Keys to the Costa Rican species of paper wasps ( Hymenoptera : Vespidae : Polistinae )

Paper wasps (subfamily Polistinae) are one of the four main groups of eusocial insects in the Neotropics. They are medically important for the frequent stings inflicted on humans, but at the same time are valuable predators of pest insects. Nonetheless, there are no updated keys for the identification of the Central American species. Here we provide keys to the 18 genera and 106 species known to occur in Costa Rica, illustrated with one hundred original line drawings.


Introduction
In the Neotropics most wasp stings are due to paper wasps, yet these wasps are important predators of other insects and can be useful in biological control. They are one of the four main groups of eusocial insects present in the region (along with stingless bees, ants, and termites) and they derive their name from the fact that their nests consist predominantly of masticated wood fibers (Wenzel 1998). There is a considerable amount of literature on the biology of paper wasps, much of which was reviewed by West-Eberhard, Carpenter, & Hanson (2006). Despite their importance and interesting biology, the only published keys currently available for identifying the Costa Rican species are those of Richards (1978), which are for the entire New World and often difficult to use. The objective of this paper is to provide more accessible keys for identifying the 106 described species of Polistinae known to occur in Costa Rica.

Results
The keys include all 18 genera and the 106 named species currently known to occur in Costa Rica (Table 1). It should be noted that while we have attempted to make the keys useable by a nonspecialist, there are a few species that remain difficult to identify, requiring experience and sometimes comparison with identified specimens. The keys should be useful for identifying paper wasps in Nicaragua and Panama, but they will be less useful in more distant countries. Key to the Costa Rican Genera of Polistinae 1. Propodeal orifice dorsally acute, T1 evenly conical in dorsal view (Fig. 1). [Pronotal carina posterior to the fovea (Fig. 2); medium sized to large wasps, WL > 10 mm; nest is an exposed, stalked comb.] Polistes -Propodeal orifice usually broadly rounded dorsally (Fig. 3). T1 differently shaped: sessile with width greater than length (Fig. 4), long and narrow (Fig. 5) or basally petiolate (Fig. 6).. 2 2. Mid and hind tarsus with third and fourth segments asymmetrical, with inner lobe longer than outer lobe (Fig.  7). T1 petiolate: in dorsal view with width half or less that of T2 and at least twice as long as wide (Fig. 8). Nest is an exposed, stalked comb Mischocyttarus -Mid and hind tarsus with third and fourth segments symmetrical. T1 variously shaped. Nest nearly always covered with an envelope, but if not then it is much larger (Apoica) or in a cavity (Agelaia) 3 3. Pronotum without lateral fovea 4 -Pronotum with lateral fovea (Fig. 9), sometimes shallow 8 4. Scutellum angled in profile, metanotum vertical in profile (Fig. 10). Occipital carina present dorsolaterally.
[Nest usually very large, 40-50 cm in diameter.] Brachygastra -Scutellum rounded in profile, metanotum not vertical in profile, but rather curving anteriorly towards scutellum (Fig. 11). Occipital carina absent 5 5. Body completely black or blue (except in the rarely collected Synoeca chalibea which is reddish brown ventrally), with virtually no yellow markings. WL 8-20 mm. Nest either hanging from branch, or lying flat on substrate and usually greater than 10 cm long 6 -Body usually with at least some yellow markings. WL usually about 6-8 mm. Nest lying flat on substrate, usually less 10 cm long; envelope with transparent spots 7 6. Body shining black; WL 8-11mm. Base of fore coxae distended (Fig. 12). Nest usually hanging from a branch Epipona -Body with blue reflections, ranging from completely bluish black to barely a few blusih reflections; WL 17-20 mm. Base of fore coxae not distended. Nest lying flat on substrate Synoeca 7. Body very robust; T1 short and broad, length < 2 x posterior width. Gena very narrow, ˂ 0.5 x eye width (Fig.  13). Propodeum deeply excavated. Face reddish brown Clypearia naumanni -Body more elongate; T1 very long, length > 3 x posterior width. Gena > 0.5 x eye width. Propodeuum not deeply excavated. Face mostly black Metapolybia 8. Mesepisternum with complete dorsal groove (Fig. 14) 9 -Mesepisternum with dorsal groove absent or only represented by partial anterior trace 11 9. Ocelli enlarged, separated from eyes by less than an ocellar diameter (Fig. 15). Nest a flat, circular comb without an envelope, attached to a twig Apoica -Ocelli normal, separated from eyes by more than an ocellar diameter. Nest covered with an envelope, or if not, then located in a cavity (most Agelaia) 10 10. Scutum with posterolateral lamella present anteriorly, adjoining tegula (Fig. 16). Very common. Nest often hidden in hollow tree.
Agelaia -Scutum with posterolateral lamella absent anteriorly. Uncommon. Nest envelope like an inverted flask. [Body yellow and brown.] Angiopolybia zischkai 11. Pronotal carina curving sinuously as it runs down the sides (Fig. 17). Fore wing with prestigma about as long as pterostigma (Fig. 18) Parachartergus -Pronotal carina not curving sinuously as it runs down the sides (Fig. 9). Fore wing with prestigma shorter than pterostigma ( (Fig. 28). Usually with yellow markings on metanotum, propodeum and posterior margin of T1-T2 P. pacificus -Occipital carina strong and reaching all the way down to the mandibles (Fig. 29). Propodeum and metasoma usually without yellow markings 4 4. T1 (in lateral view) sloping up at an angle of about 70° (Fig. 30). Lower clypeus reddish brown. WL 18-19 mm P. bicolor -T1 sloping up more gradually at an angle of about 45° (Fig. 31). Lower clypeus mostly black. WL 16-17 mm P. deceptor 5. Mesosoma and metasoma completely black in dorsal view 6 -Mesosoma and metasoma at least with some reddish (or yellowish) brown in dorsal view 9 6. Propodeum with weak striae, not extending to the sides (Fig. 26). [Body black with bluish reflections. Nest is a vertical chain of cells.] P. goeldii -Propodeum with strong striae extending to the sides (as in Fig. 25 Sides and venter of mesosoma, coxae and often femora, mostly black 10 -Sides and venter of mesosoma, and legs, mostly reddish (or yellowish) brown14 10. Scutum all black and with erect hairs that are almost as long as the ocelar diameter ( Fig. 32)  P. testaceicolor -Propodeum with distinct striae (Fig. 25). Mesepisternum without epicnemial groove or with only a faint groove 15 15. Scutum reddish brown contrasting with dull yellow propodeum, metasoma with contrasting bands of reddish brown and dull yellow 16 -Dorsal surface of body more uniformly reddish brown 17 16. Malar space longer than wide (Fig. 37). Propodeal striae almost extending to border with metapleuron (Fig.  25). WL 20-28 mm P. carnifex -Malar space not longer than wide (Fig. 38). Propodeal striae variable, limited to central area or extending to border with metapleuron. WL 16-21 mm P. major 17. Area behind ocelli pale yellow, in contrast to rest of body. Wings yellowish to reddish brown P. infuscatus -Area behind ocelli reddish brown, like rest of body. Wings darkerP. canadensis Key to species of Mischocyttarus 1. Body black, fore wing black with whitish apex M. deceptus -Body black or differently colored, fore wing never black with whitish apex 2 2. Fore and mid femur with a distinct ventral groove near base, delimiting a small ring (Fig. 39).
[Large, WL 15-20 mm; body dark brown.] 3 -Fore femur without, mid femur rarely with traces of such a groove 5 3. T1 about 3 x as long as wide at posterior margin (Fig. 40); tibiae and tarsi yellowish, contrasting with brown body M. carbonarius -T1 about 6-7 x as long as wide at posterior margin (Fig. 41); tibiae and tarsi brown like rest of body 4 4. Pronotal keel continuous throughout, central part not concealed by hairsM. labiatus -Pronotal keel weak in center, partially concealed by hairs (especially in dorsal-posterior view) M. melanarius 5. Pronotum without fovea and sides of mesosoma with extensive yellow or reddish brown 6 -Pronotum with fovea (Fig. 42); if fovea weak and difficult to see (M. tolensis) then sides of mesosoma black 9 6. Lateral and ventral parts of mesosoma, and legs, with extensive reddish brown. Head quite stout in dorsal view, mesosoma extensively punctate M. chalucas -Mesosoma and legs yellow with black markings, without reddish brown. Head less stout in dorsal view, mesosoma not noticeably punctate 7 7. Anterior margin of pronotum strongly raised and with 3 "windows" (Fig. 43), this flange visible laterally and ending in a pointed lobe. Pronotal keel curved backward at sides. Male antenna with last segment expanded and truncate M. collarellus -Anterior margin of pronotum not so strongly raised, without 3 "windows", and not ending in a pointed lobe. Pronotal keel straight in dorsal view. Male antenna with last segment narrow, cylindrical 8 8. Anterior margin of pronotum more strongly raised and followed by a deep furrow with an acute hind margin. Clypeus with apex bidentate (Fig. 44).
M. nigroclavatus -Anterior margin of pronotum less raised and followed by a shallow furrow with an obtuse hind margin. Clypeus not bidentate at apex. M. cleomenes 9. Mid tarsus with segment 3 hardly asymmetrical (Fig. 45) (Fig. 47). S2 usually without clearly differentiated tridentate black spot at base. Mid and hind tibiae and femora usually without sharply contrasting dark stripes M. mexicanus -Pronotal carina forming a raised shoulder (Fig. 48). S2 usually with clearly differentiated tridentate black spot in anterior half. Mid and hind tibiae and femora usually with sharply contrasting dark stripes on yellow background 16 16. Anterior margin of pronotum strongly raised, followed by a deep furrow whose hind margin is acute or lamellate (Fig. 49). Frons with one large yellow spot (Fig. 50) M. basimacula -Anterior margin of pronotum little raised, followed by a feeble furrow whose hind margin is obtuse (Fig. 51). Frons with 3 smaller yellow spots, 1 above and 2 below (Fig. 52) 2 -Pronotal carina strong to weak, but always evident (in dorsal view) 3 2. Anterior margin of lateral pronotum with a very wide lamella (Fig. 53)A. pleuralis -Anterior margin of lateral pronotum with a very narrow lamella (Fig. 54)A. cajennensis 3. Lateral margin of pronotal carina protruding and angular (Fig. 55). Blackish brown, without yellow markings except sometimes on legs. Sides of T1 divergent posterior to spiracles. WL 12-18 mm 4 -Lateral margin of pronotal carina less protruding and more rounded (Fig. 56). If mostly black colored (A. xanthopus), then WL 10-12.5 mm and T1 subrectangular posterior to spiracles 5 4. Tibiae and tarsi entirely yellow A. angulicollis -Tibiae and tarsi black or blackish brown, fore and mid tibiae sometimes with a yellowish stripe in males A. panamaensis 5. Pronotal carina very strongly raised in front of fovea, curving around it and fading as it curves, leaving the fovea at the bottom of a deep hollow (Fig. 57). Body blackish brown, usually without or with very few yellow markings A. xanthopus -Pronotal carina not very strongly raised in front of fovea. Body usually with more yellow markings 6 6. T4-T6 entirely black or dark brown 7 -T4-T6 with yellow posterior bands, or metasoma mostly brownish orange 8 7. Eyes with short hairs. T1-T3 usually dark colored (with yellow bands), sides of T1 dark A. yepocapa (in part) -Eyes without or with very few short hairs. T1-T3 light brown (with yellow bands), sides of T1 usually bright yellow A. melanopyga 8. All terga brownish orange (posterior terga sometimes darker), without or with very narrow, almost inconspicuous posterior yellow bands. Eyes without or with very few short hairsA. centralis -Terga black or dark brown, at least T2-T3 with conspicous yellow bands. Eyes with short hairs 9 9. Dorsal pronotal carina more raised at sides. T1 subquadrate behind spiracles in workers and males (Fig. 58), subsessile in queens. Yellow bands on terga about 1/4 to 1/3 as broad as the tergum A. areata -Dorsal pronotal carina less raised at sides. T1 longer, subrectangular or with sides divergent after spiracles (Fig. 59). Yellow bands on terga about 1/6 to 1/5 as broad as the tergumA. yepocapa (in part) Key to species of Apoica 1. Metasoma light brown with pale posterior bands on some terga A. strigata -Metasoma uniformly colored, without transverse bands on dorsal surface 2 2. Dorsal surface of metasoma entirely pale yellow to white A. pallens -Dorsal surface of metasoma dark colored 3 3. Last metasomal tergum entirely pale or with pale colored triangle (Fig. 60). Eye with prominent hairs present over entire surface (Fig. 61) A. pallida -Last metasomal tergum rarely with strong pale color, occasionally with faint pale color on posterior tip of tergum, but not triangle-shaped. Eye bare or with just a few hairs A. thoracica* * A. ellenae from Barro Colorado Island, Panama, is similar to A. thoracica, but has a fine pubescence that generates a silvery-gray sheen over the meso-and metasoma. Key to species of Brachygastra 1. Top of head and scutum with yellow markings B. smithii -Top of head and scutum completely dark colored 2 2. Scutellum yellow, junction of dorsal and posterior surfaces rounded (Fig. 62)B. scutellaris -Scutellum black, with a marked angle between dorsal and posterior surfaces (Fig. 63) 3 3. Head and mesosoma without golden pubescence, wings transparent. Mesosoma coarsely punctured. WL 6 mm B. augusti -Head and mesosoma with golden pubescence, wings yellowish orange and with dark tips. Mesosoma less coarsely punctured. WL 7.5 mm 4 4. Scutellum in dorsal view usually emarginate posteriorly (Fig. 64)B. lecheguana* -Scutellum in dorsal view not or little emarginate posteriorly (Fig. 65)B. mellifica* * The only reliable way of separating B. lecheguana from B. mellifica is on the basis of the male genitalia (Naumann, 1968). Key to species of Chartergellus -Frons with 3-pointed reddish brown mark, with the central point nearly reaching the median ocellus (Fig. 66); area immediately above mandible predominantly whitish C. golfitensis -Frons with reddish brown mark that is not 3-pointed, dorsal central part usually closer to antennal insertion than to median ocellus (Fig. 67) (Fig. 73) 3 3. Pronotal carina where it passes down the sides distinctly curved (Fig. 74). WL = 12-13 mm P. apicalis -Pronotal carina where it passes down the sides barely curved (Fig. 75). WL = 10-11 mm P. aztecus Key to species of Polybia 1. Predominanly light orangish brown, or with extensive yellow markings; sides of mesosoma and coxae mostly light colored 2 -Predominantly black or dark brown, including sides of mesosoma and coxae; if yellow markings are present, then these are quite limited 5 2. Scutum with short erect hairs, their length equal to about half the diameter of the ocellus (Fig. 76). Metasoma black with yellow bands P. emaciata -Scutum without erect hairs, or hairs much shorter. Metasoma generally orangish brown with yellow bands 3 3. Length of T1 about 2 x posterior width (Fig. 77). Propodeum with central groove that widens posteriorly. WL = 9-10 mm P. nidulatrix -Length of T1 > 2 x posterior width (Figs. 78-79). Propodeum without evident central groove, or with incomplete groove. WL = 6-8 mm 4 4. T1 with spiracular area barely or not projecting, not forming a concavity behind spiracle (Fig. 78). Pronotum without trace of carina. Color usually light brown P. bistriata -T1 with spiracular area clearly projecting and forming a small concavity right behind spiracle (Fig. 79). with slight trace of dorsal carina. Color paler, predominantly yellowish P. selvana 5. Fore wing with anterior margin orangish brown, black at tip P. rejecta -Fore wing variable in color, if anterior margin orangish brown (P. flavitincta) then without black tip 6 6. Propodeum with punctures and/or scutum with erect hairs about as long as half the diameter of the ocellus.
[Mesosoma and metasoma without any yellow.] 7 -Propodeum without punctures, scutum without erect hairs or hairs much shorter 11 7. Scutum without erect hairs. T1 ˂ 1.4 x as long as posteriorly wide P. simillima -Scutum with erect hairs. T1 at least 1.5 x as long as posteriorly wide 8 8. Pronotal carina absent or very weak. Larger than most other Polybia, WL at least 12 mm P. flavitincta -Pronotal carina evident. WL <12 mm 9 9. T1 with numerous distinct punctures and > 2 x as long as posteriorly wideP. tinctipennis -T1 without distinct punctures and 1.5 to 1.8 x as long as posteriorly wide 10 10. Head and mesosoma with very dense fine sculpture, without any shining surface. Basal cell of fore wing blackened throughout (Fig. 80). Anterior central propodeum with much denser hairs than rest of propodeum P. ignobilis -Head and mesosoma finely reticulate, but somewhat shining. Basal cell blackened primarily at apex (Fig. 81). Propodeum with uniformly scattered hairs P. raui 11. T1 about 1.5 x as long as wide at posterior margin, or less (Figs. 82-83) 12 -T1 > 1.5 x as long as wide at posterior margin (Figs. 84-87) 13 12. Body all black. Propodeal valvula narrow and almost parallel-sided ( Fig. 88)P. bifasciata -Metanotum and propodeum with yellow. Propodeal valvula broadly triangular (Fig. 89) P. barbouri 13. Eyes with scattered short hairs. All black except pale markings on posterior edge of pronotum and posterior edge of T1, rarely with more pale markings. [Body long and narrow; found only above 1 000 m.] P. aequatorialis -Eyes bare, but if with a few short hairs then body often with more yellow markings 14 14. Scrobal furrow (vertical groove on upper mesepisternum, as in Fig. 25) deep and complete, though sometimes shallower in lower part. T1 1.8 x as long as wide at posterior margin (Fig. 87). [With yellow on clypeus, propodeum, and posterior bands on T1-T2; usually with yellow also on scutellum and metanotum. Propodeum with erect hairs that are nearly as long as maximum width of propodeal orifice (Fig. 90).] P. occidentalis -Scrobal furrow usually shallow and incomplete (very faint in lower part). T1 at least 2 x as long as wide at posterior margin (Figs. 85-86), except in P. scrobalis which usually has fewer yellow markings than most P. occidentalis 15 15. Propodeum with erect hairs that are nearly as long as maximum width of propodeal orifice (as in Fig. 90).