Fatores endógenos e exógenos influenciam o forrageamento de colônias de Atta sexdens Linnaeus,1758 (Hymenoptera: Formicidae)?

Abstract

Leaf-cutting ants are social insects and are positively associated with important ecological processes such as forest regeneration, soil aeration, seed dispersal, organic matter fragmentation, nutrient cycling. On the other hand, they are considered one of the most important herbivores in the Neotropical region and some species have great agricultural and forest importance. The foraging of leaf-cutting ants is a very complex activity and is influenced by exogenous factors such as temperature, humidity, precipitation and also endogenous factors such as the presence of the young, presence of queen and nutritional status of the mutualistic fungus. Such factors can influence foraging activities and the performance of Atta sexdens colonies and their ecological functions. In the first part of this work, we sought to understand how some endogenous factors, such as the presence of the queen and larvae and pupae, influence the foraged mass and the conversion of the vegetal mass into symbiotic fungus in the laboratory. Small colonies with and without queen were used and forage mass, fungus volume and worker mortality were evaluated for 120 days. It was found that the presence of the queen does not influence the daily amount of foraged mass, but it positively influences the accumulated amount and the volume of symbiotic fungus produced and negatively the mortality of workers. Although the colonies present the same foraging pattern, the absence of the queen can reduce the total activity of the colony in comparison with colonies with queen, thus, the use of colonies without queen in foraging studies for a long period of time can cause an underestimation of observed activities. In the second part, it was verified that an exogenous factor, such as temperature, influences the walking speed of workers, the size of the vegetable mass transported and the mass of the forage worker. For this purpose, an adult colony of A. sexdens was used in the laboratory and connected to a foraging source with a temperature ranging from 10 to 40°C. It was found that the walking speed and the dry mass of the vegetable fragments carried by the workers of Atta sexdens increase with increasing temperature and that the foraging time does not influence the size of the fragments carried by the workers. It was also found that the dry masses and widths of the workers' cephalic capsules are higher at all temperatures, except at 28 ° C and that the foraging time also does not influence the size of the foraging workers. These results show that endogenous and exogenous factors influence the behaviour and foraging performance of leaf-cutting ants, inducing adaptations of the colony to ensure their survival.