Field evaluation of fipronil and chlorfenapyr for management of odorous house ants (Hymenoptera: Formicidae)

Abstract:
Odorous house ant, Tapinoma sessile Say, is a pest ant with global distribution. The common name is derived from the emission of a substance with an odor similar to that of butyric acid. Polygynous colonies often associated with notably dynamic populations and multiple nesting sites make odorous house ants a formidable opponent upon gaining entry to a structure. This paper examines the use and performance of two non-detectable chemistries with distinctive use patterns governed by their respective Federal label registrations. Termidor® (fipronil) applications are applied perimeter only and to areas of entry and or egress of a structure; while Phantom® (chlorfenapyr) applications are limited to spot and crack and crevice sprays to indoor sites exclusively. Chlorfenapyr received registration for treatment of outdoor usage patterns of entry and or egress similar to that of fipronil. Such treatment regimes were not used during the course of these trials. Single occupied dwellings of varying dimensions, each with robust exterior and interior infestations were selected for treatment with either fipronil 0.06% dilution sprays alone (exterior) or fipronil 0.06% + chlorfenapyr 0.50% interior spot crack and crevice sprays. Amount of fipronil applied was based upon the 1.5 gals per 1000 sq. ft. label language standard as a 1’ vertical and 1’ horizontal surface exterior perimeter spray. Easily accessible areas providing entry and or egress of ants were also subject to the prepared solutions. Static or increasing populations of odorous house ants after treatment with fipronil was the major parameter used to dictate the use of chlorfenapyr. Amount of chlorfenapyr delivered to subject sites was measured in milliliters and directed sprays were applied to run-off. One-way traffic counts taken prior to treatment served as baseline counts where trails entered into the test sites. Subsequent counts from these same sites were used to assess the performance of the treatments. Ant count data was taken at 1 day and 1, 2, 4 and up to 8 weeks or more post application. Total number of ants observed on all trails in a 10 minute inspection of the structures exterior and interior was recorded during these evaluation intervals.