Agapetus avitus Edwards

Etnier, David A., Parker, Charles R., John T. Baxter, Jr., Long, Todd M. & Drive, News Sentinel, 2010, A review of the genus Agapetus Curtis (Trichoptera: Glossosomatidae) in eastern and central North America, with description of 12 new species, Insecta Mundi 2010 (149), pp. 1-77 : 8-10

Agapetus avitus Edwards

Fig. 4a, 4b, 4c . Map 4

Agapetus avitus Edwards 1956b: 17

Type locality, stream (probably headwaters of Carr Creek, just nw of Moore Co. line) at US 41A 6 mi nw of Tullahoma, Bedford Co., TN. ( NMNH)

Diagnosis. Among species with inferior appendage length less than 4 times depth, only A. avitus (lateral view, Fig. 4a ) has the combination of a smoothly rounded tip of the inferior appendage, and segment X with dorsal margin tapering from just past mid-length to a terminal, ventral, horizontal denticle or point (may have additional denticles anteriodorsal to the terminal one). Most similar to A. hesperus , in which the inferior appendage is distinctly rhomboid, there are 3 pairs of denticles on the inferior appendages (only 2 pairs of denticles in A. avitus ), and there is a C-shaped notch on the dorsum of X between the subterminal and terminal denticle (dorsum of X smoothly convergent to base of terminal denticle in A. avitus ). Variants of A. avitus that have only one terminal denticle on each arm of X and distal denticle of inferior appendage terminal rather than subterminal resemble A. walkeri , but differ in lacking a concave area above the distal denticle of the inferior appendage, and in having distal portion of ventral arms of X and its terminal denticle horizontal (curved dorsad in A. walkeri ).

Description. Male. Length 5.5-6.6 mm (n = 6). Male genitalia: Lateral view ( Fig. 4a ), segment IX anterior margin smoothly and rather symmetrically convex to convex ventral margin; dorsal margin length of ventral margin; posterior margin sloping down and back (20 o) to upper edge of preanal appendage, then down and back at 40 o angle to mid-depth, then nearly vertical to ventral margin. Preanal appendage slender, basal 1/4 covered by posterior margin of IX, depth less than 1/4 visible length, which has 10-12 long, erect setae on dorsal edge. Sides of segment X membranous dorsally, sclerotized on ventral 1/2; ventral arms more heavily sclerotized and terminating in dark, horizontal to slightly upturned, acute denticle; additional darkened denticles often present subterminally along dorsal edge of sclerotized area, and laterally on distal 1/2 of ventral arms. Dorsally, X horizontal on basal 2/3, then sloping down to middle of terminal denticle. Inferior appendage length = 2.6 times depth; ventral margin horizontal basally, distal 1/3-1/2 sloped upward, dorsal margin convex to rounded posteriodorsal corner; posterior margin varying from smoothly and symmetrically rounded to asymmetrically rounded to bluntly pointed. Internally, a dark denticle, submarginal to marginal and slightly protruding, visible at near mid-depth; another denticle visible on ventral margin at about 3/4 length of inferior appendage.

Dorsal view ( Fig. 4b ). Segment IX anterior margin broadly U-shaped, posterior margin faint or not apparent. Sclerotized sides of X with dorsal edges parallel basally, separated by membrane throughout or only on distal 1/3-1/2; ventral arms narrow at base, converging and thickening to nearly contact at about 20 o angle near mid-length, then diverging at same angle and narrowing to often swollen base of terminal denticle; subterminal denticles (not shown in Fig. 4b ) transverse to parallel to body axis when present. Preanal appendages smoothly curved, parallel-sided, inner margins convex, tips divergent from body axis at 30 o- 40 o. Both pairs of denticles on distal 1/2 of inferior appendage (not shown) pointed, transverse.

Ventral view ( Fig. 4c ). Anterior base of IX concave, posterior base broadly V-shaped (90 o angle) between inferior appendage bases; depigmented triangular area between inferior appendage bases extends anteriad to slightly anterior to inferior appendage bases, bounded anteriad by a transverse band of setae. Inferior appendage inner base at 45 o to body axis; outer margins concave, a nearly straight longitudinal carina on basal 3/4, distal 1/2 of outer margin formed by dorsal edge of appendage; inner margins in contact at base, straight to concave and diverging from each other at 20 o angle to 2/3 length, then more divergent to pair of denticles on ventral margin, then rounded to terminal pair of denticles.

Larva. Head and pronotum light brown, other sclerites pale yellow. Details visible on intact larvae, but more so on shed sclerites. Head with oval pale area around eye and pale adjacent to vertex; darker brown muscle scars prominent on posterior 1/2, forming 3 parallel horizontal rows behind eye and scattered elsewhere. Frontoclypeus with irregular pale spot same size as eye spot posteriolateral to each eye, and with 3 equally spaced rows of transverse dark muscle scars, anterior row (middle of sclerite) and middle row with 2 scars each, posterior row (middle of posterior 1/2 of sclerite) with 5 scars. Pronotum with posterior 1/2 paler than anterior 1/2 and covered with brown muscle scars. Mesonotal sclerites each with brown freckles laterally. Metanotal sclerites same color as freckles, thus darker than adjacent membrane. Brown freckles on legs. Mesosternal sclerites tan. Legs, sterna, and sclerites on IX and X otherwise typical for genus.

Emergence dates. 9 April-20 June.

Distribution. AL Colbert (3), Franklin, Jackson (9), Lauderdale (5), Limestone, Madison (2). KY Clinton, McCreary, Trigg, Warren, Wayne (2). MS Tishomingo. TN Bedford, Decatur, Fentress (3), Franklin, Giles, Grundy, Hardin (3), Houston (2), Humphreys (3), Lawrence, Lewis, Montgomery (2), Moore, Overton (2), Perry (3), Pickett (2), Putnam (3), Stewart (2), Van Buren (2), Wayne (4), White. We consider Edwards (1966) record from “Coffee Co., Duck River at Manchester,” based on 3 larvae, to represent A. aphallus , which is abundant in that area.

Discussion. We have taken A. crasmus , A. gelbae , A. hesperus , A. illini , and A. vireo syntopically with A. avitus . Edwards (1956b) mentioned “the considerable difference in the shape and size of the inferior appendages and in the tenth tergite.” Harris (1984) further considered this situation; the holotype has a basoventral pair of denticles on X that was not present in any of the males of the 84 specimens of both sexes he examined, but denticles (or at least a darkened area) are present near that position in several of the many males we have examined. In addition to the variation noted by Harris, we have seen numerous specimens that have no other denticles on X except for the terminal pair. Inferior appendage variation in shape and relative size of the two pairs of denticles also occurs. These variants were taken with typical males, and at widely separated localities. The similarity of larvae and females with those of A. aphallus suggests that the presumably all-female A. aphallus is closely related to A. avitus . The apparently parapatric distribution (Maps 1 and 3) of the two taxa does not detract from that possibility. This is primarily a species of the Highland Rim physiographic province, with its donut-shaped distribution reflecting a strong avoidance for the Central (Nashville) Basin physiographic province, where A. aphallus occurs.

Etymology. Not mentioned in the description, but presumably based on the Latin avitus = ancestral.

Figures

Figure 4-6. Agapetus spp. male genitalia. 4) Agapetus avitus Edwards. 4a, lateral view; 4b, dorsal view, inferior appendages not shown; 4c, ventral view of IX and inferior appendages. 5) Agapetus baueri Etnier, Parker, and Baxter. 5a, lateral view; 5b, dorsal view; 5c, ventral view, preanal appendages not shown. 6) Agapetus crasmus Ross. 6a, lateral view; 6b, dorsal view; 6c, ventral view, preanal appendages not shown.