Wolbachia infections in native and introduced populations of fire ants (Solenopsis spp.)

Wolbachia are cytoplasmically inherited bacteria that induce a variety of e ffects with fitness consequences on host arthropods, including cytoplasmic incompatibility, parthenogenesis, male-killing and feminization. We report here the presence of Wolbachia in native South American populations of the fire ant Solenopsis invicta, but the apparent absence of the bacteria in in troduced populations of this pest species in the USA. The Wolbachia strains in native S. invicta are of two divergent types (A and B), and the frequen cy of infection varies dramatically between geographical regions and social forms of this host. Survey data reveal that Wolbachia also are found in ot her native fire ant species within the Solenopsis saevissima species comple x from South America, including S. richteri. This latter species also has b een introduced in the USA, where it lacks Wolbachia, Sequence data reveal c omplete phylogenetic concordance between mtDNA haplotype in S. invicta and Wolbachia infection type (A or B). In addition, the mtDNA and associated gr oup A Wolbachia strain in S. invicta are more closely related to the mtDNA and Wolbachia strain found in S. richteri than they are to the mtDNA and as sociated group B Wolbachia in S. invicta. These data are consistent with hi storical introgression of S. richteri cytoplasmic elements into S, invicta populations, resulting in enhanced infection and mtDNA polymorphisms in S. invicta. Wolbachia may have significant fitness effects on these hosts (eit her directly or by cytoplasmic incompatibility) and therefore these microbe s potentially could be used in biological control programmes to suppress in troduced fire ant populations.