Natural History Bulletin oJlbaraki University 3: 9-14,1999 The relative abundance of swarm-founding social wasps in the Congo Basin (Insecta: Hymenoptera; Vespidae, Polistinae) James M. Carpenter l and John W. WenzeF IDepartment ofEntomology, American Museum ofNatural Hist01y, Central Park West at 79 th Street, New York, NY 10024, Us. A. 2Department ofEntomology, The Ohio State University, Abstract The relative abundance of swann-founding species among social wasps in tropical Africa is assessed, based on field work in the Central African Republic. Two swann-founding species, belonging to the genus Polybioides, and II independent-founding species, belonging to the genera Polistes, Belonogaster and Ropalidia, were collected. The two swann-founding species represented less than 3% of nests, and 20% of all foragers. The preponderance of independent-founding species contrasts with relative proportions reported from the Neotropics, tropical Australia, and Southeast Asia. Key words Hymenoptera, Vespidae, Polistinae, social wasps, swann-founding, Congo Rainforest Introduction A basic biological distinction in social wasps is in colony foundation, which may be by one or a few foundresses or by swarms of workers accompanying queen(s) (swarm-founding). Jeanne (1991) called attention to the success of swarm- founding species relative to independent-founding species, as measured by four measures of prevalence including individual and colony abundance, range and species richness. He cited various studies establishing a much greater relative abundance of swarm-founding species in the Neotropics, e. g. up to 90% of individuals at a given locality, but then suggested that swarm- founding species were much less abundant in the Old WorId tropics. This suggestion was based on his own field work in northern Australia, and citation of Richards' (1978) field work there, as well as studies in India (Carl, 1934), the Indo-Malayan tropics (van der Vecht, 1962, 1966), and Madagascar (Vesey-Fitzgerald, 1950). However, Kojima (1993) questioned this conclusion, because his own collections in northern Australia showed 54% of colonies belonged to swarm- founding species of Ropalidia, as did the great majority of foragers. He noted that a minority of colonies he collected in the Philippines and Papua New Guinea were of swarm-founding species, but cited the data of Inoue et al. (1990) that showed a large majority of foragers in Sumatra were swarm-founding species. Kojima and van Achterberg (1997) also showed an overall majority of swarm-founding species, 63.4% if "probable swarm founders" were included, in Malaise trap samples taken over ten years on six Indo-Malayan islands. At the Mudumalai preserve in Tamil Nadu, India, swarming Ropalidia montana was by far the most common social wasp in August, 1990 (JWW, personal observation). Thus, swarm-founding species have been found to be generally more abundant than independent-founding species where this has been studied. In July, 1998, we participated in a survey of the Dzanga-Sangha Reserve in the Central African Republic, sponsored by the Center for Biodiversity and Conservation at the American Museum of Natural History. Located in the far southwestern corner of the country, between the borders with Cameroon and the Congo Republic, a protected area of more than 4000 km 2 includes two National Parks, Dzanga and Ndoki, and the Dzanga-Sangha Dense Forest Reserve. The national park is sheltered against human impacts, while the forest reserve allows hunting and rural development, especially around the towns of Bayanga and Lidjombo. Establishment of the reserve came about especially through the efforts of the World Wildlife Fund (WWF), and the survey was undertaken in collaboration with WWF. The forest is typical Congo Basin rainforest, and the reserve protects thousands of forest elephants and gorillas, but other aspects of the biota are less well studied. For our part of the survey, we concentrated on systematic collecting of social wasps. The Congo Basin is home to the two swarm-founding social wasps in Africa, both members of the genus Polybioides, as well as independent- founding species in the genera Polistes, Ropalidia and