Do soil density and humidity affect nest‐founding in leaf‐cutting ant queens?

• Published in: Entomologia experimentalis et applicata Vol. 170; no. 7; pp. 623 - 628
• Main Authors: Sousa, Kátia K. A., Camargo, Roberto S., Caldato, Nadia, Farias, Adriano P., Matos, Carlos A. O., Zanuncio, José C., Forti, Luiz C.
• Format: Journal Article
• Language: English
• Published: Amsterdam Wiley Subscription Services, Inc 01-07-2022
• Subjects: Abiotic factors; Atta sexdens; Attini; Chambers; Cuttings; Density; Energy expenditure; Environmental conditions; Excavation; excavation effort; Formicidae; habitat choice; Habitats; Humidity; Hymenoptera; Leaves; Moisture content; Moisture effects; Mortality; Myrmicinae; nest sites; Pasture; Queens; Soil density; soil humidity; Soil moisture; Soil temperature; Soils; Water content
• ISSN: 0013-8703; 1570-7458
• DOI: 10.1111/eea.13180

The habitat choice of nest sites by founding queens of leaf‐cutting ants varies with abiotic factors such as temperature, soil density, and soil humidity. In this study, we tested the hypothesis that soil density and moisture affect excavation effort (i.e., excavation period, excavated soil amount, initial nest depth, initial chamber volume, and mortality) in queens of the leaf‐cutting ant Atta sexdens (L.) (Hymenoptera: Formicidae). Queens were placed in experimental areas in three natural soils in Brazil with varying density and moisture content. The excavated soil was collected, dried, and weighed, and digging period, nest depth, chamber volume, and queen mortality were evaluated after nest establishment. In artificially shaded habitats (less dense and more humid soil), the establishment of queens was greater, the period of nest foundation was shorter, and excavated soil amount, nest depth, and volume of the initial chamber were greater than in forest and pasture habitats (denser and drier soils). Also, queen mortality was lower in less dense, more humid soil. This indicates a trade‐off between maximizing the depth of the nest, to increase protection against inadequate environmental conditions, and minimizing energy expenditure during excavation, affecting their survival.
Leaf‐cutting ant queens dig the soil to the ideal depth to found their nest. In a field study, we assessed whether soil density and moisture affect nest excavation parameters of Atta sexdens (Hymenoptera: Formicidae). Nest‐digging took more time in forest and pasture habitats (denser and drier) than in artificially shaded habitats. However, nest volume and depth were greater in artificial shade, and queen mortality was lower. This indicates a trade‐off between maximal nest depth (i.e., safety) and queen energy expenditure.