GEOGRAPHIC RANGES AND PATTERNS OF DIVERSITY FOR PSEUDACTEON FLIES, PARASITOIDS OF SOLENOPSIS ANTS, FROM ARGENTINA AND BRAZIL

¹Centro de Estudios e Investigaciones, Universidad Nacional de Quilmes, Roque Saenz PeŇa 180, 1876 Bernal, Bs As, Argentina, E-mail: pfolgarait@unq.edu.ar
²USDA-ARS, CMAVE, Gainsville, FL 32604, USA
³Department of Zoology, University of Texas, Austin, TX 78712, USA.

More than 40 species have been described within the cosmopolitan genus Pseudacteon, which specializes in attacking Solenopsis ants and is being considered to be used as a biological control tool in USA. Information on Pseudacteon records and distribution is currently dispersed and hardly published. However, this type of data is very important as a source of information on phorids localities for future captures and to infer phorids climatic tolerances to rear and release them at proper places in the States. Using bibliographic information, data from brazilian museums, and collections made by the authors, we compiled a data base on Pseudacteon throughout the distribution range of the two exotic fire ant pests, Solenopsis invicta (red) and Solenopsis richteri (black). The whole area included the region between 10-40†S and 35-65†W encompassing Argentina and Brazil. We used the grid method to estimate richness per cell and per phytogeographical regions and calculated equiprobabilistic curves following Rapoport (1982). We also estimated geographical ranges and climatic correlates for each species and classify them as broadly or narrowly distributed species.

Equiprobabilistic curves were calculated for each cell using as central points of observations four cells that span a latitudinal gradient. These cells were: Goiania-Brasilia (GB), Belo Horizonte-Sao Paulo (BHSP), Corrientes (CO), and Capital-Buenos Aires (CBA); the first two in Brazil and the latter two in Argentina. There was no clear latitudinal pattern in species richness but phytogeographical regions in Brazil had greater diversity. However, the pattern of species that were lost from the centers of observations towards other cells changed consistently if the center was calculated at lower latitudes or at higher ones. This means that most of the species found at CO and CBA represented assemblages of species found in GB and BHSP, and represented species with broad geographic ranges and climatic tolerances. These data suggest that the introduction of broadly distributed Pseudacteon species will be more successful because these species have been able to spread across different climatic and phytogeographical regions and may have greater physiological tolerances to abiotic variables. In fact, broadly distributed Pseudacteon flies represent species that currently find red and black fire ants throughout their geographic range of distribution.

Index terms: biogeography, biological control, fire ants, phorids, richness.