Geographical transition zone of Solenopsis fire ants (Hymenoptera: Formicidae) and Pseudacteon fly parasitoids (Diptera: Phoridae) in the state of S？o Paulo, Brazil

solenopsis saevissima (smith) and solenopsis invicta buren are the most abundant and widely distributed fire ants in brazil. the occurrence of the two fire ant species and of their parasitoids pseudacteon spp. is described for a climatic and phytophysiognomic transition area in the state of s？o paulo. both fire ant species have a parapatric distribution, apparently determined by the climate: s. saevissima predominates in the north part of s？o paulo (aw climate), while s. invicta in the south (cfa climate). a sympatric area is observed between the latitudes 21os and 23os. two different communities of parasitic decapitating flies were associated with s. saevissima in the north and with s. invicta in the south, with a sympatric area in the municipality of s？o carlos (21o58's 47o53'w). the possible causes of this biogeographic pattern are discussed. preference tests with pseudacteon flies challenge the association of p. litoralis borgmeier, p. curvatus borgmeier, p. wasmanni schmitz, p. pradei borgmeier and p. obtusus borgmeier with s. saevissima, and p. dentiger borgmeier, p. disneyi pesquero and p. lenkoi borgmeier & prado with s. invicta.