The solitary wasp genus Orancistrocerus from Vietnam, with descriptions of two new species (Hymenoptera, Vespidae, Eumeninae) Author Nguyen, Lien Thi Phuong https://orcid.org/0000-0003-3527-9577 Insect Ecology Department, Institute of Ecology & Biological Resources (IEBR), Vietnam Academy of Science & Technology, 18 Hoang Quoc Viet Road, Nghia Do, Cau Giay, Hanoi, Vietnam & Graduate University of Science and Technology, Vietnam Academy of Science & Technology, 18 Hoang Quoc Viet Road, Nghia Do, Cau Giay, Hanoi, Vietnam phuonglientit@gmail.com Author Nguyen, Anh D. https://orcid.org/0000-0001-9273-0040 Insect Ecology Department, Institute of Ecology & Biological Resources (IEBR), Vietnam Academy of Science & Technology, 18 Hoang Quoc Viet Road, Nghia Do, Cau Giay, Hanoi, Vietnam & Graduate University of Science and Technology, Vietnam Academy of Science & Technology, 18 Hoang Quoc Viet Road, Nghia Do, Cau Giay, Hanoi, Vietnam Author Dang, Hoa T. https://orcid.org/0000-0002-8312-2825 Insect Ecology Department, Institute of Ecology & Biological Resources (IEBR), Vietnam Academy of Science & Technology, 18 Hoang Quoc Viet Road, Nghia Do, Cau Giay, Hanoi, Vietnam & Graduate University of Science and Technology, Vietnam Academy of Science & Technology, 18 Hoang Quoc Viet Road, Nghia Do, Cau Giay, Hanoi, Vietnam text ZooKeys 2024 2024-03-01 1193 95 110 http://dx.doi.org/10.3897/zookeys.1193.116087 journal article http://dx.doi.org/10.3897/zookeys.1193.116087 1313-2970-1193-95 1457DD9918B0413CA0D0FBD11878A45F EA19A2400D965CA3AB43B8CCC821462A Genus Orancistrocerus van der Vecht, 1963 Orancistrocerus van der Vecht, 1963: 58, 99. Type species: Odynerus drewseni de Saussure, 1857, by original designation. Diagnosis. Anterior surface of pronotum without pits or foveae. Tegula not evenly rounded posteriorly, emarginate adjoining parategula and often shorter than the latter. Axillary fossa in dorsal view much narrower than long, slit-like. Propodeum without deep fossae, submarginal carina and valvula not protruding; propodeal dorsum not forming raised shelf-like area behind metanotum. Metasomal terga with short apical lamellae; TI transversely carinate, without broad longitudinal median furrow posterior to carina, long, dorsal surface ~2 x or less as wide as long. Male antenna hooked apically. Generic relationships. Orancistrocerus is a small genus, currently with five species and with four valid subspecies in O. aterrimus , which is widely distributed from India to China, including Laos and Vietnam. The second most widely distributed species, O. drewseni , with three subspecies, is distributed in several tropical climatic zones of China (including Taiwan), Japan, and Laos, while the two subspecies of O. bicoloripennis is distributed only in Malaysia and Indonesia. Orancistrocerus moelleri , with two subspecies, is recorded from South China, northern India adjacent to South China, and Myanmar ( van der Vecht 1963 ; Giordani Soika 1973 ; Tan et al. 2018 ). The remaining species, O. altus , O. thanghen sp. nov., and O. thanhnhat sp. nov., are known only from northern Vietnam, but it is assumed that these also occur in southern China as the type localities border that region. More interestingly, all three Vietnamese species have been found only in limestone areas. Van der Vecht (1963) established the genus Orancistrocerus but did not discuss any similarities or relationships between Orancistrocerus and other eumenine genera. Recently, a phylogenetic tree showing relationships within the subfamily Eumeninae was provided based on molecular data ( Luo et al. 2022 ), and in that study, Orancistrocerus is closely related to Euodynerus . Morphological similarities of these two genera are as follows: metasoma not petiolate; fore wing with second submarginal cell not petiolate; propodeum without deep fossae; metanotum without tubercles; anterior surface of pronotum without pits or foveae. TI transversely carinate is a character to separate Orancistrocerus from Euodynerus (TI not carinate in Euodynerus ). In the phylogenetic tree by Luo et al. (2022) , Orancistrocerus and Pararrhynchium are not closely related, but they are very similar to each other in morphology, owing to the metasoma not petiolate, forewing with second submarginal cell not petiolate, metanotum without tubercles, anterior face of pronotum without pits or foveae, propodeum with submarginal carina and valvula not produced, TI transversely carinate, axillary fossa narrower than long, slit-like, tegula not exceeding parategula, and male antenna hooked apically. Orancistrocerus differs from Pararrhynchium in having the propodeal dorsum not forming a shelf-like area behind the metanotum and the metasomal terga with short apical borders (propodeal dorsum usually forming a shelf-like area behind the metanotum more than one ocellar diameter long; metasomal terga usually with some well-developed apical lamellae in Pararrhynchium ). The genus Malayepipona was not included by Luo et al. (2022) , but, based on a study of the Vietnamese material, Orancistrocerus is morphologically also similar to Malayepipona in the shape of the mesosoma, propodeum, and metasoma in dorsal view, in having the first metasomal tergum angular in profile, and TI with the anterior portion separated from the horizontal part by a more or less distinct transverse ridge. These two genera can be distinguished in having the tegula not exceeding the parategula, axillary fossa in dorsal view much narrower than long, slit-like in Orancistrocerus (tegula at least equaling parategula posteriorly; axillary fossa in dorsal view not slit-like, oval in Malayepipona ). Origin of genus. Even if there is no existing hypothesis on biogeographic history of Orancistrocerus , our working hypothesis is that these species may have originated in the Himalayas running between China and India, perhaps during episodes of orogeny, then dispersed into South China and northern India as well as Southeast Asia, including Vietnam, Myanmar, Malaysia, and Indonesia. Naturally, a comprehensive revision and phylogenetic analysis are needed to test this hypothesis and establish a robust estimate for the complex biogeographic history of Orancistrocerus and other Asiatic Eumeninae .