Myrmelachista

Longino, J. T., 2006, A taxonomic review of the genus Myrmelachista (Hymenoptera: Formicidae) in Costa Rica., Zootaxa 1141, pp. 1-54 : 10-14

Myrmelachista

Key to workers (costa rica)

1. Antenna with 10 segments; mesosoma strongly hourglass-shaped, with strong constriction at metanotal groove (Fig. 2); color dark brown to black....................2

- Antenna with 9 segments; mesosoma not strongly hourglass-shaped, moderately constricted at metanotal groove; color variable, from yellow orange to red brown to black....................................................................................................................3

2(1). Surface of head and mesosoma shagreened; HW greater than 0.50mm...... zeledoni

- Surface of head and much of mesosoma smooth and shiny; HW less than 0.48mm. ................................................................................................................... mexicana

3(1). Color nearly uniform light yellow orange or with some degree of infuscation on gaster (Fig. 2C); if clearly bicolored with orange head and mesosoma and dark gaster, pubescence on sides of head and on hind tibia usually abundant, suberect, OI usually less than 22............................................................................................4

- Color black to red brown, usually either uniform red brown or with dark head and gaster and mottled light and dark brown mesosoma (Fig. 2B); if clearly bicolored, pubescence on sides of head very sparse and fully appressed, pilosity on hind tibia fully appressed, and OI greater than 21................................................................10

4(3). Maxillary palpus always 6-segmented; HW of larger workers usually greater than 0.65mm...................................................................................................................5

- Maxillary palpus always 5-segmented; HW of larger workers usually less than 0.65mm (the following set of species cannot be reliably distinguished with workers but can be differentiated with queens)..............................................................6

5(4). Infuscation of gastral tergites weak, confined to posterior third or less of tergites; nests in live stems of various plants in southern mountains of Costa Rica.............. ............................................................................................................. meganaranja

- Infuscation of gastral tergites more extensive, dark brown and covering 2/3 or more of tergite; nests in one species of understory Guarea in Cordillera de Tilarán, Costa Rica.. .......................................................................................... .. flavoguarea

6(4). Gastral tergites completely yellow, without posterior band of infuscation; hind tibia with suberect pilosity ................................................................................... ...7

- Gastral tergites with variably developed infuscated band posteriorly; hind tibia with suberect or appressed pilosity.. ..................................................................... ..8

7(6). Head of larger workers relatively broad (Fig. 4), CI 98-103; Atlantic slope ........... .............................................................................................................. ... flavocotea

- Head of larger workers relatively narrow, CI 87-95; southern Pacific slope ........... ............................................................................................................. lauropacifica

8(6). Hind tibia with pilosity fully appressed.... ............................................. .. nigrocotea

- Hind tibia with pilosity subdecumbent to suberect .............................................. ...9

9(8). Side of head with projecting erect setae, the longest of which are similar in length to length of first funicular segment; Atlantic slope.. ....................... .. lauroatlantica

- Side of head with projecting setae subdecumbent, very short, much shorter than length of first funicular segment; montane areas and southern Pacific lowlands ..... .......................................................................................................... haberi and osa

10(3). Color solid black; clypeus bulging; mandible with teeth 4 and 5 (counting from apex) separated by a wide diastema, teeth 1-4 more closely and evenly spaced; HW of larger workers 0.75mm or greater .................................................. ... cooperi

- Color variable; clypeus not strongly bulging; mandible without diastema between teeth 4 and 5, all 5 teeth relatively evenly spaced; HW of larger workers usually less than about 0.70mm ..................................................................................... ...11

11(10). Head relatively elongate and subrectangular (Fig. 5), CI 89-95; mandible punctatorugose; sides of head with pubescence sparse and very short, subdecumbent to fully appressed ........................................................................................ ... longiceps

- Head relatively shorter, often somewhat cordate, CI 92-107; mandible usually smooth and shining; pubescence on side of head variable, from sparse and fully appressed to abundant and suberect (workers of plebecula and joycei cannot always be distinguished).. ................................................................................... ..12

12(11). Often bicolored, with light red brown head and mesosoma, dark gaster, but may have same coloration as joycei ; pubescence on side of head usually sparse, short, fully appressed; pilosity on hind tibia usually appressed; eyes relatively larger, OI 22-25; HW of larger workers usually less than about 0.53mm (Fig. 5)... plebecula

- Never bicolored (except nanitics), head and gaster dark brown, mesosoma variably mottled light and dark red brown; pubescence on side of head and hind tibia subdecumbent; eyes relatively smaller, OI 19-21; HW of larger workers often greater than 0.53mm.. ...................................................................................... joycei

Key to queens (Costa Rica)

1. Antenna with 10 segments; color dark brown to black..........................................2

- Antenna with 9 segments; color variable, from yellow orange to red brown to black.. ................................................................................................................................4

2(1). Mandible strongly falcate; head dorsoventrally flattened........................... cooperi

- Mandible subtriangular with differentiated basal and masticatory margin; head not strongly dorsoventrally flattened............................................................................3

3(2). Face weakly roughened or sericeous, not strongly shining; HW greater than 0.8mm ..................................................................................................................... zeledoni

- Face smooth and shiny; HW less than 0.6mm........................................... mexicana

4(1). Head orange...........................................................................................................5

- Head dark red brown to black.................................................................................9

5(4). HL greater than 1.2mm (Fig. 6)..............................................................................6

- HL less than 1.2mm................................................................................................7

6(5). Gaster solid dark brown; obligate inhabitant of understory Guarea in Cordillera de Tilarán.................................................................................................... flavoguarea

- Gaster yellow orange with narrow infuscated bands medially; non-specialist inhabitant of live stems in Cordillera de Talamanca............................ meganaranja

7(5). Sides of head and hind tibia with pilosity (pubescence or longer setae) completely appressed; HL less than 0.85mm (Fig. 6); eyes relatively large, OI greater than 30; ocelli small, OcI 4-7; generalist inhabitant of live and dead stems......................... ............................. plebecula (also keys elsewhere due to variability in head color)

- Sides of head and hind tibia with subdecumbent to suberect pilosity; HL greater than 0.85mm; eye size variable, OI 27-37; ocelli larger, OcI 6-10; specialist inhabitant of understory Ocotea .............................................................................8

8(7). Eyes relatively small, OI 27-31; HW greater than 0.8mm (Fig. 6); Atlantic slope and central Cordilleras............................................................................ flavocotea

- Eyes larger, OI 33-37; HW less than 0.8mm; southern Pacific lowlands................ ............................................................................................................. lauropacifica

9(4). HW less than 0.7mm (Fig. 7); generalist inhabitant of live and dead stems............ ................................................................................................................... plebecula

- HW greater than 0.7mm; specialist or generalist inhabitant of live stems...........10

10(9). HL usually between 0.8-1.2mm (Fig. 7); head relatively broad, CI 87-98; eyes relatively small, OI less than 30, often around 27 (Fig. 8); ocelli very small, OW often less than 0.05mm; mandible smooth and shining or weakly rugose; maxillary palpus always 6-segmented (workers brown to mottled red brown; common cloud forest species nesting in many species of trees)................................... joycei

- HL between 0.8-1.4mm; CI 79-93; OI 23-33; OW 0.04-0.10mm; mandible punctatorugose; maxillary palpus 5 or 6-segmented....................................................11

11(10). HW greater than 1.1mm (Fig. 7); head relatively broad, CI 88-93; eyes relatively small, OI 23-27 (Fig. 8); much of face slightly roughened, dull, not strongly shining(Fig. 9A).. .......................................................................................... nigrocotea

- HW less than 1.1mm, if approaching 1.1mm then head relatively elongate (CI less than 86); OI greater than 27; most of face smooth and strongly shining.. ......... ..12

12(11). In full face view with long erect setae projecting from sides of head (Fig. 9D); maxillary palpus 5-segmented... lauroatlantica

- Sides of head with short appressed to suberect pubescence, no longer erect setae; maxillary palpus 5 or 6-segmented.. .....................................................................13

13(12). Workers dark red brown ( longiceps queens bridge the morphological gap between haberi and osa and cannot be distinguished from either).. ........................ longiceps

- Workers yellow orange... ...................................................................................... 14

14(13). Maxillary palpus 5-segmented; CI 83-89; HL 1.00-1.12; sides of head rounding more gradually into rear margin (Fig. 9B) ...................................................... haberi

- Maxillary palpus 6-segmented; CI 79-84; 1.18-1.23; head more sharply rectangular, sides flat and more abruptly rounding into flat rear margin (Fig. 9C) .......... osa

Key to males (Costa Rica)

The male of M. osa is unknown.

1. Antenna with 11 segments; apodeme of penial valve meeting dorsal margin of blade at nearly right angle (Fig. 10A) .................................................................. ...2

- Antenna with 10 segments; apodeme of penial valve rounding into dorsal margin at obtuse angle (Fig. 10B)...4

2(1). Pygostyles absent .................................................................................... ... mexicana

- Pygostyles present.. .............................................................................................. ..3

3(2). Paramere broadly triangular ...................................................................... ... cooperi

- Paramere more elongate, with parallel sides before bluntly rounded apex .............. .................................................................................................................. ... zeledoni

4(1). Basiparamere lobe absent or reduced to short triangular tooth, much shorter than paramere; cuspis absent ....................................................................................... ...5

- Basiparamere lobe well developed; cuspis present or absent .............................. ...6

5(4). Ocelli small, width of median ocellus less than distance between median and lateral ocellus (Fig. 11A); petiolar dorsum with few to no erect setae .......... plebecula

- Ocelli large, width of median ocellus greater than distance between median and lateral ocellus (Fig. 11B); petiolar dorsum with conspicuous tuft of erect setae ...... ............................................................................................................. lauropacifica

6(4). Pygostyles present; basiparamere lobes and parameres very long and thin (Fig. 12A, B) ................................................................................................................ ...7

-. Pygostyles absent or reduced to tiny unsclerotized remnants; basiparamere lobes and parameres thin or broad ................................................................................ ...8

7(6). Digitus evenly tapered to apex (Fig. 12B)............................................. flavoguarea

- Digitus broadening apically to paddle-shaped apex (Fig. 12A).......... meganaranja

8(6). Digitus greatly expanded distally and with thickened posterodorsal and posterior margins, forming a bulla at apex (Fig. 12C, D)......................................... longiceps

- Digitus evenly tapered or scimitar-shaped, never forming a bulla at apex.............9

9(8). Cuspis absent or reduced to sharply triangular or spine-like process, closely appressed to inner surface of paramere and distant from digitus.........................10

- Cuspis present and subrectangular, separated from inner surface of paramere, apex sometimes approaching or touching dorsal margin of digitus..............................12

10(9). Digitus scimitar-shaped (Fig. 10B); cuspis present as a spiniform tooth; maxillary palpus always 6-segmented............................................................................ joycei

- Digitus more evenly tapered from base to apex; cuspis as above or absent; maxillary palpus 5 or 6-segmented................................................................................11

11(10). Maxillary palpus 5 -segmented; cuspis present as a small triangular or spiniform tooth ........................................................................................................................ haberi

- Maxillary palpus 6-segmented; cuspis absent..................................... lauropacifica

12(9). Paramere thin and evenly tapered...................................................... lauroatlantica

- Paramere scimitar-shaped, broadening apically...................................................13

13(12). Basiparamere lobe and paramere very long and thin; digitus rounded apically....... ................................................................................................................... longiceps

- Basiparamere lobe and paramere broad at the base, shorter; digitus tapering to a point at apex..........................................................................................................14

14(13). Ocelli relatively large, width of median ocellus usually greater than distance between median and lateral ocellus; distance between lateral ocelli about equal to distance from lateral ocellus to compound eye (Fig. 11C)..................... flavocotea

- Ocelli relatively small, width of median ocellus usually less than distance between median and lateral ocellus; distance between lateral ocelli less than distance from lateral ocellus to compound eye (Fig. 11D)............................................. nigrocotea