Geron Meigen
Creators: name: Hall, Jack C.
name: Evenhuis, Neal L.
Publisher: name: Zenodo
Year: 2003
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Diptera
Bombyliidae
Geron

description: Genus Geron Meigen
Geron Meigen, 1820: 223. Rondani 1856: 165. Coquillett 1910: 546. Cresson 1919: 183. Bezzi 1924: 112. Painter 1932: 139. Hesse 1938: 873. Cole & Schlinger 1969: 234. Hull 1973: 203. Bowden 1974: 87. Evenhuis 1979: 13. Scarbrough & Davidson 1985: 1240. Evenhuis 1991: 42. Evenhuis 1994: 332. Evenhuis & Greathead 1999: 36. Type species: Geron gibbosus Meigen 1820 [= Bombylius gibbosus Olivier, 1789], by subsequent designation of Duponchel in d’Orbigny, 1845: 206.
The proper name to apply to the type species has led to nomenclatural confusion. Three different species have been listed as types of the genus, viz., Geron gibbosus Meigen (Rondani 1856; Painter & Painter 1965; Evenhuis 1989; Zaitzev 1989; Evenhuis 1994; Evenhuis & Greathead 1999), Bombylius gibbosus Oliver, 1789 (Painter 1932; Hull 1973; Bowden 1974; Evenhuis 1979), and Bombylius hybridus Meigen, 1804 (Bezzi 1924; Cole & Schlinger 1969). Meigen (1820) described Geron with two included species (G. gibbosus Meigen and G. halteralis Meigen) without designating a type species. Duponchel in d’Orbigny (1845: 206) designated Geron gibbosus Meigen as the type species. It is the first valid subsequent designation and was followed by Evenhuis (1989, 1991, 1994) and Evenhuis & Greathead (1999), but most workers subsequent to d’Orbigny missed this designation. The confusion over the correct type species by subsequent workers arises in the following way: Geron gibbosus of Meigen (1820) was an unjustified replacement of name for Bombylius hybridus Meigen, 1804. Earlier, Olivier (1789) described Bombylius gibbosus, which has been shown to belong to Geron (Painter 1932). Several authors therefore concluded that gibbosus Olivier is the oldest available name and should constitute the type species. With the inclusion of gibbosus Olivier in Geron, Geron gibbosus Meigen became a junior homonym. Meigen’s type of gibbosus [= hybridus Meigen] is located in the Museum National d’Histoire Naturelle, Paris, and has been examined by the junior author. Olivier’s type of gibbosus is apparently lost. The original descriptions of all of the above species are short, vague, and will fit any number of species. Greathead (1999) clarified the species limits of the taxa within the Geron gibbosus and Geron halteralis species complexes through genitalic studies of types and topotypic material. Through this study, it was concluded that many authors had misidentified Geron olivierii Macquart as Geron gibbosus (Olivier) (e.g., Hesse 1938, Zaitzev 1966).
Description. Head. Male eyes holoptic; female eyes dichoptic; front in male small, triangular, with shining white or silver­white scales, hair normally wanting; antenna black, scape cylindrical, one and one­half to three times the length of pedicel; pedicel about as wide as long; first flagellomere narrow, elongate, tapering from broadened base to acuminate apex; style minute, apical; proboscis narrow, elongate, extending beyond oral margin one and one­half to two times the head height; palpus short, one­segmented.
Thorax. Mesonotum convex giving a hump­backed appearance to the habitus in profile; scutellum without bristles. Legs thin, tibiae and tarsi with small setae; fore tibial bristles usually minute; females with or without specialized palynophilic setae on fore tarsi (Fig. 29) (Neff et al. 2003); legs with white hair and scales; pulvilli present, about as long as claws.
Abdomen. Tubular, tapering from base to narrowed apex; slightly broader in females, narrower in males; both sexes with eight visible segments.
Wing (Figs. 27–28). Hyaline to slightly infumate, with two submarginal and three posterior cells; anal cell closed at or slightly before wing margin; crossvein r­m at or beyond middle of cell dm; second submarginal cell short, about as long as apical width; crossvein m­cu sinuous (Fig. 28), occasionally straight (Fig. 27); anal lobe moderately developed.
Male genitalia (Figs. 30–57). Complicated in digitate or closed condition with gonocoxa in lateral view elongate, boat­shaped with a membranous “window” near apical third; gonostylus usually narrow, two to three times longer than high, with small hairs apically; four rami present; dorsolateral ramus (part of upper margin of gonocoxa), variously shaped but usually elongate with rounded apex; lateral ramus attached basally to dorsolateral ramus, shiny, thin, usually slightly curved, normally acuminate apically and coextensive with gonostylus; aedeagus [= distiphallus of Yeates (1994)] narrow, long, apically acuminate; passing through scale­like epiphallus of varying shapes; gonocoxa in ventral view either flat, with or without small projection, or with two broadly depressed areas separated by central ridge; genitalia in rosette or open condition with gonocoxa folded upward and inward; gonostylus bent upward and outward; lateral ramus bent up and out at nearly a right angle; dorsolateral ramus bent up and out; aedeagus moved posteriorly, projecting; anal lobes moved upward; aedeagal sheath separated and flattened, wing­like on either side of aedeagus; nearly every condition between the two extremes (digitate and rosette) is expressed.
Female genitalia (Figs. 1–26) without acanthophorites or sand chamber; vaginal furca consisting of two parts, upper part slightly curved, V­ or narrow U­shaped, membranous medially with an opening for common basal spermathecal duct; lower part variously shaped, usually more densely sclerotized; three spermathecae present, capsule not sclerotized, composed of coiled filaments or tubes; spermathecal duct long, thin, upper portion, above sperm pump with minute glands; sperm pump short, sclerotized collars (end plates) not evident; common basal spermathecal duct short.
Remarks on diagnostic characters. Cresson (1919) was the first to report on the variable flexible nature of the male genitalia in North American species; and Painter (1932) elaborated further on this phenomenon. The female genitalic structures have been studied and illustrated by a few authors (e.g., Scarbrough & Davidson 1985; Greathead 1999, 2001) and have proven to be more diagnostic in separating species of Geron for many regions of the globe than the male genitalia. The most comprehensive study of genitalia of Geron was that by Theodor (1983) on a few Palearctic, Afrotropical, and one Nearctic species. The Nearctic species belonging to Geron are probably among the most difficult of all the Bombyliidae to identify. The species are remarkably similar in appearance and the character states formerly used for separation, especially color, have proven to be almost totally unreliable. The body covering of hair and tomentum is loosely attached and, as a consequence, specimens are easily denuded. The sexes cannot be reliably associated unless taken in copulation, or secondarily, if collected together on flowers of the same species or together in swarms. We have relied heavily on label data in associating the sexes. Specific identification depends entirely on the configuration of the female vaginal furca and to some extent the male genitalia. The two forms of the male genitalia, digitate (closed) and rosette (open or expanded) presented difficulty in identification and comparing specimens. Nearly every position between the two types of genitalic configuration has been observed. Comparison of parts between the two types is difficult and often impossible without dissection because of the great amount of movement involved and the resulting cryptic condition of some of the parts. In reviewing the female vaginal furca care must be exercised when making comparisons, because of the curvature of the furca. The furca in all of the following descriptions and illustrations were viewed from the dorsal aspect. The furca also shows a good deal of variation in sclerotization and in the development of the basal lobes, this is most apparent in the more widespread species such as G. holosericeus Walker, G. senilis (Fabricius), and G. rufipes Macquart.
At present we are unable to specifically place most of the males in which the genitalia is in the rosette condition, unless reliably associated with identified females. There remain in the collections studied many probable new species. We have refrained from naming and describing them because of either the poor condition of the male genitalia or the paucity of specimens.
description: Published as part of Hall, Jack C. & Evenhuis, Neal L., 2003, Review of the subgenus Geron (Geron) Meigen in the Nearctic Region (Diptera: Bombyliidae: Toxophorinae), pp. 1-72 in Zootaxa 181 on pages 5-12, DOI: 10.5281/zenodo.156842