Allotrichoma Becker

Mathis, Wayne N. & Zatwarnicki, Tadeusz, 2012, Revision of New World Species of the Shore-fly Subgenus Allotrichoma Becker of the Genus Allotrichoma with Description of the Subgenus Neotrichoma (Diptera, Ephydridae, Hecamedini), ZooKeys 161, pp. 1-101 : 18-21

Subgenus Allotrichoma Becker

Allotrichoma Becker 1896: 121 [type species: Hecamede lateralis Loew, by original designation]. Hendel 1936: 104 [discussion]. Wirth 1965: 736 [Nearctic catalog]. Runyan and Deonier 1979: 123-137 [discussion, natural history, phylogenetic analysis]. Mathis 1986a: 129-130 [diagnosis and discussion]; 1991: 6-7 [diagnosis]. Mathis and Zatwarnicki 1995: 149-154 [world catalog]. Also see generic synonymy.

Epiphasis Becker 1907: 301 [type species: Epiphasis clypeata Becker 1907, monotypy]. Cogan 1984: 131 [synonymy].

Diagnosis.

Small to moderately small shore flies, body length 1.15-2.40 mm.

Head: Frons mostly unicolorous, at most with narrow, anterior fronto-orbits slightly lighter in color, lacking distinctively colored ocellar triangle; pseudopostocellar setae subequal in length to intrafrontal setae. Pedicel with well-developed, proclinate, dorsal seta. Facial coloration sexually dimorphic, males unicolorus and darker; face with dorsal 2/3 between antennal grooves shallowly carinate, becoming more prominent ventrad of antennal grooves, slightly tuberculate; clypeus usually mostly microtomentose, dull colored; palpus blackish.

Thorax: Mesonotum generally dark brown; chaetotaxy generally well developed; prescutellar acrostichal setae much larger than other acrostichal setae and more widely set apart; presutural seta well developed, length subequal to notopleural setae; katepisternum with 2 setae, 2nd seta smaller and inserted below larger seta. Wing mostly milky white; veins behind costa brownish; alular marginal setulae short, less than 1/2 alular height. Legs: tibiae dark, concolorous with femora; male hindtibia bearing 3-4 semierect, preapical setae on dorsum.

Abdomen: Fifth tergite tubular, elongate, well sclerotized, length subequal to that of 4th, bearing a posteroventral process in conjunction with 5th sternite; 5th sternite highly modified, produced as a ventral flap or processes. Male terminalia: cerci well sclerotized, elongate, often twice length of epandrium (probably used at least partially as a clasping structure); surstylus fused to ventral margin of epandrium, usually appearing as an elongate extension of the epandrium (secondarily lost in some species), bearing apical setulae; a single gonite (presumably fused pre- and postgonites) sheathing aedeagus; aedeagus simple, tubelike, sometimes slightly arched; hypandrium generally reduced, fused basally to base of gonite, in lateral view appearing strap or bar-like.

Distribution.

Except for polar regions and South America, the subgenus Allotrichoma occurs worldwide, although with greater diversity in temperate zones ( Mathis and Zatwarnicki 1995).

Natural history.

Very little is known about the natural history of any species of Allotrichoma , especially larval habitats and immature stages. The brief and few references are as follows:

From the island of Guam, Bohart and Gressitt (1951: 85) wrote that "Adults [of apparently Allotrichoma livens Cresson] swarm around foul-smelling mud and puddles and are especially abundant in the mud of pig pens around feeding troughs where contamination by garbage and pig feces is heavy. The larvae breed in pig droppings and pupate at the surface of the droppings. Although maggots were not observed in the contaminated mud of pig pens, it is probable that most of them develop there."

"This fly is extremely common wherever found. It is apparently not present around mud which is free from contamination. It probably has no medical significance, and control is unnecessary."

Bohart and Gressitt (1951: plate 11) also presented an illustration of the puparium of Allotrichoma livens .

Runyan and Deonier (1979: 123-137) summarized information on the natural history of Allotrichoma and published the only illustrations on the eggs, puparia, and cephalopharyngeal skeleton of Allotrichoma (Allotrichoma) simplex and Allotrichoma (Pseudohecamede) abdominale and the egg of Allotrichoma (Neotrichoma) atrilabre (as Allotrichoma yosemite ). They also reported that specimens of these three groups occur in habitats that are rich in decaying organic matter, including limnic wrack, stag nant pools, and vertebrate excrement (muskrat, raccoon, horse, pig, and cow feces). Sand shores and piles of lawn clippings were also added as habitats for adults, which have also been swept from the inflorescences of a wide variety of plant species. Runyan, the senior author of this paper, also collected adults on dead fish and crayfish carcasses.

We too have collected adults from the kinds of habitats reported above but emphasize that much of our success in collecting was on fairly undisturbed, sandy shores associated with both lotic and lentic aquatic systems, sometimes with the adjoining shore having alkali and perhaps other salts. Moreover, we often found several species occurring microsympatrically together. We commonly found two species together and at a few sites in the West, we collected up to five species occurring together. Based on this finding, we have been especially hesitant to designate females as paratypes, not knowing how to distinguish between them, from localities where multiple species occur. Our discovery begs the question about how these various species are partitioning the habitat where and when they occur together microsympatrically.

Discussion.

The monophyly of this subgenus is corroborated by several characters that Runyan and Deonier (1979) and more recently that Krivosheina and Zatwarnicki (1997) have identified. These synapomorphies are as follows: (1) Surstylus (=gonostylus; fused to epandrium, therefore called surstylus) as a simple appendix, terminating with apical setulae, or secondarily reduced; (2) gonites incised apically; (3) cerci generally elongate, in some tropical species fused to each other, rarely oval; (4) 5th sternite with a ventrally produced, paired, lateral flap (one flap on each side) and a medial process; (5) 4th tergite of male largely vestigial, forming two small bands close to the anterior margin of 5th tergite.

An objective of this revision was to report the determination of species that may have a Holarctic distribution, as noted in the introduction. For example, among the seven species reported from the Nearctic Region, Wirth (1965) listed two, Allotrichoma laterale (Loew) and Allotrichoma trispinum Becker, with Holarctic distributions. Wirth also cautioned ( 1965: 736), however, that "The species are poorly understood and distributions records need revision after a study of male genitalia." Our research, which has emphasized characters from structures of the male terminalia, indeed reports not two but three Holarctic species, but none is one of the species names that Wirth reported earlier. The Holarctic species reported in this revision are: Allotrichoma bezzii , Allotrichoma schumanni , and Allotrichoma simplex . The first two are species first named from specimens collected in Europe and then discovered here, and the last species, Allotrichoma simplex , has as its type locality, “Maryland,” and has now been found to be the senior synonym of taxa occurring in Europe. We call attention to these discoveries to emphasize that studies of limited geographic scope, such as this revision of New World species, need to consider congeners on a global basis to avoid misidentifications and incorrect distributional data.

We can presently identify only males of this subgenus, and as a consequence, we have only used structures of the male terminalia in the key to the New-World species of this subgenus that follows.

Key to Males of New-World Species of Allotrichoma (Allotrichoma)