The introduction of the fire ant parasitoid Pseudacteon nocens in North America: challenges when establishing small populations

Several species of parasitoid phorid flies (Pseudacteon spp., Diptera: Phoridae) have been released into the United States as potential biological control agents for the red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae). Here we report the first successful introduction and spread of Pseudacteon nocens Borgmeier at a site in Texas, USA. Pseudacteon nocens is an important natural enemy since it is a widespread and often abundant parasitoid of S. invicta in Argentina, where it attacks larger fire ant workers eliciting a strong defensive response. Several years of effort to establish this species previously failed, and here we provide a model to better understand the likelihood of founding new populations when introducing sequential batches of flies in field or laboratory cultures. We also report on a novel method of establishing new populations of phorids in the field using pupae burial boxes to overcome constraints of releasing adult flies or infected worker ants.