.. Journal of Insect Behavior. Vol. 4. No. J. 1991 '1 Short Communication Interspecific Occupation of a Tropical Social Wasp Colony (Hymenoptera: Vespidae: Polistes) Sean O'Donnell I and Robert L. Jeanne 1 Accepted December 27. 1990; reI'ised Jal/uary 25, /991 KEY WORDS: Costa Rica; dominance interactions; nest architecture; ca//udcns;s; Po/- iSles illstabilis; social parasitism; usurpation. Social parasitism, involving the takeover of a queenright nest by a foreign reproductive female, has been documented in all families of social Hymenop- tera (Wilson, 1971). Taylor (1939) hypothesized that the evolution of social parasitism has passed through three main steps or grades: usurpation of con- specifics. facultative parasitism of related species. and finally, obligatory par- asitism (inquilinism). All three stages have been documented in the Vespinae (Matsuura and Yamane, 1990). Intraspecific and obligate interspecific social parasitism are well known in temperate-zone Polistinae (Klahn, 1988; Turil- lazzi et al .• 1990), but facultative interspecific parasitism has not been docu- mented in this subfamily (Wcislo, 1987). Snelling (1952) noted a Polistes nest with two females of different species (P. fuscatus and P. apaclllls) but gave no information on their reproductive status or behavioral intemctions. Here we present the first evidence of interspecific nest usurpation by a tropical pol- istine wasp, and the first interspecific polistine colony that did not include an obligate nest parasite. The Polistes colony we observed was attached to the ceiling of a porch at Hacienda la Pacifica near Canas, Guanacaste Province, Costa Rica. We observed the colony ad libitum from 28 June to 9 August 1989, when it was collected. Behavioral data were taken on 22 occasions (separated by at least 3 h) at various times of day between 0540 and 2100, for a total of 2.8 h. The size and brood content of the nest were recorded on 28 June, 25 July, and 9 August. On 25 July (0600) we marked all adult wasps on the nest for individual rec- ognition. I Department of Entomology. University of Wisconsin. Madison. Wisconsin 53706. 397 ) IINl I'h,'uultl Puhh ...hml-! (\I'llt1r:llillr\