Synonyms and other taxonomic changes
This species group needs revision; its members are usually impossible to tell apart from photographs. Traditional taxa included here are
L. index McAtee and
L. ithypyga McAtee.
Bullington (1986; unpublished dissertation) grouped L. index with some of the small blackish species (e.g. L. canis, L. winnemana), which were split into a new genus. He placed L. ithypyga and L. sicula in the genus Choerades based on genitalic differences.
Explanation of Names
Laphria index McAtee 1919, Laphria ithypyga McAtee 1919
Identification
Dark, trim, medium-sized or small robber flies with a distinctive golden triangle of hairs on the thorax and golden-orange on the dorsal surface of the abdomen. Distinctive as a group, but unlikely to be identified to species from photographs. (Males can be distinguished based on abdominal anatomy, but females are hardly distinguishable even from specimens.)
Males of the two species can be distinguished as follows:
Genital bulb: quite large in L. index, substantially smaller in L. ithypyga
Projection[s] at the posterior margin of tergite 6: paired and conspicuous in
L. index, tiny and unpaired in
L. ithypyga (see
Norm Lavers' photo).
Live photos rarely show these differences.
Original descriptions
(1):
L. index: Mystax black; pollen and decumbent pile of face silvery; occiput, coxae pleurae, fascia on front of thorax, gray to white pollinose, hair where present concolorous. Thorax with a median triangle of pale to reddish golden hair about as wide of scutellum behind rapidly narrowing and evanescent anteriorly; remaining pile on disk of thorax consisting of longer whitish, sometimes golden and shorter black hairs, bristles black. Hair on scutellum tends to be paler and the marginal bristles are white. Pile of abdomen, except for whitish hairs on sides of first three segments, pale to reddish golden; rather dense in well preserved specimens, but apparently rather easily lost. Hair of legs gray and black. Wings fumose paler toward base. Hypopygium black, black bristled; apical process somewhat reddish, beveled on outer side, but not twisted, dccurved forming with apex of forceps a figure like an opposed thumb and index finger. (Fig.17) Length 13−18 mm. So far I have not found a way of certainly distinguishing the females of this species from the next (ithypyga) They appear to be the more robust specimens with the golden thoracic triangle more conspicuous.
L. ithypyga: Scarcely differs from last in general appearance but male genitalia are very distinct. Hypopygium black, black bristled, straighter than usual in the genus; apical process not twisted, broad, stout forming the principal part of apex of forceps; hollowed out within and forming with lower apical angle of forceps a considerable emargination which is broadest distally. (Fig.18). Length 12−17 mm.
Figures referenced above:
