Key to Solenopsis nigella species complex

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The following is based on: Pacheco, J.A. & Mackay, W.P. 2013. The systematics and biology of the New World thief ants of the genus Solenopsis (Hymenoptera: Formicidae). Edwin Mellen Press, Lewiston, New York. 501 pp. PDF

The nigella species complex is a group of New World thief ants in the genus Solenopsis.

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1

  • Concolorous dark brown; eye with 20-60 ommatidia; lateral clypeal teeth well developed, slightly extending past anterior clypeal border; lower mesopleuron and metapleuron horizontally striated; petiole and postpetiole lacking sculpturing . . . . . 2 (nigella subgroup)
  • Bicolored, reddish-brown body, darker brown gaster; eye with 17-50 ommatidia; lateral clypeal teeth well developed, considerably extending past anterior clypeal border (0.02-0.06 mm past border); nearly entire mesosoma horizontally striated (occasionally with small patch lacking sculpturing on pronotum, but if so, entire propodeum striated); usually entire petiole and postpetiole with punctate/roughened sculpturing (occasionally sculpturing restricted to basal portions of petiole and postpetiole) . . . . . 8 (metanotalis subgroup)

2

return to couplet #1

  • Eye kidney-shaped, 30-35 ommatidia, nearly reaching mandible insertion (see Solenopsis macrops); total length 1.4-1.5 mm; northern Argentina . . . . . 3
  • Eye oval, 20-60 ommatidia, distant from mandible insertion (see Solenopsis andina); total length 1.4-2.8 mm; Argentina and Brazil . . . . . 4

3

return to couplet #2

  • Petiole and postpetiole smooth and shiny, without sculpturing; eye larger, ~35 ommatidia, eye length ~0.16 mm, eye width ~0.70-0.80 mm; head slender in full face view (0.4-0.41 mm); Argentina (Buenos Aires) . . . . . Solenopsis macrops
Solenopsis macrops casent0103214 head 1.jpg
Solenopsis macrops casent0103214 profile 1.jpg
  • Petiole and postpetiole with punctate/roughened sculpturing; eye smaller; ~30 ommatidia, eye length ~0.12 mm, eye width ~0.06 mm; head wider (~0.46 mm); Argentina (Mendoza) . . . . . Solenopsis photophila
Solenopsis photophila casent0103211 head 1.jpg
Solenopsis photophila casent0103211 profile 1.jpg

4

return to couplet #2

  • Relatively larger, total length 2.4-2.8 mm; eye larger, 45-60 ommatidia . . . . . 5
  • Relatively smaller, total length 1.4-2.0 mm; eye smaller, 20-35 ommatidia . . . . . 6

5

return to couplet #4

  • Head larger, length 0.62-0.74 mm, width 0.64-0.71 mm; total length 2.6-2.8; sides of head nearly straight; eye with 45-55 ommatidia; striae restricted from mid to basal portion of mesopleuron; Argentina (Jujuy) . . . . . Solenopsis andina
Solenopsis andina casent0103212 head 1.jpg
Solenopsis andina casent0103212 profile 1.jpg
  • Head smaller, length ~0.66 mm, width ~0.6 mm; total length ~2.4 mm; sides of head noticeably convex; eye with 50-60 ommatidia; striae covering entire mesopleuron; Argentina (Neuquen) . . . . . Solenopsis schilleri
Solenopsis schilleri casent0103213 head 1.jpg
Solenopsis schilleri casent0103213 profile 1.jpg

6

return to couplet #4

  • Eye smaller, 20-25 ommatidia; total length 1.4-1.6 mm; scape length 0.28-0.36 mm; lacking vertical striae anterior to eye, between eye and clypeal border; Argentina and Brazil . . . . . Solenopsis gensterblumi
  • Eye larger, 25-35 ommatidia; total length 1.7-2.0 mm; scape length 0.38-0.44 mm; striae present between eye and clypeus . . . . . 7

7

return to couplet #6

  • Lacking vertical fine striae on frontal lobes (2 coarse striae may be present); lacking tooth at subpeduncular process (bump may be present); head thinner in frontal view (width 0.40-0.46 mm); Argentina (Catamarca) . . . . . Solenopsis oculata
Solenopsis oculata casent0103205 head 1.jpg
Solenopsis oculata casent0103205 profile 1.jpg
  • Fine vertical striae present on frontal lobes extending> 0.15 mm; well-developed tooth at subpeduncular process; head wider (width 0.64-0.70 mm), Argentina and Brazil . . . . . Solenopsis nigella
Solenopsis nigella casent0103217 head 1.jpg
Solenopsis nigella casent0103217 profile 1.jpg

8

return to [[#1 |couplet #1]

  • Moderately hairy, with erect and suberect hairs on all body surfaces, generally more than 10 on dorsum of mesosoma; lateral clypeal teeth extend slightly (0.02 mm) past anterior clypeal border; eye smaller, ~17 ommatidia; pronotum without sculpturing, lacking horizontal striae roughened/punctate sculpturing restricted basally on petiole and postpetiole; Argentina (Chaco, Tucuman) . . . . . Solenopsis shiptoni
Solenopsis shiptoni casent0103210 h 1 high.jpg
Solenopsis shiptoni casent0103210 p 1 high.jpg
  • Sparsely pilose, with scattered erect and suberect on body surfaces, generally fewer than 10 on the dorsum of mesosoma; lateral clypeal teeth extend considerably past (0.05 mm) anterior clypeal border; eye larger, 40-50 ommatidia; entire mesosoma horizontally striated, including pronotum (dorsum of mesosoma partially smooth); entire petiole and postpetiole except for dorsum covered with roughened/punctate sculpturing . . . . . 9

9

return to [[#8 |couplet #8]

  • Vertical striae present, between eye and clypeal margin; total length 2.1-2.3 mm; Argentina and Uruguay . . . . . Solenopsis metanotalis
Solenopsis metanotalis arga casent0103208 head 1.jpg
Solenopsis metanotalis arga casent0103208 profile 1.jpg
  • Lacking striae between eye and clypeal margin; total length 1.9-2.2 mm; Argentina, southern Brazil and Uruguay . . . . . Solenopsis emiliae
Solenopsis metanotalis emiliae casent0103200 head 1.jpg
Solenopsis metanotalis emiliae casent0103200 profile 1.jpg