The ideal habitat for leaf-cutting ant queens to build their nests

Abstract

Queens of Atta sexdens Forel (Hymenoptera: Formicidae) face biotic and abiotic environmental factors in the environment while establishing their nests. Biotic factors such as predation, microbial pathogens, successful symbiotic fungus regurgitation, excavation effort and abiotic factors such as radiant sunlight, temperature, density, and soil moisture exert selection pressures on ant queens. Biotic factors such as temperature and solar irradiation affect the survival of the initial colony differently, in different environments in the field. Queens of the leaf-cutting ant A. sexdens, were installed in sunny and shaded conditions to test this hypothesis. Two hundred A. sexdens queens were collected and individualized in two experimental areas (sunny and shaded), each in an experimental area (25 m²) in the center of a square (50 × 50 cm). Temperature, irradiance, nest depth, rainfall and queen mortality were evaluated. Atta sexdens colony development was better in the shaded environment, and the depth and volume of the initial chamber, fungus garden biomass and number of eggs, larvae, pupae and workers were greater. The queen masses were similar in both environments but mortality was higher in the sunny environment. The worse parameter values for A. sexdens nests in the sunny environment are due to the greater solar irradiance, increasing the variation range of the internal temperature of the initial chamber of the nest. On the other hand, the more stable internal temperature of this chamber in the shaded environment, is due to the lower incidence of solar irradiance, which is also more advantageous for queen survival and the formation and development of A. sexdens colonies. Shaded environments are a better micro habitat for nesting A. sexdens than sunny ones.

Figure 1

Temperature and irradiance over the first 4 months of Atta sexdens (Hymenoptera: Formicidae) nests in sunny and shaded environments. Willmott similarity index between irradiance and inside and outside temperatures (a) and between outside and inside temperatures (b) in sunny and shaded environments. (N = sample size).

Figure 2

Development of Atta sexdens (Hymenoptera: Formicidae) nests in a sunny and shaded environments over 4 months (a, b) and 4-month average of biology (c) and mortality (d).