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

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.

Carbon dioxide levels in initial nests of the leaf-cutting ant Atta sexdens (Hymenoptera: Formicidae).

Claustral foundation of nests by Atta sexdens Forel (Hymenoptera: Formicidae) involves great effort by its queens, solely responsible for the cultivation of the fungus and care for her offspring at this stage. The minimum workers, after 4 months, open access to the external environment to foraging plants to cultivate the symbiotic fungus, which decomposes the plant fragments and produces gongilidea nodules as food for the individuals in the colony. Colony gas exchange and decomposition of organic matter in underground ant nests generate carbon dioxide (CO2) emitted into the atmosphere. We described the carbon dioxide concentration in colonies in the field. The objective was to evaluate the carbon dioxide concentration in initial A. sexdens colonies, in the field, and their development. The CO2 level was also measured in 4-month-old colonies in the field, using an open respirometric system fitted with an atmospheric air inlet. The CO2 level of the respirometric container was read by introducing a tube into the nest inlet hole and the air sucked by a peristaltic pump into the CO2 meter box. The CO2 concentration in the initial colony was also measured after 4 months of age, when the offspring production (number of eggs, larvae, pupae and adult workers) stabilized. Ten perforations (15 cm deep) was carried out in the adjacent soil, without a nest of ants nearby, to determine the concentration of CO2. The composition of the nests in the field was evaluated after excavating them using a gardening shovel and they were stored in 250 ml pots with 1 cm of moistened plaster at the bottom. The CO2 concentration was higher in field nest than in adjacent soil. The concentration of carbon dioxide in A. sexdens nests in the field is higher than in those in the soil, due to the production of CO2 by the fungus garden and colony.

Contamination routes and mortality of the leaf-cutting ant Atta sexdens (Hymenoptera: Formicidae) by the insecticides fipronil and sulfluramid through social interactions.

BACKGROUND: Leaf-cutting ants (LCAs) of the genera Atta and Acromyrmex (Hymenoptera: Formicidae) are important pests of forest plantations, agriculture and livestock. Toxic baits containing the active ingredients fipronil or sulfluramid are the main method used to control LCAs. Insecticide dispersion among members of an LCA colony during control with toxic bait is not well understood. The objective of the study was to determine whether self-grooming, allogrooming or touching behavior among Atta sexdens (Hymenoptera: Formicidae) workers disperses the insecticides fipronil and sulfluramid among members of the colony. The insecticides were topically applied on groups of A. sexdens workers and social interactions between ants with and without insecticide, and group mortality were evaluated. RESULTS: Behavioral analysis showed an increase in interaction among LCA workers as the numbers of individuals increased, with touches between workers being the most frequent behavior. The frequency of observed behaviors was higher in groups treated with sulfluramid compared with fipronil. The mortality of groups treated with fipronil was almost twice as high compared with ants treated with sulfluramid. The insecticides are probably dispersed by excessive touching among workers and subsequent self-grooming and allogrooming. CONCLUSION: These behaviors were responsible for the rapid dispersion of insecticides among members of the colony. Corroboration of the hypothesis that social interactions contaminate nestmates is a model for future studies on contamination of ant workers with active insecticide ingredients. © 2021 Society of Chemical Industry.

Chemical control of leaf-cutting ants: how do workers disperse toxic bait fragments onto fungus garden?

ABSTRACT Leaf-cutting ants are controlled with toxic baits. For the method's greater efficiency, the baits must be distributed and processed by workers during fungus cultivation. To test hypotheses whether the mode of action of the active ingredients, which blocks the sodium channels and interrupts the production of ATP in the mitochondria, interferes with fragment distribution in nests; the dispersion of pellets fragments during fungus cultivation by workers was assessed, spatially referencing the fragment onto the fungus garden. Pellets fragments were randomly distributed, but the amount pellets fragments was influenced by the way that the active ingredient acts in the colony.