A key factor contributing to the decline in the population of Pisonia grandis on Rose Atoll is an infestation of the non-native scale, Pulvinaria urbicola (Homoptera: Coccidae). Ants, in facultative relationships with scale insects, may facilitate scale population growth and increase their effect on plant hosts. Three ant species found on Rose Atoll, Tetramorium bicarinatum, T. simillimum, and Pheidole oceanica, are capable of tending Pulvinaria on Pisonia and may have contributed to the demise of the trees on the atoll. Replicated trials conducted on Rose Atoll during 17–21 March 2013 tested the effectiveness and relative attractiveness of five formicidal baits potentially to be used to eradicate these ants on the atoll. Three baits contained toxins (hydramethylnon in Amdro® and Maxforce®, indoxacarb in Provaunt®) and two baits contained an insect growth regulator (IGR; pyriproxyfen in Distance® and s-methoprene in Tango®). Amdro, Distance, and Maxforce are granular baits while Provaunt and Tango were mixed with adjuvants to form a gel-like matrix. Results varied among ant species and baits, but Provaunt was highly effective against workers of both Tetramorium species while Amdro and Maxforce were highly effective against T. simillimum and P. oceanica. Limited time on the island prevented the evaluation of the effectiveness of the IGR baits. The relative attractiveness of the baits generally mirrored their ability to kill worker ants. Tetramorium simillimum was attracted to all five baits; T. bicarinatum was attracted to Provaunt, Distance, and Tango; and P. oceanica was attracted to the three granular baits. These results and the small area of Rose Atoll suggest that island-wide application of formicidal baits may result in eradication of these ants, but an application strategy targeting all three species would more likely succeed with the use of multiple baits.
