Podmosta obscura (Frison)

Stewart, Kenneth W. & Stark, Bill P., 2011, Further Descriptions Of Western North American Podmosta Larvae And Their Separation From Ostrocerca Larvae (Plecoptera: Nemouridae), Illiesia 7 (10), pp. 104-117 : 110

Podmosta obscura (Frison)

( Figs. 1 , 4, 6, 7, 13-16 , 18 , 26 , 31 , 47, 48 )

Distribution. Pacific Northwest (Oregon, Washington).

Material Examined. Oregon: Benton Co., Outgate Beck intermittent stream, 60 th Street , outskirts of Corvallis , Feb. 1997 -1999 benthos and emergence trap samples, numerous individuals of all stages, specifically 6♂, 10♀, 8♂ larvae, 3♀ larvae (only adults of this species collected in emergence traps in this stream over several years by N.H. Anderson) .

Characters. Body length ♂ 4.5-5.2 mm, ♀ 5.4-5.6 mm, light brown above with mottled dark head pattern and light mesal stripe on thorax ( Fig. 1 ). Antennal segments approximately 46, head capsule width ♂ 0.90-0.96 mm, ♀ 0.96-1.02 mm; eyes large, head wider than pronotum ( Fig. 1 ). Gills absent. Mandibles with 5 or 6 apical teeth; right mandible as described herein for P. weberi , with raised molar pad that grinds against the opposing depressed molar cup of left mandible ( Figs. 21, 22 ), molar cup with outer (dorsal) comb of curved teeth ( Figs. 20, 22 ). Laciniae triangular, palmate, with scalloped palm surface, 7-9 fingerlike apical teeth, apicodorsal comb of about 10 long, acute-pointed bristles and apicoventral comb of about 8 short, acute-pointed bristles ( Fig. 26 ). Pronotum bearing scattered short bristles and sensillae on disc, distinct lateral fringe lacking ( Fig. 31 ). Wingpads bearing scattered short bristles over surface, and tuft of short bristles on anterolateral corners ( Fig. 1 ). Femora bearing scattered short bristles and hairs over dorsal surface, longer bristles apicodorsally ( Fig. 1 ). Tibiae bearing scattered short bristles and few (5-7) posterior silky fringe hairs ( Figs. 1 , 4 ). Mesosternal Y-ridge faint, closed by anterior ridge forming a rectangular area as in Stewart & Stark (2002, Fig. 9.16E ). Abdominal terga bearing scattered microtrichia and macrotrichia scattered on intercalary surface, and forming a posterior fringe. Sexual dimorphism evident; males with developing hypoproct on sternum 9 ( Fig. 14 ) and in pharate individuals evidence of developing external genitalia ( Fig. 13 ) and raised tergum 10 ( Fig. 15 ). Cercal segments 22-24; cercomeres 1-10 bearing apical whorls of stout bristles, fine hairs and sensillae, bristles about 0.65 times length of their segment ( Fig. 47 ). Middle and anteapical cercomeres bearing whorl bristles 0.35-0.46 times length of their segment, and 3-7 fine intercalary hairs about 0.32 times length of their segment, all as seen laterally ( Fig. 48 ). Diagnostic characters: cercal setation as described ( Figs. 47, 48 ).

Figures

Fig. 1. Male Podmosta obscura larva. Scale line = 2 mm.

Figs. 2-16. Podmosta larval characters. P. delicatula. 2. head, thorax, dorsal. 3. right front leg, dorsal. 5. cercus, lateral. 9. male terminalia, dorsal. 10. male terminalia, ventral. 11. male terminalia, lateral. 12. female terminalia, dorsal. P. obscura. 4. right front leg, dorsal. 6. right cercus proximal segments, dorsal. 7. left cercus apical segments, lateral. 13. male terminalia, dorsal. 14. male terminalia, ventral. 15. male terminalia, lateral. 16. female terminalia, ventral. P. weberi. 8. right cercus, lateral (exuvium of reared male). 12a. male terminalia, ventral (exuvium of reared male).

Figs. 17-22. Podmosta mandibles. 17. P. delicatula left mandible, ventral. 18. P. obscura left mandible, ventral. 19. P. weberi right mandible, ventral. 20. P. weberi left mandible, ventral. 21. P. weberi right molar pad. 22. P. weberi left molar cup.

Figs. 23-28. Ostrocerca and Podmosta mandibles and laciniae. 23. O. dimicki right mandible, ventral. 24. O. dimicki left mandible, ventral. 25. P. decepta lacinia, ventral. 26. P. obscura lacinia, ventral. 27. P. weberi lacinia, ventral. 28. O. dimicki lacinia, galea, ventral.

Figs. 29-34. Podmosta and Ostrocerca pronota. 29. P. decepta, right disc. 30. P. delicatula, right disc. 31. P. obscura right disc. 32. P. weberi left disc. 33. O. dimicki left disc. 34. O. dimicki left anterolateral disc margin.

Figs. 47-52. Podmosta and Ostrocerca cerci. 47. P. obscura proximal cercomeres. 48. P. obscura subapical cercomeres. 49. P. weberi cercomere 10. 50. P. weberi cercomere 20. 51. O. dimicki cercomeres 10, 11, 52. O. dimicki cercomere 15.