Microcercis infesta Foster 2024

Microcercis infesta (Becker) (Figs. 1, 2, 3, 5, 10, 12, 13, 18, 30) Oscinella infesta Becker, 1912: 108. Type locality: Woods Hole, Massachusetts. Deposited NMNH. NEW COMBINATION. Oscinella infesta.— Sabrosky 1936: 712–714, 721, 725 [in key, group D; discussion of type material; comparison with incerta and bispina; insularis as possible jr. syn.].— Sabrosky 1965: 780 [N. Am. catalog, distrib.]. Conioscinella infesta. — Davis and Gray 1966: 281, 284, 285–289, 292 [biology, salt marshes]. Incertella infesta. — Sabrosky 1980: 421 [n. comb.]; Foote, 2004: 168 [associated with Carex in freshwater marsh (this ID is in doubt)]. Diagnosis.—Ocellar triangle gray; vertex and occiput gray; postpedicel usually black dorsally, yellow ventrally but occasionally mostly brown with small spot of yellow on ventral margin; prosternum bright yellow; scutum gray, tomentose; postpronotal lobe and notopleuron gray tomentose; pleuron gray, dorsally tomentose, ventral half from propleuron to anterior katepisternum polished, posterior katepisternum and meron tomentose; foreleg mostly yellow, mid and hind femora gray, all tibiae yellow, hind tibia darker; tibial organ yellow; syntergite 1+2 usually bright yellow with small brown spots laterally and on mid line, remaining tergites brown with narrow yellow posterior margins; male cerci prominent, triangulate with rounded margin; surstylus short, polished black, triangulate with wide distal tip and smooth straight margin. Description.—Body length; female: 1.29−1.86 mm; male: 1.10−1.40 mm. Head: Ocellar triangle evenly grey tomentose; vertex and occiput grey; frons orangish yellow to bright yellow; scape and pedicel light brown to yellow, postpedicel black dorsally and around base of arista, remainder yellow; arista black, pubescent; face, palps, gena, and clypeus bright yellow in fresh specimens, sometimes turning orange over time; prementum polished bright yellow, labellum bright yellow; gena to eye ratio 0.20. Cephalic chaetotaxy: Fronto-orbital setae yellow to brown; interfrontal setae yellow to brown; ocellar setae yellow to brown; postocellar setae yellow to gray; outer vertical setae yellow to gray; inner vertical setae yellow to gray; postocular setae short, fine, dark; vibrissae yellow; subgenal setae yellow. Thorax: Prosternum bright yellow; prescutum polished black; scutum gray, tomentose; postpronotal lobe and notopleuron grey tomentose; pleuron gray, dorsally tomentose, ventral half from propleuron to anterior katepisternal margin polished black, most of katepisternum tomentose, small posterior portion of katepisternum and meron polished black; mediotergite polished black laterally, tomentose in center below the scutellum; scutellum concolorous with scutum; subscutellum tomentose; wing length 1.14–1.68 mm, hyaline, costal ratios 0.50:0.32:0.13; foreleg variable, typically entirely bright yellow except for a variably greyish area on posterior surface of fore femur; mid and hind coxae black; mid and hind femora light to dark grey tomentose except base and tips usually yellow, some specimens mid and hind femora entirely dark gray; all tibiae yellow except hind tibia may be greyish on dorsal surface; basal tarsomere yellow, apical four tarsomeres light brown; femoral organ as in figure 10; tibial organ usually somewhat indistinct, concolorous with rest of tibia. Thoracic chaetotaxy: Scapular setae absent; scutum and scutellum with yellow setulae. Abdomen: Syntergite 1+2 usually bright yellow with small brown spots laterally and on mid line, remaining tergites brown with narrow yellow posterior margins. Male terminalia (figs. 12, 30): epandrium grey tomentose with many setulae, male cerci prominent, triangulate with rounded margin; surstylus short, polished black, triangulate with wide distal tip and smooth straight margin. Female cerci brown, contrasting with bright yellow terminalia. Type material examined.—A male specimen from the original type series was deposited in the type collection of the NMNH and was assumed to be the holotype. Becker did not designate a holotype, rather a type series of one male and two females. Sabrosky (1936) stated that one of the females from the type series should be considered the type. This specimen was placed in an individual tray within the regular collection with a lectotype label and went unnoticed until now. Sabrosky did not specifically state that he designated a lectotype, saying only that “the other female must therefore be designated as the type of infesta, since Becker stated that the type series was in Melander’s collection”. As to the other female of the type series, Sabrosky noted that it has scapular setae and was therefore M. bispina. I found this specimen as well and it is indeed M. bispina. The LECTOTYPE, female, is missing the head, both wings, the right foreleg except the coxa, all of the scutellar setae except the right lateral and is mounted on a minuten pinned through the venter of the fly. The pin is inserted in a card that is mounted on an insect pin. The specimen has five labels: the top-most [faded yellow] has “Woods Hole Mass” type written; the second label [red] with “TYPE” typewritten; the third label [white] has “ Oscinella infesta Beck. ” handwritten in black ink with “det. Becker” typewritten under it; the fourth label has “A. L. Melander Collection” on a white label with a green dotted pattern on the right side; the fifth label [white] has “ LECTOTYPE ” typewritten on the first line, then hand written “ Oscinella infesta Becker ”, then type written“ designated C. W. Sabrosky” and hand written “1936”. Distribution.—Nearctic: Canada (New Brunswick, Nova Scotia, Prince Edward Island). United States (Alabama, California, Connecticut, Delaware, Florida, Georgia, Maine, Maryland, Massachusetts, Mississippi, New Hampshire, New Jersey, New York, North Carolina, Ohio [inland salt marsh], South Carolina, Texas, Virginia). Discussion.—This species is distinguished from other Microcercis species by the bright yellow syntergite 1 + 2 in most fresh material becoming darker in older specimens. In occasional specimens, however, the syntergite 1 + 2 is mostly gray. This variability can be problematic when separating M. infesta from M. insularis. The pattern of tomentum on the pleuron helps separate these two species in these cases. The male surstyli differ greatly between the two species, M. infesta being widely spatulate (fig. 30) and M. insularis showing a distinct projection on the medial surface of the surstylus (fig. 31). The pattern of the black polished areas of the pleuron are unique to M. infesta. Sabrosky (1936), incorrectly, in the key, characterizes M. infesta as having a completely tomentose pleuron while Becker (1912) in his original description states that the pleuron, with the exception of the anepisternum and anepimeron is glossy black. The polished pattern is more complex than Becker’s description states. See the description of M. infesta, above, and that of M. insularis, below, for details. Becker described the type as having the abdomen entirely brown with only the posterior margins yellow, however I found that the lectotype exhibits a yellow syntergite 1+2. The leg coloration described above is typical to most specimens though not universal. There are variations as some specimens can be darker than others. Notes.—I have collected this species in large numbers on both the wet and dry sand zone grasses on and near salt marshes. It typically shares the habitat with M. insularis, M. trifeminarum, and M. laytoni although M. infesta usually outnumbers those species. The number of individuals collected at a site often varies with the condition of the habitat. When the weather has been hot and dry for several days the numbers of individuals can decrease nearly to zero. I have collected all four species in both very hot, dry conditions and cooler, wetter days. For example, over the 17 th –24 th of July 2021 at the Sally Cove site described above, I found hundreds of individuals at the start of the period with a gradual decrease to almost none as the week continued with no rainfall. All the specimens I examined were from coastal and inland salt marsh localities from New England through Florida and the Gulf States to California.

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