Agent-based Bayesian spread model applied to red imported fire ants in Brisbane

Red imported fire ants were first detected in Brisbane in February 2001. Since then, the National Red Imported Fire Ant Eradication Program has been collecting data on the locations of detected nests and keeping a record of the areas searched and treated with baits. The result is an exceptionally large and detailed record of both the spread of the ant and the effects of human intervention on the invasion. In recent work, these data have been used to reconstruct the history of the invasion in terms of the trajectories of nest abundance and geographic range. A novel feature of the method is that it explicitly models individual nests and can thus reconstruct the invasion to a high level of spatial and temporal detail. Some important lessons have been learned from this reconstruction. One is that an invasion can continue to expand its geographic range despite a drop in the number of invaders. Another is that immature nests - those not yet able to found new nests and generally too small to be detected - outnumbered mature nests at every stage of the invasion. Both of these lessons highlight the importance of sophisticated models to assist in monitoring an invasion and managing an eradication programme.