Does the red imported fire ant (Solenopsis invicta) effect weed seed predation?

Seed removal under natural (high Solenopsis invicta population) and treated conditions (Solenopsis invicta removed with Amdro ® [hydramethylnon]) were monitored in an Eastern North Carolina soybean field during October 2011. 30 meter by 30 meter plots were established and ant populations were estimated with hotdog/test-tube traps and pitfall traps. High resolution video monitoring equipment was used to determine what organisms were responsible for weed seed predation under the high and low ant conditions. Five seeds of three common weed species (redroot pigweed [Amaranthus retroflexus], broadleaf signalgrass [Urochloa platyphylla], and sicklepod [Senna obtusifolia]) were monitored for three hours during the day and for three hours at night for three consecutive days. Solenopsis invicta was not seen removing or consuming any of the three weed seed species. Instead, field crickets (Gryllus sp.) and house mice (Mus musculus) were the predominant weed seed predators. Carabid beetles, such as Harpalus pennsylvanicus, which are common weed seed predators in temperate areas, were rarely seen in the videos or in the pitfall traps.  House mice were especially common in the plots where ants had been removed. These results show that while Solenopsis invicta has become a dominant insect in the Southeast United States, they do not contribute to weed seed predation ecosystem services in agricultural settings.  Instead, they may weaken this service by displacing other seed eating organisms such as mice and beetles.