Not for citation or distribution without prior permission ofauthor.

An interesting new larval form of Argia. [inprep.]

by Ethan Bright

Insect Division, Museum of Zoology, University of Michigan, AnnArbor, MI 48109-1079

 

Introduction

 

Dr. Carl L. Hubbs and other well-known researchers in theUniversity of Michigan Fish Division were quite active in researchingthe fish fauna of the southwestern United States and most of Mexicofor over 50 years. These researchers often saved many of the aquaticinsects caught in their fishing seines, thus contributing thousandsof specimens - including many odonate larvae - now deposited in theUMMZ-Insect Division. We have just begun to sort through and identifythis large but somewhat unorganized treasure. One such specimen is aunique and fascinating larval specimen of Argia that had been inunsorted storage for over 60 years (Figure 1). I have been unable toassociate this specimen with recent larval keys (Westfall and May1996) and descriptions (Westfall 1990, Novelo-Gutierrez 1992)appropriate for collection area.

The specimen, collected by the family of Dr. Hubbs and EarlMangum, on 22 August 1938, originated from a tributary of MurrayCreek, in White Pine Co., Nevada. An entry from Dr. Hubb's fieldnoted that the specimen was collected from "springs on GeorgetownRanch, in meadows immediately north of [the] railroad yards of EastEly. The water was clear and cool, the creek generally choked withcress and Potamogeton." The stream was characterized as a series ofminute pools and riffles, with depth up to 2 feet in some headsprings. Murray Creek was characterized as "the open sewer of Ely,and is said to irrigate Georgetown Ranch which is owned by The WaterCo. The largest spring, on the south side of the railroad tracks wasthe largest and is reported to have contained many of the minnowsbefore it was drained out, cemented in and used in the water supplyof Ely (most of which comes from above town)." The specimen wasoriginally preserved in 10% formalin, then transfered to 70% ethanol.

 

Description

Color (in preservative) tan-yellow, body stout and short. Length(excluding gills) 9.05 mm; abdomen (without gills) 4.8 mm; hind femur3.0 mm; hindwing pad 2.5 mm; gills missing.

Head (see Figure 2): fairly uniform in color, except for a darkbrown transverse marking between the eye that almost touchesmedially, posteriorly to this a lighter band, and posterior to that aslightly darker brownish band to the posterior margin of the head.Occipital lobe with prominent posterolateral tubercles, thicklycovered on dorsal and ventral surface with approximately 20 thicksetae on each tubercle. Eye ventrally surrounded by a line of smallerthick setae. Dorsal surface of head covered with thin hairs. Widthacross eyes 7.0 mm, width behind eyes narrower ( 6.0 mm), and thenconsiderably wider across cephalic tubercles (7.1 mm). Antennaeuniform in color, total length 1.65 mm, slightly shorter thanmiddorsal length of head, ratio of lengths of antennomeres: 0.55,0.73, 1.00, 0.52, 0.39, 0.30, 0.18, seventh antennomere not stronglydifferentiated from the sixth. Length of head from frontal shelf toback of head 3.4 mm. Labium tan- to yellow-brown,prementum-postmentum articulation extending posteriorly slightly pastthe base of anterior margin of mesocoxae. Prementum broad, sidesdivergent apically, middorsal length in dorsal view of extended hinge2.2 mm, width across palpal lobes 2.0 mm, and basal width 1.15 mm(0.58x its apical width). Ligula moderately convex (Figure 3),strongly denticulate with small setae at near apical margin of eachminute denticle, lateral margin with 14 stout setae along the apical2/5, no premental raptoral or basal setae. Palpal lobes with 4 palpalsetae, posterior 4th small, movable hook about 0.68 mm, two pointedhooks slightly incurved and slightly darker than base color at theirtips, lateral one shorter (0.61mm) and slightly a bit less than 3xthe length of the mesal one (0.21 mm).

Thorax: yellow brown, anterodorsum of pronotum with spiniformsetae, inferior margin of proepisternum evenly rounded with thicklyspinulose setae interspersed with long thin hairs; this margin, inlateral view, slanted at a posterior-to-anterior angle ofapproximately 80 degrees. Synthorax somewhat robust, evenly colored,with wing sheaths somewhat translucent, extending roughly to middleof abdominal segment 4. Legs yellow, apparently unbanded, althoughthe apical portion of tibia slightly testaceous. Meso- and metafemurflattened (Figure 4), somewhat arcuate, anterior margin with single,regular row of small spinulose setae interspersed with thin hairs,posterior side with double row of longer spinulose setae interspersedwith longer, thin hairs. Meso- and metatibiae arcuate, with spiniformsetae on apical, ventral side. Tarsi straight to slightly arcuate,ventrally with double row of spiniform setae, dorsal side withscattered, thin hairs. Right mesotarsal claw apparently malformed.

Abdomen: segments generally uniform in color, except for amiddorsal light longitudinal line, very thin in basal segments andconsiderably thicker at Ab8-10, almost like a middorsal lighttriangle. Posterior margin of each segment with 1 even row of thicksetae, elsewhere segments with scattered setae interspersed with thinhairs, and with very long hairs centered mesally on tergites. Femalegonapophyses extending to posterior margin of 10, in ventral viewtips somewhat sharp and slightly divergent. Gills missing.

 

Comments

 

The well-developed wing pads indicate a fairly mature specimen,and the combination of the following characters would indicate morelikely a new and unusual larval form of an undescribed species,rather than an aberrant form of a known species:

1. Cephalic lobes with hypertrophied tubercles (Figure 2)

2. Lack of obscure leg rings

3. Transverse band on the head between compound eyes (Figure 2)

The first characteristic is especially amazing because it has notbeen previoulsy recorded in any other member of the genus. Thisspecimen reflects similarities to the Argia extranea-vivida group,with the antenna slightly shorter than the head and slightlyflattened femora, to A. anceps Garrison and perhaps A. fissa Selys(ligua moderately prominent, palpal setae 4, basal setae shorter thanthe remainder, and shape of female gonapophyses) (Novelo-Gutierrez1992, and pers. comm.).

This specimen has been deposited in the Museum of Zoology - InsectDivision, University of Michigan, with the database numberUMMZODO-2144.

Unfortunately, this author will not be able to travel to thiscollection area in the next year to search for additional larvaeand/or adults. I therefore urge other researchers to do so, and Iwould be able to rear larvae if the researcher is not able to. Itshould be noted that the probable dramatic changes in manysouthwestern watersheds in the US over the past 60 years may alsomake recollection of this species more difficult.

 

Acknowledgments

I graciously thank Dr. R. Novelo-Gutierrez for examining thisspecimen and bringing to my attention minute details not previouslynoticed, and John Megahan, staff artist for the Museum of Zoology,University of Michigan, for executing the drawings, and Dr. Noveloand Mr. Mark O'Brien for reviewing this paper and making suggestionsfor its improvement.

 

References

Novelo-Gutierrez, R. 1992. Biosystematics of the larvae of thegenus Argia in Mexico (Zygoptera: Coenagrionidae). Odonatologica21(1):39-71.

Westfall, M. J. 1990. Descriptions of larvae of Argia mundaCalvert, A. plana Calvert, A. tarascana Calvert and A. tonto Calvert(Zygoptera: Coenagrionidae). Odonatologica 19(1):61-70.

Westfall, M. J., and M. L. May. 1996. Damselflies of NorthAmerica. Scientific Publishers, Inc.: Gainesville, Florida, USA. x +650 p.

 


Figure 1: Dorsal view of Argia sp. specimen.


Figure 2: Detailed dorsal view of head.


Figure 3: Dorsal view of prementum.


Figure 4: Dorsal view of right metathoracic femur (upper right), withcross-sectional aspect (lower left).