Ecological Archives E096-023-A1

Cause Hanna, Ida Naughton, Christina Boser, Ruben Alarcón, Keng-Lou James Hung, and David Holway. 2015. Floral visitation by the Argentine ant reduces bee visitation and plant seed set. Ecology 96:222–230.

Appendix A. Description of the Argentine ant removal protocol and its efficacy.

In this appendix we describe the treatment protocol for the Argentine ant developed by The Nature Conservancy and the National Park Service for implementation on Santa Cruz Island, California, USA. The protocol used attractive bait matrices, low-toxicity baits and dispersal methods efficient enough to permit large-scale treatment of infested areas, some of which were in rugged terrain or dense vegetation. Treatment baits consist of Optigard® Flex (Syngenta Crop Protection LLC) concentrated at 21.6% thiamethoxam and diluted to 0.0006% thiamethoxam in 25% weight-on-weight sucrose solution. These ingredients are mixed with polyacrylamide crystals (MiracleGro©), which provide physical support for the liquid bait and allow the mixture to be broadcast in small aliquots over a large area. In 2012, treatments ran from June to September and covered approximately 4 ha. During each monthly treatment session, bait was broadcast on the ground in a 2 × 2 m grid throughout the treatment areas; each grid point received approximately 15 mL of bait. During and after monthly treatment (Jun - Sept), ant activity was monitored at 379 fixed points within a systematic bait monitoring grid (20 × 40 m). At each monitoring point, we took three measures of ant activity: abundance at non-toxic baits, abundance in pitfall traps, and abundance at toxicant baits.

The treatment resulted in the rapid and sustained reduction in Argentine ant abundance within the treated area. After the final Optigard Flex bait deployment in September, for example, the abundance of the Argentine was reduced in treatment plots (relative to control plots) by 99.84 ± 0.16% at non-toxic baits and by 99.5 ± 0.37% in pitfall traps. Non-target effects associated with the treatment appeared minimal and were restricted to arthropods. The following arthropods represented the specified percentage of the visitors observed during the 3267 instantaneous toxicant bait counts: ants (94.13%), introduced isopods (5.87%), beetles (0.068%), yellow jackets (0.038%) and earwigs (0.004%). No bees were observed on the baits.

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