Food search and transport in red imported fire ants (Hymenoptera: Formicidae) under wet conditions

Abstract

The red imported fire ant, Solenopsis invicta Buren, has invaded various wetlands such as beaches, swamps, and mangrove forests. We hypothesize that S. invicta can effectively forage food in these habitats. Here, the food searching and transport by S. invicta on each substrate (sand or soil with freshwater or artificial seawater) at different saturation levels (70%, 100%, 130%, or 160%) were evaluated. Ants walked on unsubmerged substrates (70%- and 100%-saturated) to search for food, and surprisingly, they swam and passed 130%- or 160%-saturated substrates that were submerged with thin layers of water. Saturation level may significantly affect duration of food search and/or transport, depending on substrate types. The number of foraging ants rapidly increased and decreased on the food-releasing platform located on the 70%-saturated substrate and remained stable on the platform located on the 100%-saturated substrate. However, only a few ants were found on the platform located on waterlogged substrates throughout the experiment. In addition, no food was successfully transported passing the waterlogged substrate. We also compared food search and transport among four substrates (sand or soil with freshwater or seawater) at the 70%- or 100%-saturation level. Ants spent similar time searching for food and transporting food on the platform, but minimal food was transported passing the soil with freshwater or seawater. Our results showed that S. invicta can successfully search for food but fail to transport food on waterlogged substrates. In addition, both substrate types and saturation level affected food transport under unsubmerged conditions.