In South America, Solenopsis saevissima and S. invicta are the most common fire ants. Nests are founded in areas under anthropic interference like urban or rural areas, but S. invicta is found preferentially in those with the greatest anthropic interference. However, we do not know the rates at which they exist in anthropized areas next to high density of native vegetation. Areas with 60 to 90% of native Atlantic Forest were selected to verify the occurrence of both species in rural and urban areas. We investigated the molecular diversity and applied the reconstruction of the ancestral state analysis for each species. A total of 186 nests were analyzed and we found that the two species had the same proportion in the urban area. However, S. saevissima had a higher rate of prevalence in the rural area, in addition to having a greater number of haplotypes and ancestry associated with this type of habitat for the region. S. invicta had the same number of haplotypes in both rural and urban regions, and less haplotypic diversity. We conclude that S. saevissima is a species typically associated with rural areas and S. invicta, although present, is not dominant in urban areas.

The present investigation deals with some aspects of the diversity of fire ants (Hymenoptera: Formicidae) in their native range. The Red Imported Fire Ant Solenopsis invicta is native to the tropical and subtropical inland territories of South America. In Brazil, it mainly occurs around the Pantanal region and across the Paraguay river, a region composed of grasslands which are seasonally flooded. Recent studies have evidenced this fire ant species is gradually spreading to other regions of Brazil. In the present investigation, we surveyed the molecular diversity of S. invicta populations across fragments of Atlantic Forest in São Paulo, Brazil, using mtDNA COI haplotypes. Fire ant nests were sampled along the highways lining the northern and southern slope sides of the mountain range Serra do Mar, SP, Brazil. Four haplotypes were identified (H1–H4), which were assessed for similarity to deposited records by other authors, revealing that the haplotypes H1 and H2 are likely of foreign origin through recent reintroduction via a marine port to the south of the Serra do Mar mountain range. On the other hand, the haplotypes H3 and H4, predominating among the inland samples from the northern side of the mountain range, were most similar to previous records from more central regions of Brazil. Haplotypes clustered into distinct supergroups, further pointing to the occurrence of two separate expansion waves of S. invicta in the region. We suggest the obtained pattern indicates the mountain range may function as a geographical barrier deferring gene flow.

Discothyrea is a genus composed of specialist predatory species rarely recorded and with little known biology. Specimen collection is usually associated with preserved native vegetation. In this work, we explore the landscape of sites with occurrence of Discothyrea seeking to improve knowledge about the natural history of this genus. Species of Discothyrea were recorded in ten Atlantic Forest sites. We analyzed the landscape around the place of occurrence of each species using a 500-m buffer. We classified the landscape as heterogeneous and homogeneous according to the percentage of natural (native vegetation), urban, and rural areas. We found 67 specimens of Discothyrea; 59 of them were D. sexarticulata, occurring in 88% of the fragments. There were also eight specimens of D. neotropica occurring in 12% of the fragments. The results show that D. sexarticulata can be found in homogeneous landscapes with anthropic influence (0-51% of rural area and 0-68% of urban area). Discothyrea neotropica is found in heterogeneous landscapes with a dominant presence of native vegetation (between 74-95%). The results improve knowledge on the biology of Discothyrea mainly in relation to the vicinity of occurrence sites. In addition, the results indicate that regional studies are important to understand species ecology.