Waste of leaf-cutting ants: disposal, nest structure, and abiotic soil factors around internal waste chambers

Abstract

Leaf-cutting ants produce large quantities of waste that harbor bacteria and fungi that are harmful to the colony. To be protected from these pathogens, the workers of Atta species present a sophisticated organization to manage harmful material, which can be deposited outside the nest or in internal chambers. However, little is known about the behavior of Acromyrmex species in handling and disposal of waste. Due to some observations, we assume that the same species of Acromyrmex can deposit waste outside the nest and into internal chambers and raise the following question: what determines the occurrence of internal waste chambers in Acromyrmex? To address this question, we verified whether nest depth influences the waste-chamber occurrence. We also verified the nest structure and the abiotic factors of soil beside each waste-chamber: pH and water content of the soil. For this, eight nests were excavated for Acromyrmex balzani and Acromyrmex rugosus rugosus. We verified that not only can the same leaf-cutting ant species deposit debris both outside and inside the nest but also the same nest can present internal chambers and external waste deposit. The soil beside the waste chamber always presented an acidic pH, while the humidity varied widely. Our results showed that the nest depth was highly correlated with the depth of the waste chamber (p = 0.0003) and probably has some influence on waste disposal. The characteristics of the nest and the role of depth in the choice of waste chamber location are discussed.

Destructive disinfection of infected brood prevents systemic disease spread in ant colonies

“…Additionally, they are highly territorial and forage mostly in the area around their nests, meaning that if they do not clear it of dead and potentially infectious nestmates, they are likely to be reencountered ( Boomsma et al, 2005 ; Cremer et al, 2017 ). Ants tend therefore to place corpses onto specific midden (trash) sites that are located inside or outside near the nest, but these sites are still regularly visited by midden workers ( Verza et al, 2017 ; Hart and Ratnieks, 2002 ; Farji-Brener et al, 2016 ). Consequently, although middens likely reduce a colony’s exposure to corpses, they still represent a potential route for disease transmission back into the colony; hence the need to destroy infected corpses rather than simply taking them out of the nest.…”

Destructive disinfection of infected brood prevents systemic disease spread in ant colonies

“…Additionally, they are highly territorial and forage mostly in the area around their nests, meaning that if they do not clear it of dead and potentially infectious nestmates, they are likely to be reencountered (Boomsma et al, 2005;Cremer et al, 2017). Ants tend therefore to place corpses onto specific midden (trash) sites that are located inside or outside near the nest, but these sites are still regularly visited by midden workers (Verza et al, 2017;Hart and Ratnieks, 2002;Farji-Brener et al, 2016). Consequently, although middens likely reduce a colony's exposure to corpses, they still represent a potential route for disease transmission back into the colony; hence the need to destroy infected corpses rather than simply taking them out of the nest.…”

Prophylactic Avoidance of Hazardous Prey by the Ant Host Myrmica rubra

“…This is namely achieved through an organisational immunity which basically relies on a spatial and social segregation between potential vectors of pathogens such as foragers and individuals of the utmost importance for the colony future, such as the queen or the larvae (ants: [ 18 ], bees: [ 19 ], reviewed in [ 20 ]). Such a hygienic distancing also applies for organic waste (e.g., food remains, faeces) [ 21 , 22 ] or dead nestmates (ants: [ 23 , 24 , 25 ], bees: [ 26 , 27 ], bumble bees: [ 28 ], reviewed in: [ 29 , 30 ]) which are actively discarded by nest cleaners and undertakers. Likewise, moribund workers, close to death, self-exclude from their colony by exiting the nest and die in social isolation far from their nestmates (ants: [ 31 , 32 ], bees: [ 33 ]).…”