A revision of the Carebara pygmaea (Emery, 1887) species group (Hymenoptera: Formicidae) in Thailand Author Wimolsuthikul, Chaipat 0009-0001-7229-4752 Office of Natural Science Research, National Science Museum, 39, Moo zygosoma@gmail.com Author Yamane, Seiki 0000-0002-6865-0865 Haruyama-chô 1054 - 1, Kagoshima-shi, 899 - 2704 Japan. mayiopa0@gmail.com Author Samung, Yudthana 0000-0003-4069-4257 Khlong & Department of Medical Entomology, Faculty of Tropical Medicine, Mahidol University, Bangkok 10400, Thailand. yudthana.sam@mahidol.ac.th Author Jaitrong, Weeyawat 0000-0003-1362-0754 Office of Natural Science Research, National Science Museum, 39, Moo & Office of Natural Science Research, National Science Museum, 39, Moo & Khlong Luang, Pathum Thani, 12120 Thailand. polyrhachis@yahoo.com text Zootaxa 2024 2024-07-15 5481 1 79 100 http://dx.doi.org/10.11646/zootaxa.5481.1.5 journal article 299942 10.11646/zootaxa.5481.1.5 0423a610-a41f-4de4-9d39-289e7ec7168f 1175-5326 12742641 987E3EFF-7867-4186-A26A-79359DF762C8 Carebara pygmaea species group Diagnosis. Dimorphic. Major. Frons with longitudinal striation; posterior portion of head in full-face view usually with transverse striation (except for C. bokorensis lacking this striation); vertex without a pair of horns; frontal carinae with three pairs of erect hairs; mandible short, subtriangular, masticatory margin with five teeth (including large apical tooth); promesonotum in profile view distinctly convex to form a dome; promesonotal suture indistinct; metanotal groove present; propodeum distinctly lower than promesonotum; propodeal spine short, usually shorter than width at base; petiole in profile, with long anterior peduncle; postpetiole clearly shorter than petiole; gastral tergite I clearly larger than remaining segments combined. Minor. Head small, smooth and shiny; mandible relatively short, subtriangular, masticatory margin with five teeth (including large apical tooth); eye very small, present as a dot; promesonotum in profile view convex, smooth and shiny; promesonotal suture absent; metanotal groove distinct; propodeal spine absent; petiole with long anterior peduncle; postpetiole clearly shorter than petiole; gastral tergite I clearly larger than remaining segments combined. Ergatoid queen. Morphological character is similar to major worker in having large head but mesosoma is slightly larger than in major worker and ocelli are present. We placed C. bokorensis under the C. pygmaea species group because almost all characters of the minor and the major workers agreed well with the characteristics of the species group. The body sculptures and the condition of the hairs can be used to distinguish the species within the species group. We have tried to extract DNA using dry specimens but were unsuccessful using the PCR process. In future work, DNA barcoding should help to distinguish members of the C. pygmaea species group when obtaining fresh specimens. Currently, valid names included in the species group of Thailand . Carebara adisaki sp. nov. ; C. parva sp. nov. ; C. panhai Jaitrong, Pitaktunsakul & Jantarit, 2021 ; C. bokorensis Matsuura & Hosoishi, 2024 ; C. pygmaea ( Emery, 1887 ) ; C. rubra (Smith, 1860) , and C. transversalis (Smith, 1860) . Distribution. Sri Lanka , Laos , Cambodia , Thailand , Malaysia (Borneo), Indonesia ( Ternate to Sumatra ), and Philippines . Key to Thai species of Carebara pygmaea species group based on major worker 1 In dorsal view, posterior half of head and entire gastral tergite I without both erect and decumbent hairs ( Fig. 10A ).................................................................................................... C . pygmaea - In dorsal view, posterior half of head and entire gastral tergite I with dense or sparse erect or decumbent hairs ( Figs. 1A , 3A , 6A , 8A )............................................................................................. 2 2 Posterior one-third of head in full-face view with dense foveae, without transverse striation ( Fig. 1B ); gastral tergite I punctate ( Fig. 3C ).................................................................................. C. bokorensis - Posterior one-third of head in full-face view with transverse striation ( Figs 4B , 6B , 8B ); gastral tergite I smooth and shiny, at most weakly shagreened ( Figs. 1C , 6C , 8C )................................................................. 3 3 Mesosomal dorsum with erect hairs ( Fig. 6A )........................................................ C. panhai - Mesosomal dorsum without erect hairs ( Figs. 1A , 8A )........................................................ 4 4 Propodeal spines shorter than diameter of propodeal spiracle; first gastral tergite with erect hairs only along its posterior margin ( Fig. 1A ).............................................................................. C. adisaki sp. nov. - Propodeal spine almost as long as or slightly longer than diameter of propodeal spiracle; entire first gastral tergite covered with erect hairs ( Fig. 8A )...................................................................... C. parva sp. nov. Key to Thai species of Carebara pygmaea species group based on minor worker 1 Propodeal dorsum entirely punctate ( Fig. 5A, C )................................................... C. bokorensis - Propodeal dorsum smooth and shiny ( Figs. 2A , 7A , 9A , 11A ).................................................. 2 2 Antennal scape not reaching posterior margin of head ( Fig. 11B ); hairs on pronotum shorter than diameter of eye ( Fig. 11A )........................................................................................... C. pygmaea - Antennal scape reaching or extending beyond posterior margin of head ( Figs. 2B , 7B , 9B ); hairs on pronotum longer than diameter of eye....................................................................................... 3 3 Propodeal junction roundly convex ( Fig. 7A ); antennal scape extending beyond posterior margin of head ( Fig. 7B ); dorsa of petiole and postpetiole each with 2–4 erect hairs ( Fig. 7A ).............................................. C. panhai - Propodeal junction bluntly angulated ( Figs. 2A , 9A ); antennal scape reaching posterior margin of head ( Figs. 2B , 9B ); dorsa of petiole and postpetiole without erect hairs ( Figs. 2A , 9A )...................................................... 4 4 Peduncle of petiole punctate; PI1 240–275; larger species (HW 0.43–0.46 mm in minor worker; 1.02–1.06 mm in major worker)............................................................................... C . adisaki sp. nov. - Peduncle of petiole smooth and shiny; PI1 160–200; smaller species (HW 0.36–0.40 mm in minor worker; 0.79–0.83 mm in major worker)........................................................................... C . parva sp. nov.