Tachytrechus sanus Osten Sacken, 1877

Runyon, Justin B., 2022, Nematode-induced demasculinization of Nearctic Dolichopodidae (Diptera) with five new synonyms, Zootaxa 5092 (5), pp. 545-558 : 552

Tachytrechus sanus Osten Sacken, 1877

( Figs 27–39 )

Tachytrechus sanus Osten Sacken, 1877: 316 .

Tetrechus spinitarsus Van Duzee, 1924: 43 .

Tachytrechus boharti Harmston, 1968: 15 , syn. nov.

Tachytrechus duplicatus Harmston, 1972: 157 , syn. nov.

Tachytrechus mchughi Harmston, 1972: 156 , syn. nov.

Nematode. Parasitylenchus myiophagus Poinar & Runyon (Parasitylenchidae) .

Demasculinized males examined. Holotype ♂ of Tachytrechus boharti , USA, California, Sierra County, Yuba Pass, 7 July 1964, RM Bohart ( UCDC) [photos]; holotype ♂ of Tachytrechus duplicatus , USA, Oregon, Baker [City], 25 July 1965, FC Harmston ( CAS) [photos]; holotype ♂ of Tachytrechus mchughi , USA, Oregon, Latourele [Latourell] Falls , 2 August 1962, RA McHugh ( CAS) [photos]; 1 ♂, USA, California, Trinity County , Scott Mountains , Stoddard Mine , 7200 ft, 25 July 1981, DM Gordon ( MTEC); 2 ♂, USA, Montana, Ravalli County , 0.8 km NW Skalkaho Pass, roadside seep, 18 August 2002, 7270 ft, R Hurley & J Runyon ( MTEC); 4 ♂, USA, Montana, Gallatin County , Bridger Mountains , Johnson Canyon , large hillside spring, 30 July 2010, N45°57.73′ W111°01.61′, JB Runyon ( MTEC).

Remarks. Demasculinized males of T. sanus are characterized by having: (1) a wider face that is light yellow to wholly silver (cf. Figs 27, 28 ), (2) arista shorter with reduced lamella, but arista length and size of lamella is variable ( Figs 33–39 ), (3) legs darker: fore coxa mostly dark, all femora with approximately basal half dark brown, mid and hind tibiae brown on apical third or more (cf. Figs 30, 31 ), (4) the posterior row of setae on front tibia reduced in size (noticeably thickened and flattened in normal males) and usually in number (4–8 in infected versus 8–10 in normal males), (5) front tarsus lacking silvery pile, and (6) hypopygium unusually small and incompletely rotated (cf. Figs 30, 31 ). The darker legs are an interesting example of infected males converging with the female form. Females of T. sanus have wholly dark front coxae and mostly dark femora and tibiae, but these are mostly yellow in normal males. The characters above vary considerably across the infected specimens (especially the arista, extent of brown on legs, size and number of setae on front tibia, and size of the genitalia), perhaps related to the extent of nematode infection.

Harmston described T. boharti from one male collected at Yuba Pass, California noting that it is distinguished by the spear-shaped arista ( Fig. 37 ). Tachytrechus duplicatus was described from one male collected at Baker, Oregon and T. mchughi from two males collected at Latourell Falls, Oregon. A close resemblance of both species to T. boharti was noted. Although the presence of nematode(s) within the holotypes of T. boharti , T. duplicatus , and T. mchughi have not been confirmed, synonymy with T. sanus is proposed based on: (1) demasculinized specimens of T. sanus match the descriptions of T. boharti , T. duplicatus , and T. mchughi ( Harmston 1968, 1972), and (2) the holotypes each show signs of nematode-caused demasculinization that fall within the spectrum of variation caused by nematode-induced demasculinization of T. sanus (see above). Normal males of T. sanus were collected with demasculinized specimens at most sites, including four normal specimens with the T. boharti holotype (UCDC).

Figures

FIGURES 27–39. Effects of parasitism by parasitylenchid nematodes on males of Tachytrechus sanus Osten Sacken. 27. Head of normal male. 28. Head of infected male. 29. Head of female. 30. Habitus, normal male. 31. Habitus, infected male (holotype of T. boharti Harmston). Note shorter arista (left arrow), darker front coxae and femora (middle arrow), and smaller genitalia (right arrow). 32. Male with abdomen opened to reveal nematodes of Parasitylenchus myiophagus Poinar & Runyon. Note numerous nematodes in abdominal cavity. Arrows indicate two nematodes removed from abdomen. 33. Male antenna, normally developed. 34–39. Antennae of infected males, showing variation caused by nematodes. 34, 35. Antennae of two infected males collected together in Ravalli County, Montana, USA. 36. Antenna of infected male from Gallatin County, Montana, USA. 37. Apex of arista, holotype of T. boharti. 38. Apex of arista, holotype of T. duplicatus Harmston. 39. Apex of arista, holotype of T. mchughi Harmston.