Hybomitra trispila (Wiedemann)

Goodwin, James. T., 2013, Immature stages of some eastern Nearctic Tabanidae (Diptera). IX. Chrysops beameri Brennan and Hybomitra trispila (Wiedemann), Insecta Mundi 2013 (318), pp. 1-5 : 3-4

Hybomitra trispila (Wiedemann)

Mature larva ( Fig. 3 ). Body pale brown or beige; 24-28 mm long; stocky. Head capsule length 3.0- 3.8 mm, greatest width 0.8-0.9 mm. Anal segment swollen. Respiratory siphon relatively small and somewhat conical; length 0.5-0.7 mm, about equal to its basal diameter. Tracheal trunks slender and gradually tapered anteriorly; diameter of each in preanal segment about 0.4 mm. Striations prominent; present on usual aspects of all segments; spaced approximately 0.08 mm dorsally and ventrally and 0.06 mm laterally on prothorax, progressively narrower on successive thoracic segments to 0.05 mm dorsally and ventrally and 0.04 mm laterally on first seven abdominal segments, widening to 0.06 mm on all median aspects of anal segment. Anterior pubescence encircling prothorax, narrowly absent mid-dorsally and ventrally from meso- and meta-thorax, forming progressively smaller bands or patches on dorsal or dorsolateral surfaces of first three or four abdominal segments and ventral surfaces of first five abdominal segments; thoracic pubescence dark, especially on meso- and meta-thorax above dorsolateral furrows. Posterior pubescence, if present, restricted to faint area at end of anal segment.

Pupa ( Fig. 4 A-4B). Body 18-23 mm long; uniformly pale yellowish-brown to brown. Antennal ridges small to moderate in size with rounded crests; elevated about 0.1 mm. Frontal ridges absent. Callus tubercles very small to absent. Vertical and orbital tubercles minute or absent. Antennal sheaths relatively smooth or annulated; about 0.5 mm long and broad; reaching epicranial suture only in females. Thoracic spiracles 0.5-0.6 mm long and broad; evenly bowed or with posterior arm somewhat straightened; not exceeding anterior dorsal margin of thorax. Abdominal fringes traversing usual sclerites; essentially uniseriate on anterior sternites; biseriate elsewhere. Spines of anterior series very small on sternites, pleurites, and lateral portions of tergites; very stout and comprising bulk of spination medially on tergites, the larger spines here at least 0.13 mm broad. Posterior spines long and slender; restricted on each tergite to a submedian pair and several lateral pairs. Tergum 7 with 24-36 spines, the longer about 0.6 mm. Dorsal and sometimes lateral preanal combs reduced. Dorsal, lateral, and ventral tubercles of aster approximately 0.3, 0.7, and 0.25 mm long, respectively; dorsal and lateral pair strongly inclined dorsally, often at nearly the same angle.

Collections. All larvae of H. trispila were found at Holly Lake Ranch, Wood County, Texas near the west shore of the Clear Creek branch of Greenbrier Lake (32.728667, -95.185667). The collecting site is a hillside seepage area about 20 m long and 10 m. wide with a small stream about 0.5 m wide flowing through the seepage area. At the time of collection, the seepage area was a combination of wet, silty sand mixed with considerable decomposing organic material and was relatively flat even though the stream sloped gradually toward Greenbrier Lake about 40 m. downstream. Although the seepage area is usually wet year round, but the extent of the wet surface area varies depending on amount of recent rainfall. Other species of Tabanidae found in association included Chrysops brimleyi Hine , C. geminatus Wiedemann , C. pikei Whitney , Tabanus atratus Fabricius , T. petiolatus , and T. trimaculatus .

Comments. In the key to larvae of Hybomitra Enderlein presented in Teskey (1969) larvae of H. trispila would key to the second half of the final couplet, couplet 17, which identifies pupae of H. trispila subspecies sodalis (Williston) . Hybomitra sodalis is now afforded specific rank. If an additional couplet was written, it could only note that the only difference between the larvae of these two species is that the anterior pubescence narrowly encircles the first abdominal segment in H. trispila whereas it is absent laterally in H. sodalis .

In Teskey’s key to pupae of Hybomitra , pupae of H. trispila would also key to those of H. sodalis (Teskey’s couplet 12), and no characters have been found that will separate the pupae of these two species.

The specimens on which the above descriptions are based are deposited in the Florida State Collection of Arthropods, Gainesville, FL.

Figures

Figures 3-4. Hybomitra trispila. 3) Illustration of the pubescence pattern of in lateral view. 4) Images of the pupa: A. ventral view of frontal plate; B. dorsal view of posterior segments of abdomen.