short and broad, length/width ratio equal or less than 1.0; surstylus yellow, with a rounded apex; processi longi tubercular. Female sternite 8 longitudinally ridged in the middle and with a scallop-shaped apex.  Remarks. Brauer (1858: 465) explicitly states that he examined "one pair" of adults that were hatched from puparia collected by the Austrian entomologist Alois Friedrich Rogenhofer in horse dung. 1♂, 1♀ in NHMW each carry two labels with the information "Oesterreich / Coll. Brauer" and "inermis / det Brauer". A fragment of a puparium carries labels with "Gastrus / inermis / det Brauer" and "Coll. Brauer". We consider the pair of adults to most probably represent original syntypes, but we are deliberately abstaining from designating a lectotype at this time.
Diagnosis. Male unknown. Antennal postpedicel long-oval. Facial plate setose. Wing completely hyaline. Crossvein dm-cu extremely weak, with only a faint trace; distance between crossveins r-m and dm-cu equal or less than length of r-m. Meron with unmodified setae. Legs black or black-brown. Abdomen ground color dark brown. Female sternite 8 longitudinally ridged in the middle and with a scallop-shaped apex.
Diagnosis. Facial plate bare. Wing with darkened patches with demarcated edges. Distance between crossveins r-m and dm-cu less than length of r-m. Meron with unmodified setae. Legs yellowish brown, with tibiae and tarsi more or less darkened. Hind trochanter of male with a long, spatulate process, of female with a tubercle; hind tibia and tarsus flattened distinctly in male, slightly in female; tarsomeres 2-4 shortened in both sexes, broader than long. Abdomen ground color yellow in both male and female. Male cercus elongated and broad, length/width ratio around 1.5; surstylus mainly black with yellow coloration basally, and a rounded apex. Female abdominal segment 7 distinctly longer than broad, sternite 8 longitudinally ridged in the middle and with a scallop-shaped apex. Hosts. Burchell's zebra (E. quagga burchellii). Distribution. Afrotropical -Burkina Faso, Democratic Republic of the Congo, Kenya, Republic of the Congo, Senegal, South Africa, Zambia.