Red imported fire ants (Hymenoptera: Formicidae): population dynamics following treatment with insecticidal baits.

Abstract

Evaluation of Solenopsis invicta Buren populations following insecticidal bait treatments is usually made on the basis of presence or absence of active nests. An alternative method is described in which population densities are based on total worker ants per hectare. Using these two methods, we found that there was essentially no difference in population levels of treated and untreated plots 27 to 36 months after application of two baits. In a more detailed study in which imported fire ant colonies were monitored for 156 weeks, the number of ant colonies had increased 327% after 44 weeks; however, the total number of ants in these same colonies was still 84% below pretreatment numbers. These data reflect the great difference in size of mature pretreatment colonies and small incipient posttreatment colonies. Based on the total ant population method, total ant numbers remained below that in the check area for 2 years. Thus, effective control of the pest extended well beyond that indicated by the nest count method.