Comparison of Different Protocols for Control of the Red Imported Fire Ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), in Orange County, California, Including a List of Co-occurring Ants

The Orange County Vector Control District treats infestations of red imported fire ants, Solenopsis invicta Buren, with two granular baits, Amdro Pro and Distance, at residences with the ant. Some treatments are subcontracted to pestmanagement professionals who received red imported fire ant certification by the Orange County Vector Control District. During this study, we compared four treatment protocols and assessed their efficacy at suppressing red imported fire ants. At the first post-treatment survey at 3 months, homes in three of the protocols received a single treatment of Amdro Pro. Homes in two of the protocols subsequently received either one follow-up treatment with Distance at 3 months or two follow-up treatments with Distance at 3 and 6 months, respectively. Homes in the fourth protocol received a single treatment of a 50:50 mixture of Amdro Pro and Distance. Most reinfestation by red imported fire ants occurred within the first 3 months after the initial treatment, with failure ranging from 29–40%. Although the failure rate was slightly higher for the treatment with the mixture compared to Amdro Pro alone (40 versus 33%, respectively), failure rates did not differ significantly between these treatments. Thereafter and until 9 months later, treatment failures were <10% among residences without red imported fire ants at 3 months. The differences among the protocols were not significant for any of the time periods. At 9 months, there was a small increase in failures compared to 6 months, indicating more red imported fire ants had moved in from surrounding areas or the original colonies were starting to recover. Additional treatments would be necessary to maintain a low level of infestation. We also recorded the identification and frequency of other ant species seen at homes inspected for red imported fire ants.