First Observation of Polygyny in Fire Ants, Solenopsis SPP., in South America

Polygyny, the coexistence of two or more egg-laying queens in a single colony of a social insect, occurs in several subfamilies of ants (Wilson 1971). The species of Solenopsis, however, were considered to be monogynous until Banks et al. (1973), and Glancey et al. (1973) observed polygyny in Solenopsis geminata (F.) and Solenopsis invicta Buren, respectively. Subsequently, Summerlin (1976) found a single polygynous colony of Solenopsis xyloni McCook. The existence of a spectrum from monogyny to extreme polygyny in the North American S. invicta population was substantiated by Fletcher et al. (1980). Populations of polygynous S. invicta are now known from Florida, Georgia, Mississippi, Louisiana, Texas (Lofgren and Williams 1984), Alabama, Arkansas, and Oklahoma (Banks and Wojcik unpublished). These populations are spreading, and in some cases are proving to be more difficult to control with pesticides than monogynous populations (Glancey et al. 1987). They are also characterized by increased densities of both ants and mounds (Lofgren and Williams 1984). Thus, polygyny in fire ants is currently a subject of interest and concern. We have not encountered polygynous colonies in our extensive surveys for biological control agents for fire ants in the states of Mato Grosso and Mato Grosso do Sul, Brazil, the presumed homeland of S. invicta (Wojcik 1986). Recently, however, we extended our surveys to Argentina, where we collected colonies of polygynous Solenopsis richteri Forel and Solenopsis quinquecuspis Forel. We were alerted to the possibility that we had encountered polygynous fire ants by the enormous biomass of brood in a colony of S. richteri, which has been separated from the soil by flotation (Banks et al. I98 1). This colony yielded 16 non-physogastric, dealate