DURATION OF PROTOPOLYBIA-EXIGUA-EXIGUA (DE-SAUSSURE) NESTS AND RELATED ASPECTS AS INFLUENCED BY PHORID FLY INFESTATION (VESPIDAE, POLISTINAE, EPIPONINI)

The main characteristics of 55 nests of Protopolybia exigua exigua wer e periodically evaluated in Ribeirao Preto, southeastern Brazil. Altho ugh the queens' life-span can eventually reach one year, nests barely thrive for six months because most of them are periodically invaded by the scavenger phorid fly, Megaselia aff. picta. Under heavy infestati on the adult wasp population partially closes the nest entrance, migra tes and constructs a new nest in the neighborhood. Afterwards the old- nest's entrance can be completely closed by the wasps which results in blocking the parasitoid flies inside. In the tropics, predation by an ts is considered the main selective pressure which shaped most of the bionomic characteristics of Polistinae wasps, It is suggested that Meg aselia can easily overcome the usual wasps defensive tactics just beca use they are so specialized against ants. Aerial raids, fast erratic-j erking movements, rapid and efficient oviposition behavior, etc. can e ventually turn Megaselia into a very important enemy of some social wa sps.