Rhizocecis Gagné, 2013

Gagné, Raymond J., 2013, Four new genera of Nearctic Cecidomyiidae (Diptera) for species previously incorrectly placed, Zootaxa 3701 (2), pp. 148-158 : 155-156

Rhizocecis Gagné , new genus

Figs. 16–20

Diagnosis. This genus can be separated from all other genera of Lasiopteridi by the following combination of characters: C broken immediately posterior to junction with R5; R5 reaching C slightly anterior to wing apex; empodia as long as tarsal claws; tarsal claws with basal tooth; second through seventh abdominal tergites of both sexes with single, continuous posterior row of setae and without lateral setae; sternites lacking anterior pair of trichoid sensilla; gonocoxal mediobasal lobes prominently divided into dorsal and ventral lobes, the ventral lobe tapered; gonostylus widest at base, tapering gradually to narrow apex; female eighth abdominal tergite as long as seventh, undivided; ovipositor short, not protrusible, bare dorsally, with scattered setae ventrally and without apparent dorsolateral sclerite; cerci discrete, ovoid, with, besides other scattered setae, several thick and blunt-tipped setae apically. The third instar larva has a spatula and only 4 lateral papillae present on each side of midline.

Description. Adult. Head: Eye facets circular, contiguous on ventral half of eye, farther apart dorsally, eye bridge 4 facets long. Antenna: scape and pedicel with several setae ventrally; 11–14 flagellomeres; all but last flagellomere with long necks in male, about one-third length of node, without necks in female. Frons with many setae and scales. Labella large, hemispherical in frontal view, with several stout setae. Palpus 4–segmented, third and fourth segments thinner and each much longer than second.

Thorax: Scutum with 4 longitudinal rows of setae mixed with some scales, the 2 dorsocentral rows several setae wide anteriorly, narrowing to one seta wide before vanishing shortly before scutellum, the 2 lateral rows 2–3 setae wide mixed with some scales and continuous along length of sclerite. Scutellum with many setae and scales laterally. Anepisternum with a few scales dorsally; anepimeron setose; pleura otherwise bare. Wing: C broken beyond junction with R5; R5 reaching C slightly anterior to wing apex; M not apparent; CuA forked. Acropod (Fig. 16): claws with basal tooth; empodia as long as claws; pulvilli about 1/3 as long as claws.

Male abdomen: First through sixth tergites rectangular, with anterior pair of trichoid sensilla, single, continuous posterior row of setae, and without lateral setae, remainder of tergite surface thickly covered with scales; seventh tergite unsclerotized posteriorly, without posterior setae, with anterior pair of trichoid sensilla and elsewhere covered with scales; eighth tergite half as long as seventh, the anterior pair of trichoid sensilla the only vestiture. Second through eighth sternites rectangular, with mostly double horizontal row of posterior setae, the rows of setae mixed with scales, another setal row across sclerite at midlength, lacking anterior pair of trichoid sensilla, elsewhere completely covered with scales. Terminalia (Figs. 17–18): cercus ellipsoid, with several apical and subapical setae, especially ventrally; hypoproct parallel-sided, deeply concave, resulting lobes each with 2 apical setae, otherwise evenly setulose on both surfaces; gonocoxite cylindrical laterally, its mediobasal lobe subdivided into a short dorsal lobe and a longer, tapered ventral lobe closely abutting but shorter than aedeagus, both lobes long-setulose, the ventral lobe glabrous ventroapically with 2 setae on raised bases; gonostylus widest at base, tapering to apical tooth, mostly glabrous and ridged dorsally, setulose basally and on most of venter except apically.

Female abdomen (Figs. 19–20): First through seventh tergites as for first through sixth in male; eighth tergite of same length as seventh but 1/3 as broad, a few short setae posteriorly, a pair of anterior trichoid sensilla, otherwise naked. Second to seventh sternites as for male, particularly in lack of anterior pair of trichoid sensilla; eighth sternite more weakly sclerotized than seventh but well-defined by presence of many setae and setiform scales. Ovipositor short, not protrusible, bare dorsally, with many setae apicoventrally; cerci discrete, ovoid, with many setae, those near apex thicker than remainder; hypoproct broad, with two apical setae.

Larva. Third instar: Short, cylindrical. Integument verrucose. Head short, hemispherical, cephalic apodemes shorter than head capsule, antennae less than twice as long as wide. Spatula clove-shaped. Papillae with very short setae; lateral papillae in a single group of four on each side of midline; 8 terminal papillae.

Type species, Cecidomyia rhois Coquillett (1895) .

Material examined (all from tuberlike galls on aerial rootlets of Toxicodendron radicans (L.) Kuntze ( Anacardiaceae ). Syntypes of Cecidomyia rhois , ♂ and ♀, Lebanon Springs, New York, USA, III-1894, W.H. Harrison; larva, Vienna, Virginia, USA, XI-28-1937, J.C. Bridwell; and the following, all from Silver Spring, Maryland, USA, and collected by R.J. Gagné: 3 larvae, II-2-1983; larva, IV-9-1991; 2 ♀, III-25-1994; female, larva, III-7-1995; ♂, 2 ♀, IV-2006. All specimens are in the National Museum of Natural History, Smithsonian Institution, Washington, DC.

Etymology. The name Rhizocecis is a combination of the Greek words for root and gall, with reference to the aerial rootlet galls made by the only included species. The gender is feminine.

Remarks. The single species placed here is responsible for tuberlike galls on aerial rootlets of Toxicodendron radicans (L.) Kuntze ( Anacardiaceae ). It had previously been placed in Dasineura (Gagné 2010) . Apomorphic characters are the loss in both sexes of the anterior pair of trichoid sensilla on all abdominal sternites, the lack of lateral setae on the tergites and the reduction of larval lateral papillae from six to four on each side of the midline. One should expect that a non-protrusible ovipositor with discrete cerci, as found here, has to be plesiomorphic. To derive such a species from one with a long-protrusible ovipositor with fused cerci, the condition of almost all genera of Lasiopteridi, would presumably require all the musculature, makeup of the postabdominal terga and sterna, and the internal organs to return to the pristine condition. Not very many Lasiopteridi have discrete cerci and non-protrusible ovipositors. Interestingly, most of them are Neotropical, but none serves as a likely home for C. rhois . Possibilities examined were Elachipalpus Maia & Nava (2011) , Eugeniamyia Maia, Menconça & Romanowski (1997) , Jorgenseniella Maia (2005) and Mayteniella Maia (2001) . Males of these genera preclude placing C. rhois with them: Elachipalpus has a very broad, undivided hypoproct and the gonocoxal apodeme is divided; Eugeniamyia has extremely long and thin mediobasal gonocoxite lobes that are as long as the aedeagus; Mayteniella has a bulbous gonostylus with a subapical tooth; and Jorgenseniella has short gonocoxal lobes that are clearly separated from the short aedeagus. Further, all differ from Rhizocecis because they have lateral setae on the adult abdominal tergites and a full complement of six larval lateral papillae on each side of the thoracic midline.