Key to Recurvidris of Thailand
Until now, eleven species of the genus Recurvidris have been known from Asia (Table 1). Among them, three species are found in Thailand and they belong to two species groups (sensu Bolton, 1992): Recurvidris kemneri group (R. chanapaithooni) and R. recurvispinosa group (R. browni and R. recurvispinosa).
Mandibular dentition, the presence of hairs on propodeal dorsum and the presence of infradental lamellae or ridges that link the propodeal spines to the metapleural lobes were characters used by Bolton (1992) to distinguish the two species groups mentioned above. These morphological characters were confirmed and used by several authors who described new species of the genus after Bolton (1992) (Xu and Zheng, 1995; Zhou, 2000; Zettel, 2008). The present paper also follows the previous works. In the specimens used in the present paper, the number and shape of teeth on the mandible of the worker (4-5 on masticatory margin and 0-1 on basal margin) are constant within each species even in older specimens (aged individuals). We strongly recommend that whenever preparing dry specimens of the genus, the mandibles of several specimens from each colony must be opened. The peculiar shape of propodeal spine is an important character (curving upwards and forwards from its base) to separate the genus from the others and it seems to be constant in shape and length within each species. However, for Thai Recurvidris the shape, curve, and length of propodeal spine are not very useful to distinguish among the three species. The sculpturing, colour, and pilosity on the body are more important for species identification. The genus is clearly monomorphic in worker caste (at least in Thai species) with a small size variation occurring within species. Thus, body size can be separated into large and small species. In this paper body size has been used, separating R. browni from R. recurvidris (couplet 2) and R. chanapaithooni from R. nigrans.
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- Head entirely smooth and shiny; basal margin of mandible with a small tooth which is widely separated from basal (fourth) tooth; basal tooth acute apically; propodeal declivity lacking infradental lamella or ridge linking propodeal spine to metapleural lobe; dorsum of propodeum with 2 pairs of standing hairs . . . . . Recurvidris chanapaithooni
- Head largely sculptured (reticulate, reticulate-punctate to reticulate-granular); basal margin of mandible unarmed; basal (fourth or fifth) mandibular tooth blunt or bidenticulate apically; propodeal declivity with narrow infradental lamella or ridge linking propodeal spine to metapleural lobe; dorsum of propodeum without standing hairs . . . . . 2
return to couplet #1
- Masticatory margin of mandible with four teeth, basal tooth bidenticulate; much smaller species (HW 0.36-0.41 mm); head in full-face view narrow, rectangular and slightly longer than broad . . . . . Recurvidris recurvispinosa
- Masticatory margin of mandible with five teeth, basal tooth blunt or truncate at apex; larger species (HW 0.53-0.56 mm); head in full-face view round and almost as long as broad . . . . . Recurvidris browni