Key to Crematogaster borneensis group queens

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This key is based on: Feldhaar, H., Maschwitz, U., Fiala, B. 2016. Taxonomic revision of the obligate plant-ants of the genus Crematogaster Lund (Hymenoptera: Formicidae: Myrmicinae), associated with Macaranga Thouars (Euphorbiaceae) on Borneo and the Malay Peninsula. Sociobiology. 63: 651-681.

Species identification of Macaranga-associated Crematogaster (Crematogaster borneensis-group) is easier and more conclusive based on queens as they possess more distinct characters than workers (i.e. length of compound eyes and the ocelli).

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1

Feldhaar et al. 2016. Figure 3.
  • Queens light to medium-brown; compound eyes oval and > 0.5 mm diameter (longest distance) when head is in lateral view (e.g. Fig S1.1A and S1.1B). . . . . . 2
  • Queens medium- to dark brown (nearly black); compound eyes round to slightly oval and < 0.5 mm in diameter (longest distance) when head is in lateral view (e.g. Fig S1.3A and S1.3B). . . . . . 4

2

return to couplet #1

  • Distance between lateral ocelli always greater than diameter of anterior ocellus (OD1 > OW) (Fig 3.1; Fig S1.1A and S1.1B). Head (in full-face view) always longer (measured from anterior clypeal margin to posterior margin of head) than wide (measured at the widest point; head capsule only, compound eyes not included) (CI < 0.95). . . . . . Crematogaster borneensis
  • Anterior ocellus as wide as or wider in diameter than distance between lateral ocelli (Fig 3.2 and 3.3), or, if the anterior ocellus is not as wide as the distance between the two lateral ocelli, then CI > 0.95. . . . . . 3

3

return to couplet #2

  • Length of scape > 0.75 mm. Diameter of compound eyes (EL) rarely < 0.65 mm (Fig 3.2). LHT rarely <1.1 mm. Species colonizes predominantly waxy hosts of the section Pruinosae (M. hosei, M. pearsonii, M. pruinosa) (Fig S1.2A and S1.2B). . . . . . Crematogaster linsenmairi
  • Length of scape usually <0.75 mm. Diameter of compound eyes (EL) between 0.55 and 0.65 mm, usually around 0.6 mm (Fig 3.3). LHT rarely > 1.1 mm (specimens with LHT between 1.1 and 1.8 were rarely found in Sarawak only). Widespread on non-waxy host species of the section Pachystemon (M. bancana, M. indistincta, M. angulata, M. trachyphylla, M. petanostyla, M. hullettii, M. calcicola, M. kingii) (Fig S1.4A and S1.4B). . . . . . Crematogaster captiosa

4

return to couplet #1

  • Small queens with elongated head (CI < 0.9) and small compound eyes (EL 0.3 – 0.32; Legs in comparison to alitrunk length relatively short (REL < 0.28), HW 0.95 to 1.02 (Fig 3.8; Fig S1.8A and S1.8B). Postpetiole always wider than petiole (or at most as wide) (PI ≤ 1.0). Species endemic to east of Peninsula Malaysia and colonizing waxy hosts of the section Pachystemon (M. constricta and M. hypoleuca). . . . . . Crematogaster roslihashimi
  • Head of queens less elongated (CI > 0.9) and small to medium sized compound eyes (EL between 0.34 and 0.5 mm). . . . . . 5

5

return to couplet #4

  • Scape length (SL) > 0.7 mm. Postpetiole always wider than petiole (PI < 1.0). HL between 1.21 and 1.42, head usually as wide as or wider than long (Fig 3.6; Fig S1.5A and S1.5B), rarely longer than wide (CI usually > 1.0). Widespread species, occurring over the whole geographical range of the symbiosis that colonizes waxy hosts of the section Pachystemon (M. beccariana, M. havilandii, M. hypoleuca). . . . . . Crematogaster decamera
  • Scape length (SL) < 0.7 mm. Petiole usually as wide as or wider than postpetiole (PI > 1.0). . . . . . 6

6

return to couplet #5

  • Eye length (EL) between 0.34 to 0.38 mm. HL < 1.22, HW 1.01 – 1.2 mm. Compound eyes relatively small in relation to head length in lateral view (REL 0.28 – 0.34; Fig 3.7; Fig S1.6A and S1.6B). The first three segments (distal) of the flagellum of the antenna form a distinct club. Species found on Borneo (Sabah, Sarawak, East Kalimantan), mostly on waxy host plants of the section Pachystemon (M. havilandii, M. hypoleuca, M. motleyana) and rarely on the non-waxy M. angulata and M. indistincta (in primary forest or at higher elevation). . . . . . Crematogaster maryatii
  • Eye length (EL) between 0.39 and 0.5 mm, HL >0.18. Flagellum not with distinct club (may look slightly like 3- or 4-segmented club) . . . . . 7

7

return to couplet #6

  • Compound eyes relatively large (EL 0.45 to 0.5 mm). Head as wide as or wider than long (CI > 1.0) and petiole usually wider than postpetiole in dorsal view (PI > 1.0). ROD between 0.13 and 0.17 (Fig 3.4; Fig S1.7A and S1.7B). Species endemic to Borneo, mainly found in Sabah, occurring mostly on non-waxy host plants of the section Pachystemon (e.g., M. angulata, M. indistincta) and on the slightly wax covered M. glandibracteolata . . . . . Crematogaster claudiae
  • Compound eyes rarely larger than 0.45 mm (EL 0.39 – 0.47 mm). Cephalic index (CI) between 0.96 and 1.07. Postpetiole usually as wide as or wider than petiole in dorsal view (PI < 1.0). ROD between 0.09 and 0.13 (Fig 3.5; Fig S1.3A and S1.3B). Petiole flat and rounded when in dorsal view. Species colonizes non-waxy hosts of the section Pachystemon (M. bancana, M. hullettii, M. kingii, M. trachyphylla, M. umbrosa); on Peninsula Malaysia found at higher elevation only (approximately > 500m ); not found in Sabah. . . . . . Crematogaster hullettii