Population genetics and history of the introduced fire ant, Solenopsis invicta Buren (Hymenoptera : Formicidae), in Australia

The red imported fire ant, Solenopsis invicta, a damaging invasive pest, was discovered in February 2001 in Brisbane, Australia at two sites, Fisherman Islands and suburban Richlands-Wacol. Using four microsatellite loci and the protein marker Gp-9, we compared the two infestations with each other, and with potential source populations in North and South America to better understand the history of their introduction to Brisbane. Based on an analysis of molecular variance, as well as a maximum likelihood tree of colonies from the two Australian sites, we found that the two sites were genetically distinct and were almost certainly introduced separately. All of the colonies at Fisherman Islands were monogynous, headed by a single queen, while the Richlands-Wacol site had a mixture of single-queen monogynous and multiple-queen polygynous colonies. However, the monogynous and polygynous colonies at the Richlands-Wacol site were not genetically distinct from each other, and probably constitute a single, mixed introduction. Based on allele frequencies at the microsatellite loci, and Gp-9, both Australian infestations were more similar to North American populations than to South American, though the Fisherman Islands infestation was intermediate, making it difficult to assign. Thus, there has been one introduction from either a North or South American monogynous population at Fisherman Islands, and one introduction from a mixed monogynous/polygynous North American population at Richlands-Wacol. These findings have implications for the control of the current infestations, as well as for the quarantine regulations necessary to prevent additional introductions to Australia.