Spread and social structure of the little fire ant (Wasmannia auropunctata) in Florida

Social structures of invasive ants are often associated with supercoloniality, i.e., a social structure that encompasses many colonies on a large geographic scale with lack of boundaries and aggression between them. However, determining supercoloniality is challenging and requires several complementing methods. Acceptance tests are often used to indicate social structure membership; acceptance may indicate affinity, while lack of acceptance (e.g., aggressive behavior), may be explained by underlying genetic differences or environment-related factors. Therefore, complementing behavior, genetics and environmental assessments are advantageous to decipher social structures of invasive ants, especially as their social structures probably aid in their spread. We characterized the social structure of Wasmannia auropunctata (little fire ant, e.g., LFA) in Florida using behavioral and genetic assessments, and mapped the recent spread of this species, a widespread environmental and agricultural pest. We documented a significant northern expansion from previous reports. We conducted behavioral assays to detect acceptance/non-acceptance by introducing dyads from different populations in Florida, and of nestmates as control. We found at least five distinct subpopulations that demonstrated acceptance within, and non-acceptance between them. The farthest acceptance within a subpopulation extended to 230 km. Molecular work is underway to characterize the genetic makeup of these social structures. Understanding the invasion status of LFA now may be our most powerful tool in preventing future introductions into USA.