Evidence of social facilitation and inhibition in digging behavior of red imported fire ants, Solenopsis invicta

Authors: Chen, Jian

Submitted to: Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2020
Publication Date: 3/19/2020
Citation: Chen, J. 2020. Evidence of social facilitation and inhibition in digging behavior of red imported fire ants, Solenopsis invicta. Insect Science. https://doi.org/10.1111/1744-7917.12781.
DOI: https://doi.org/10.1111/1744-7917.12781

Interpretive Summary: Digging behavior is critical to the survival of the fire ant colonies since digging is one of fundamental behaviors involved in building nest and foraging tunnels. The volume of a fire ant nest is directly proportional to the colony total ant population. In other words, fire ants are able to assess the volume of their nest and precisely regulate their digging behavior. We do not know how fire ant achieve that. In this study, digging behavior of fire ants was studied using sand as a digging substrate. When the group size is small, grouped ants often had higher digging amount per individual than an ant in solitary, indicating that social facilitation occurred among ants. However, while group size increased further, the digging amount per ant decreased, indicating digging inhibition took place. Ants preferentially dug the sand treated with worker body extracts over the untreated sand and more ants were found in the treatment at the end of experiment. The body extract also significantly increased the percentage of ants that showed digging effort. These results indicate that chemical cues may play a role in social facilitation of digging behavior in red imported fire ants; however, these data can’t explain the social inhibition observed in this experiment. In order to understand how fire ants regulate their nest volume, the mechanisms behind the observed social facilitation, social inhibition and their transition must be elucidated.

Technical Abstract: As a mound building species, digging is an intrinsic behavior of the red imported fire ants, Solenopsis invicta Buren. In this study, digging behavior of S. invicta was studied using sand as a digging substrate. When the group is small, grouped ants often had a significantly higher digging amount per individual than an ant in solitary, indicating that social facilitation occurred among ants. However, with ant numbers increased further, the digging amount per ant decreased, indicating digging inhibition took place. Ants preferentially dug the sand treated with worker body extracts and more ants were found in the treatment at the end of experiment. The body extract significantly increased the percentage of ants that showed digging effort. These results indicate that chemical cues may play a role in social facilitation of digging behavior in red imported fire ants; however, these data can’t explain the social inhibition observed in this experiment. The mechanisms behind the social facilitation, social inhibition and their transition require further investigation.