Lee, C.-C., Lin, Y.-T., Chiu, M.-C., Yang, C.-C.S. & Lin, C.-C.

Preferential food allocation to an essential worker subcaste in the invasive yellow crazy ant, Anoplolepis gracilipes (Hymenoptera: Formicidae)

Inside ant colonies, food distribution could be a complex behavioral process as its pattern and flow differ largely across contexts and are governed by multiple factors such as starvation level, colony size, and participating castes. However, little is known about how the food flow is regulated among worker subcastes. In the current study, we characterized the flow of dyed food between donors (foraging workers) and two in-nest worker subcastes (intra-nidal normal and physogastric workers) in the invasive yellow crazy ant, Anoplolepis gracilipes. Physogastric workers are an essential worker subcaste in A. gracilipes as they produce trophic eggs that constitute a major diet for larvae. We therefore hypothesized that physogastric workers may have a trophic advantage over intra-nidal workers as adequate nutrient intake is critical for sustainable trophic egg production. Our behavioral observations revealed that higher proportions of dyed-foodcontaining individuals were consistently found in the physogastric worker subcaste than other worker subcastes, irrespective of the macronutrient type consumed by donors. Although donors engaged in trophallaxis with intra-nidal workers more frequently than with physogastric workers, significantly higher proportions of physogastric workers were found to have dyed food in their crops 24 hours after the experiment completion. None of the larvae were detected with dyed food over the entire observation period, supporting the previous finding that food allocation to larvae in this ant species occurs primarily via trophic eggs instead of worker-to-larva trophallaxis. These results are consistent with our prediction that physogastric workers represent a “trophic center” to which food is preferentially allocated, possibly for optimization of their task performance. This study highlights the critical role of physogastric workers in the colony of this highly invasive ant and offers insights into the future development of the pest management strategy.

Open access, licensed under CC BY 4.0. © 2022 The Author(s).

Lee, C.-C., Lin, Y.-T., Chiu, M.-C., Yang, C.-C.S. & Lin, C.-C.

Preferential food allocation to an essential worker subcaste in the invasive yellow crazy ant, Anoplolepis gracilipes (Hymenoptera: Formicidae)

Inside ant colonies, food distribution could be a complex behavioral process as its pattern and flow differ largely across contexts and are governed by multiple factors such as starvation level, colony size, and participating castes. However, little is known about how the food flow is regulated among worker subcastes. In the current study, we characterized the flow of dyed food between donors (foraging workers) and two in-nest worker subcastes (intra-nidal normal and physogastric workers) in the invasive yellow crazy ant, Anoplolepis gracilipes. Physogastric workers are an essential worker subcaste in A. gracilipes as they produce trophic eggs that constitute a major diet for larvae. We therefore hypothesized that physogastric workers may have a trophic advantage over intra-nidal workers as adequate nutrient intake is critical for sustainable trophic egg production. Our behavioral observations revealed that higher proportions of dyed-foodcontaining individuals were consistently found in the physogastric worker subcaste than other worker subcastes, irrespective of the macronutrient type consumed by donors. Although donors engaged in trophallaxis with intra-nidal workers more frequently than with physogastric workers, significantly higher proportions of physogastric workers were found to have dyed food in their crops 24 hours after the experiment completion. None of the larvae were detected with dyed food over the entire observation period, supporting the previous finding that food allocation to larvae in this ant species occurs primarily via trophic eggs instead of worker-to-larva trophallaxis. These results are consistent with our prediction that physogastric workers represent a “trophic center” to which food is preferentially allocated, possibly for optimization of their task performance. This study highlights the critical role of physogastric workers in the colony of this highly invasive ant and offers insights into the future development of the pest management strategy.

Open access, licensed under CC BY 4.0. © 2022 The Author(s).