Ulmeritoides acosa Ávila and Flowers, 2005

Ávila, Socorro & Flowers, R. Wills, 2005, New species and records of Ulmeritoides (Ephemeroptera: Leptophlebiidae) from Costa Rica, Zootaxa 1010, pp. 1-14 : 2-7

Ulmeritoides acosa Ávila and Flowers , new species

(Figs. 1, 2, 5, 6, 9, 10, 12, 14, 16, 18, 19, 22)

Holotype: Male imago (in alcohol). Length: body 7.3 mm; forewing, 7.1 mm. Head: light orange brown washed with black, orange–yellow spots at base of antennae and below median ocellus; antenna translucent yellowish brown, scape and pedicel washed with brown on undersides. Upper portion of eyes orange–brown, lower portion blackish. Ocelli whitish, their stalks orange washed with black. Thorax: pronotum yellowish brown, washed with black laterally and with a black streak on midline; mesonotum yellowish brown, margins and carinae darker; metanotum brown, dark brown laterally. Pleura yellowish brown washed with darker brown, a diagonal area above mesocoxae washed with black. Thoracic sterna orange–brown, washed with black. Forewing (Fig. 1): membrane hyaline, costal and subcostal area shaded with light brown, a dark brown patch on wing base; longitudinal veins and cross veins translucent brown, cross veins between costa and Rs narrowly shaded with dark brown; 7 cross veins basal to bulla. Hind wing (Fig. 2): membrane hyaline, a brown spot at base; C, Sc, and R 1 brownish, remaining veins hyaline; cross veins in costal area brown, remaining cross veins hyaline. Foreleg: coxa and trochanter brown, femur orange, washed with dark brown dorsally and on apex tibia dark brown, tarsus whitish, washed with dark brown on basal 2/3. Hind legs orange yellow with dark brown dorsal spot on apex of femora, hind femur also with two basal brownish streaks. Abdomen (Fig. 10): terga orange–brown, terga I and II heavily washed with dark brown, terga III–VIII with dark brown lateral areas and a posterior band, band narrowed medially; terga IX and X with brown apical spots at midline; terga II–IX with a pair of yellowish white anterior submedian spots each side of midline. Abdominal sterna yellowish orange washed with brown, a pair of paler spots anterioraly on each segment. Genitalia (Fig. 5): styliger plate orange–brown, forceps and penes smoky brown. Penis lobes (Fig. 6) elongate, compressed and curved dorsally, with a median triangular ventral projection. Caudal filaments orange brown, whitish apically.

Allotype: Female Subimago (in alcohol). Length: body 8.6 mm; forewing 7.3 mm. Coloration as in male imago except: head yellowish white, marked with dark brown between ocelli; antenna with scape and pedicel yellowish white, flagellum yellowish brown. Wing membrane translucent, longitudinal veins pale, crossveins brown, pale posteriorly. Legs as in male imago except forefemur with a dark patch on posterior surface. Abdomen yellowish tan with dark brown markings and pale spots as in male imago; sterna yellowish white, washed with brown on sterna I, VII–IX and with median and transverse brownish bands on sterna II–V. Subgenital plate yellowish white with dark brown lateral margins. Caudal filaments orange yellow.

Mature nymph (in alcohol): Body length 6.4–9.3 mm. Head: yellowish brown to chestnut brown, a pale spot anterior to median ocellus, and pale areas between eyes and lateral ocelli (Fig. 9). Antenna yellowish brown. Mouthparts: labrum ( Fig. 14) with maximum length slightly less than 1/2 width, anteromedian emargination well developed, denticles obsolete or very weakly developed; maxilla ( Fig. 16) with anteromedian tooth very small, galea–lacinia with inner subapical row of 13–15 pectinate setae, slightly convergent to lower border of apical setae; segment 2 of labial palpi ( Fig. 18) subequal to segment 1; segment 3 slightly less than 1/4 length of segment 2, segment 3 ( Fig. 19) with 9 denticlelike setae on inner margin and tip; clypeus, labrum, basal 2/3 and base of molars of mandibles, basal 1/2 of maxillae and segment 1 of palp and labium yellowish brown, submentum yellowish brown with 2 pale basal spots. Thorax: terga yellowish to chestnut brown, washed with black on lateral margins, pleura and sterna yellowish tan. Legs: yellowish to reddish brown, coxae washed with black; femora dark at apex, hind femur with a dark basal streak, forefemur with a dark median spot on inner surface; tibiae and tarsi yellow to orange brown, tarsi paler at base and apex; in very mature nymphs foretibiae and basal half of foretarsi dark reddish brown. Abdomen: terga yellowish to deep chestnut brown, with dark brown lateral and apical markings as in male imago (Fig. 10); sterna yellowish or orange–brown washed with darker brown. Gills gray, tracheae and fimbriae gray­violet. Caudal filaments yellowish brown, alternating segments slightly darker.

Etymology. acosa , noun in apposition. This species is dedicated to the personnel of the Area de Conservación Osa (ACOSA) in recognition of the support given to both authors during this study. The Area de Conservación Osa is also where the senior author first collected and reared this species.

Specimens Examined. (10 ♂♂, 4 ♀♀, 177 nymphs)(INBio): Male imago HOLO­ TYPE (with nymphal exuvium) labeled COSTA RICA, Puntarenas, Peninsula de Osa, La Palma , quebrada que cruza la calle a 600m del cementario después del puente carretera a Guadelupe , 25m, L_S_287000­521500, 17–I–2005, S. Ávila, R. W. Flowers. Female subimago ALLOTYPE. same data as holotype. PARATYPES: Guanacaste Province: 5 ♂, 2♀ (2 ♂, 1♀ reared with nymphal exuviae; 1 ♂ FAMU, 1 ♂ IFML) Santa Elena Peninsula , Río Mairena 2km arriba de Cuajiniquil, 21m, 10°56'N, 85°41'W, 27–I–2005, S. Ávila, R. Tiffer, R.W. Flowers; 21 nymphs, same locality, 25–I–2005, S. Ávila, M. M. Chavarría, R.W. Flowers; 34 nymphs, Río Potrero Grande , L _N_315779­351937, 21–III–2004, M. M. Chavarría D.; Nicoya Peninsula, 17 nymphs, Parque Nacional Diriá, Río Enmedio , 190m, 10°10'N, 85°06'W, 14–II–2005, S. Ávila, W. Porras, R. W. Flowers; Nandayure: 10 nymphs, Río Santa Rita , 50m, 10°01'N, 85°16'W, 17–I–2005, W. Porras; 26 nymphs (6 IFML, 6 MZUCR, 14 INBio), Maquenco, Quebrada Maquenco, 392m, 9°58'N, 85°59'W, 16–II–2005, S. Ávila, W. Porras, R. W. Flowers; 11 nymphs, Tacanis, Quebrada Pavas, 200­300m, L_N_224500­392600, 8–V–2004, W. Porras; 19 nymphs, Finca Pochote, 100– 200m, L_N_219500–347000, 7–V–2004, W. Porras; Puntarenas Province, same locality, date, and collectors as holotype: 2 ♂ imagos, 1 ♂ subimago (reared with nymphal exuviae), 27 nymphs (5 FAMU, 3 MZUCR, 13 INBio); same locality as holotype: 1 ♂ subimago, 1 ♀ subimago, 22 nymphs (3 IFML, 19 INBio), 29–VII–2004, S. Ávila; 1 nymph, 24–III–2004, S. Ávila; 10 nymphs, 9–X–2004, S. Ávila; 18 nymphs, 25–XII–2005, S. Ávila; Golfito, Río Claro , Queb. Lagarto, 40m, L_S_293100­564700, 24–II–2004, S. Ávila. Association of adults and nymphs is by rearing .

Ecology. This species is always found in masses of decaying leaves at the bottom of pools in slow–flowing streams in medium to low altitudes (less than 500m). The population at the type locality on the Osa Peninsula inhabits a deep pool on a small stream flowing through an agricultural landscape with small farms and pastures in what once was Pacific lowland rainforest. Here and elsewhere nymphs are best collected by washing them out of packs of leaves collected from the bottom of pools. At La Palma, nymphs with black wingpads have been collected from July to January. Adults of the type series were collected at blacklights and by hand along the stream banks, the first adults appearing at blacklight just after 8:00 PM. Subimagos emerged between 7:30 and 8:30 the morning after they were collected.

FIGURES 1–13. Ulmeritoides . Figs. 1,2,5,6,9,10, 12. U. acosa ; 1, wings; 2, hind wing, enlarged; 5, male genitalia; 6, pene, profile; 9, head of nymph; 10, tergites II­VII of male abdomen; 12, middle femur. Figs. 3,4,7,8,11. U. chavarriae ; 3, wings; 4, hind wing, enlarged; 7, male genitalia; 8, pene, profile; 11, tergites II­VII of male abdomen. Fig. 13. U. tifferae ; 13, middle femur

Farther north on the Nicoya and Santa Elena peninsulas, U. acosa is common to very abundant in pools of permanent and temporary streams in areas of dry forest and former dry forest. The temporary streams of Santa Elena lack water for up to five months of the year, and even during most of the rainy season there is very low current through the pools. We collected and reared nymphs in Santa Elena during the early dry season when the pools were isolated and the water level was dropping rapidly. Fairly small to full grown nymphs were present but there seems to be little chance that any but the largest attained the adult stage before the habitat completely dried. In the Río Pochote on the Nicoya Peninsula, Ulmeritoides nymphs do not appear until well into the dry season when leaf packs build up at the bottom of the pools. No nymphs are present during the rainy season when the river is subject to frequent spates (Wendy Porras, pers. comm.). However, in Río Enmedio (Parque Nacional Diriá), a permanent stream, small to full­grown nymphs were present, suggesting a extended emergence period similar to the population at La Palma.

Diagnosis. Ulmeritoides acosa can be separated from all other species of Ulmeritoides by the following combination of characters. In the imago: (1) fore wings with costal and subcostal areas shaded with brown; (2) penis lobes flattened, curved dorsally, and with ventral projection straight; (3) abdominal color pattern as in Fig. 10. In the nymph: (1) maxillary tusk very small ( Fig. 16); (2) middle and hind femora with few spines on exterior surface; (3) maxilla with subapical row of setae diverging laterally from apical setae ( Fig. 16); (4) abdomen with dark apical bands usually well defined.

We were initially inclined to view U. acosa populations in the temporary streams of the Nicoya and Santa Elena peninsulas as a different species from the population on Osa, based on their different habitats and what appear to be different life cycles. However, we found no consistent morphological differences either in the adult or nymph among the three different areas we studied. Although further studies of the biology and genetics of these populations may support dividing them into different species, we take the conservative approach here and consider them as one variable species.