Perlidae - The Stones

Introduction

[under construction] Perlidae are generally our largest predacious stoneflies, and are especially common in cool to cold streams or rarely in wind-swept portions of clean lakes. Most species in Michigan are semi-voltine, especially towards the north, although some taxa that occur in clean warmer streams (e.g., Perlinella, Attaneuria, Neoperla, Perlesta) are probably univoltine in our area. Paragnetina media, on the other hand, appears to be broadly tolerant of most river conditions, and is probably our most common perlid.

Adults (adapted from Poulton and Stewart 1991, Stark and Gaufin 1976)

1a	Ab9 sternite produced posteriorly and recurved upward to that Ab10  is mostly or completely concealed	Males, 2
	Some species with a disk-like posteromedial structure on Ab9 sternite (hammer)
	Ab8 sternite not notched in the middle, or produced posteriorly over Ab9
1b	Ab9 sternite poorly or not produced posteriorly over Ab10, which is always visible	Females, 8
	Posterior margin of Ab8 sternite medially notched or produced posteriorly over Ab9
2a(1a)	Genital hooks developed from the hind margin of Ab10 tergum, and originating anterior to the cerci	3
2b	Genital hooks developed from the paraprocts, and originating below the cercal bases	5
3a(2a)	Two ocelli	Neoperla Needham
3b	Three ocelli (anterior ocelli in Perlinella, especially P. ephyre (Newman) may be considerably reduced)	4
4a(3b)	a. Genital hooks long, extending to the anterior margin of Ab8 tergum	Agnetina Klapálek
	b. Thoracic sterna with transverse bands of dark pigmentation
4b	a. Genital hooks shorter, extending at most to the middle of Ab9 tergum	Paragnetina media (Walker)
	b. Thoracic sterna without transverse bands of dark pigmentation
5a(2b)	Ab9 sternum without a hammer	Perlesta Banks
5b	Oval-shaped hammer present on Ab9 sternum as a low callus	6
	also: Ab10 tergum without a distinct mesal tergite although there may be some areas of darker or lighter sclerotization
6a(5b)	a. Hind corners of head angulate, eyes set far forward	Perlinella Banks
	b. Aedeagus of male with a prominent pair of lateral sclerites
	c. Forewing length < 15 mm
6b	a. Hind corners of head not angulate	7
	b. Aedeagus of male not as above
	c. Forewing length > 15 mm
7a(6b)	Ab9-10 terga with spinule patches	Acroneuria Pictet
7b	Ab9-10 terga without spinule patches, a few spinules or thick setae may be present on Ab10	Attaneuria ruralis (Hagen)
	also: Generally round in medium to large-sized rivers
8a(1b)	Two ocelli	9
8b	Three ocelli	10
9a(8a)	a. Subgenital plate broadly bilobed, with a somewhat rectangular median emarginated notch	Perlinella Banks (in part)
	b. Spermathecum membranous, usually 4 short vaginal accessory glands present
	c. Fore wing with crossveins between A1 and A2
	also: Hind corners of head angulate, eyes set far forward; body shape elongate
9b	a. Subgenital plate not produced or produced and truncate to emarginate, but not as above	Neoperla Needham
	b. Spermathecum lined with golden brown spermathecum, vaginal accessory glands absent
	c. Fore wing without crossveins between A1 and A2
	also: Hind corners of head evenly rounded, eyes set normally; body shape not elongate
10a(8b)	a. Subgenital plate not produced	Acroneuria Pictet (in part)
	also: Spermatheca narrowly cylindrical, vagina without accessory glands
10b	a. Subgenital plate slightly to strongly produced	11
11a(10b)	a. Small species, fore wing length < 13 mm	Perlesta Banks
	b. Subgenital plate notched, overlapping 1/3 of Ab9 sternum, or margin sinuate
11b	a. Larger species, fore wing length > 13 mm	12
	b. Subgenital plate variable
12a(11b)	Subgenital plate with a submarginal tubercle	Attaneuria ruralis (Hagen)
12b	Subgenital plate without a submarginal tubercle	13
13a(12b)	Fore wing with one or several crossveins between A1 and A2, thus forming two or more closed cells	Perlinella Banks (in part)
	also: Eyes set far forward, hing corners of head somewhat angulate; subgenital plate broadly bilobed, with a somewhat rectangular median emarginated notch; spermathecum membranous, with 6 vaginal accessory glands present
13b	Fore wing with no crossveins between A1 and A2, thus having only 1 anal cell	14
14a(13b)	Ab8 subgenital plate large, broadly rounded, produced to cover roughly 1/2 of Ab9 sternum, and rarely with a slight notch	Agnetina Klapálek
14b	Ab8 subgenital plate small, with a U-shaped notch, produced to cover only about 1/5 or less of Ab9 sternum	Paragnetina media (Walker)

Mature nymphs (adapted from Stewart and Stark 2000)

1a	Occiput of head with at least a partial row or ridge of closely-set setae extending to the area of the ecdysial suture	2
1b	Occiput without a setal row as above, although a few setae (2-5) may occur near the postocular fringe	6
2a(1a)	Two ocelli	Neoperla Needham
2b	Three ocelli, although the anterior ocellus may be small	3
3a(2b)	Occiput with row absent, but setae separated by irregular gaps, or clustered 2-3 deep in areas	Perlesta Banks
3b	Occiput with a close-set, single row of setae extending from the postocular fring to the ecdysial suture	4
4a(3b)	a. Anal gills present	Agnetina Klapálek
	b. Basal cercal segments bare, without an inner fringe of long silky setae
	also: Posterior setal fringe of Ab7 sternum complete mesally
4b	a. Anal gills absent	5
	b. Basal cercal segments with an inner fringe of long, silky setae
5a(4b)	a. Pronotum fringed laterally and posteriorly with short, stout bristles interspersed with a few long bristles	Paragnetina media (Walker)
	b. Occipital setae forming a closely set, complete single regular row
5b	a. Pronotum completely fringed laterally and (especially) posteriorly with long, slender bristles	Attaneuria ruralis (Hagen)
	b. Occipital setae forming a complete, but irregular, setal row
6a(1b)	a. Postocular fringe reduced to 1-2 long setae	Perlinella Banks
	b. Pronotal fringe consists of 2-5 slender bristles at the posterolateral and anterolateral angles
	also: Dorsum of body covered with fine, dark clothing hairs and scattered bristles; subanal lobe gills present; position of eyes set anteriorly well forward; median ocellus may be considerably reduced or absent
6b	a. Postocular fringe with a closely set row of several thick setae	Acroneuria Pictet
	b. Pronotal fringe consisting of stout bristles in a closely set row, sometimes incomplete laterally
	also: Three well-developed ocelli; dorsum of head mostly brown, frequently with a yellow W-shaped mark anterior to the median ocellus

Species Descriptions

Paragnetina media (Walker)

Stark and Szczytko (1981) provided a more recent description of this species, the only one of five Nearctic species found in Michigan. This species is more or less found throughout the state in most warm and cold running waters.

     Male. Body: Body length 11-16 mm; forewing 14-16 mm. General color dark brown. Abdomen: Terga 7-8 with mesal sclerites; spinule patches typically present on terga 6-9; sterna 3-8 with mesal patches of long setae; pleura 6-9 typically with lateral brushes; apical section of aedeagus strongly armed ventrally, laterally with prominent, sharply pointed, triangular spines; largest spines long and slender, located in the apical third of the aedeagus.
     Female. Body: Body length 21-24 mm; forewing 22-25 mm. General color dark brown. Abdomen: Sternum 8 with a small triangular subgenital plate; notch deep, broadly U-shaped; lateral margins of vagina constricted basally; dorsal surface lined mesally with small scale-like setae; vaginal accessory glands short; spermathecum membranous, with 3 accessory glands typically present.
     Nymph. Body: Total length of mature nymph 15-25 mm (length of females > males). General color dark brown patterned with yellow. Head: Brown except for 5 small circular areas of light pigmentation around the ocelli and tentoria. Mouthparts and setal patterns typical of genus. Abdomen: Dorsum unpatterned.
     Egg. Outline oval, cross-section circular; chorion completely sculptured with a network of raised reticulation; collar long, slender and covered with irregular longitudinal ridges giving a twisted appearance; margin weakly and irregularly incised; micropyles small, arranged circumlinearly near the equatorial area; accessory micropylar structures consist of dorsally located shallow pits.

References

Poulton BC, Stewart KW. 1991. The stoneflies of the Oaark and Ouachita Mountains (Plecoptera). Memoirs of the American Entomological Society 38. ii + 116 pp.
Stark BP, Guafin AR. 1976. The nearctic genera of Perlidae (Plecoptera). Miscellaneous Publications of the Entomological Society of America 10(1):1-77.
Stark BP, Szczytko SW. 1981. Contributions to the systematics of Paragnetina (Plecoptera: Perlidae). Journal of the Kansas Entomological Society 54(2):625-648.
Stewart KW, Stark BP. 2002. Nymphs of North American stonefly genera. Second Edition. The Caddis Press: Columbus, Ohio. xii + 510 p.

Page created: November 16, 2003 - Last updated: September 27, 2006 (EB)