Light affects the homing ability of Solenopsis invicta (Hymenoptera: Formicidae) foraging workers

Authors: Vander Meer, Robert - Bob; ALONSO, LEEANNE - Former ARS Employee; LOFGREN, CLIFFORD - Retired ARS Employee

Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/27/2023
Publication Date: 10/9/2023
Citation: Vander Meer, R.K., Alonso, L.E., Lofgren, C.S. 2023. Light affects the homing ability of Solenopsis invicta (Hymenoptera: Formicidae) foraging workers. Florida Entomologist. 106(3):175-181 . https://doi.org/10.1653/024.106.0304.
DOI: https://doi.org/10.1653/024.106.0304

Interpretive Summary: Ants make up about 20% of non-human animal biomass and they inhabit a wide variety of ecosystems world-wide. The invasive red imported fire ant impacts many important economic sectors, e.g., households, agriculture, electric and communications. Part of its success is due to their high reproductive rate and population density. Accordingly, this ant has a highly efficient recruitment system that locates and brings back food resources to the colony. Distribution of food to the colony, and recruitment of worker ants to from the colony to large food sources is understood; however, how the foraging workers after finding food resources find their way back to the colony has not been elucidated until now. Foraging workers can keep track of where they are from their home colony using a relatively fixed light source. If a light source is removed from the foraging arena their time to trail formation at a food source is greatly retarded or it does not happen. This research adds to our knowledge of why fire ants are so efficient finding and retrieving needed resources and may yield methods to disrupt this efficiency.

Technical Abstract: Ant species have evolved a wide range of mechanisms to locate food resources and to distribute them to the colony. Two major components are involved: 1) scout worker ants leave the nest and randomly forage an area for resources and 2) the scout must orient back to its nest after food discovery either with food or to recruit workers to a food source too large for a single forager to take back to the colony. Fire ant, Solenopsis invicta, recruitment has been well studied behaviorally and chemically. However, initial homing of the foraging worker back to its colony after food discovery only has been investigated relative to the sensitivity of the ant to geomagnetism under dark conditions. Here, we focus on dark/light in the context a homing cues used by foraging workers above ground. We demonstrated that fire ants use light as a powerful homing/orientation cue that allows them to orient back to their nest after locating food, instead of retracing their previous random foraging path. The light source needs to be relatively fixed (rotating light inhibited trail formation), and it does not have to be very bright, since there was no degradation of homing ability even at 1 lux (equivalent to moon light). We also showed time-to-trail-formation under red light was indistinguishable from the dark condition. An experiment that changed the visual cues but kept the light fixed, suggested that in the presence of a light source changing visual cues have no effect on fire ant homing. Our study documents the use of light in fire ant homing and contributes to our understanding of one component of the complex fire ant recruitment system.