Grotella stretchi Barnes and Benjamin 1922
Diagnosis: Grotella stretchi is a non-descript
species primarily from the Mohave Desert region of southern California
and southern Nevada. The species flies primarily in April and May. The
forewing is either a light cream-white or white. The hindwing is suffused
with dull gray-brown. Ocassionally there are one to three minute black
dots on the forewing. Wing length: mean = 10.38 mm, standard deviation
= 0.49 mm, n = 10.
Distribution: This range of this species appears to be almost restricted to the Mohave Desert region of southern California and southern Nevada. It has been taken in San Diego, Riverside, Los Angeles, San Bernardino, and southern Inyo counties in California and Clark County in southern Nevada. However there is a single specimen from Alamosa County in southwestern Colorado in the USNM. At this Colorado locality it is sympatric with parvipuncta. The species is moderately variable. Superficially the color of the forewing varies from almost pure white to strongly shaded with cream-white. Populations tend, but are not always, of one color type, some populations tending to be cream-colored and others mostly white. However I have not found any geographical trend in forewing color. The sized and shape of the clasper of the valve of the male genitalia is also variable. The two names stretchi and vagans were based on individuals with different sized and shaped claspers. However additional dissections revealed that clasper size is very variable and all possible integrades occur.
Identification Quality: Excellent
This species is mostly likely to be confused with parvipuncta. The two species are largely allopatric in range. Grotella stretchi appears to be limited to the Mohave Desert region but parvipuncta is more a species of New Mexico, Arizona, and western Texas. However there is a single specimen of parvipuncta in the USNM from San Bernardino County and so geographical range cannot always be used. The best superficial character to use to separate the two species is found on the outer side of the prothoracic tibia. In stretchi there are one, or ocassionally two, spines on the outer edge of the prothoracic tibia in addition to the usual apical spine. In parvipuncta there are no additional spines on the outer edge. Ventrally in most specimens of stretchi the majority of the wing is strongly suffused with dark gray. However the apex of the wing and costal fourth are white and this white region usually (but not always) strongly contrasts with the remainder of the wing. In parvipuncta, however, there is never this contrast between the apical and central portions of the wing. The central prominence of the frontal process tends to be more laterally compressed in stretchi than in parvipuncta. However the shape the central prominence is variable and this average difference does not always hold for individual specimens. The two species are readily separable by characters of both the male and female genitalia. In the male genitalia stretchi has a strong clasper. The clasper is absent in parvipuncta. In the vesica of the aedoeagus the basal spines are larger and are sited on rounded bases in stretchi but in parvipuncta the spines are smaller, more numerous and not on rounded bases. The female genitalia are markedly different from those found in the species superficially most like it, i.e. parvipuncta, dis, and blanca. In particular the ovipositor are simple square plates and are not modified. In contrast in parvipuncta, dis, and blanca the ovipositor lobes are elongate and pointed apically. The ostium is cup-shaped. The ductus bursae is membranous and relatively short, approximately one and one-half times as long as wide. The ductus bursae joins a quadrate, internally ridged portion of the corpus bursae. This quadrate portion of the corpus bursae joins a large appendix bursae which curves to the right when viewed ventrally. The rest of the bursa is approximately four times longer than wide. In contrast the corpus bursae of dis, parvipuncta, and blanca is much longer and narrower and the appendix bursae exists as a c-shaped projection at the junction of the long, thin ductus bursae and the long, thin corpus bursae.
Grotella stretchi might be confused with dis and blanca. However the forewings of dis and blanca and always pure white, but in stretchi the forewing usually (but not always) has a cream-white tinge to it. In addition the white scales of the front of the head continue laterally between the eye and the rim of the frontal process in stretchi and parvipuncta but in dis and blanca these scales are black or dark brown-gray. In addition the geographical range of stretchi does not appear to overlap the provenance of either blanca or dis. Grotella stretchi might be confused with the sympatric species Grotellaforma lactea. However lactea lacks spines on either the prothoracic or mesothoracic tibiae, but in stretchi spines occur on both parts of the legs. In addition lactea is a smaller animal than stretchi