Leaf-cutting ants Atta, known as saúvas, are important animals for the functioning of
ecosystems, since, directly or indirectly, they help in the cycling of nutrients. Because they are polymorphic, the colony is divided into castes. Workers from the foraging caste transport vegetal fragments (loads) up to their nests to serv as substract to a symbiont fungus. A positive correlation has already been observed between the size of workers of some species and the size of their loads. In the present study, this relation was investigated for foragers of Atta laevigata and if it changes between day and night shifts and between plant species. Until 60 workers and their respective load were collected in each nest (n = 5) at day and night shift. The weight (mg) of ants (Pf) and their loads (Pc) were obtained on a precision balance. 19 diurnal and 22 nocturnal collections were carried out, when workers foraged different plants: manga (Mangifera indica), dormideira (Mimosa pudica), mamoninha (Mabea fistulifera), castanha (Terminalia catappa), oiti (Moquilea tomentosa), baru (Dipteryx alata), flamboiã (Delonix regia) and jamelão (Syzygium cumini). The worker’s burden (CC = [Pf + Pc]/Pf), which represents the weight that the ant carries in relation to its own weight, and the weights of ants and loads were compared between periods and between foraged plants. 855 ants and their loads were weighed when ants foraged during the daytime and 1139 during nighttime. Pf e Pc (mean ± dp) were greater (F = 84,3; P = 0,001) during daytime (22,4 ± 10,8 and 39,9 ± 34,1) when compared to nighttime (18,4 ± 10,1 and 32,1 ± 29,0). Pearson's correlation showed that the weight of the load increases as the weight of the ant also increases (r2 = 0,37; P = 0,001), but with no difference between periods. The worker's burden was greater (teste H = 9,5; P = 0,002) during nighttime (3,0 ± 1,6) in relation to daytime (2,8 ± 1,3). Burden was greater when workes carried jamelão. In conclusion, both the weight of the workers and the weight of the loads were greater at daytime, and the correlation between the load’s weight and the worker's weight was positive. However, nocturnal workers, especially those carrying jamelão, had a greater burden than workers that foraged during the day.
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