-The objective of this work was to evaluate the natural attack by Acromyrmex crassispinus in initial Pinus taeda plantations without control measures against ants, as well as the effect of defoliation in seedlings of P. taeda. Evaluations of the attack of leaf-cutting ants on P. taeda plantations were done monthly in the first six months, then 9 and 12 months after planting. The percentages of plants that were naturally attacked by ants were registered. The effect of defoliation was evaluated by artificial defoliation, simulating the natural patterns of attack by A. crassispinus on P. taeda seedlings. The natural attack of A. crassispinus was greater during the first months after planting, being more intense in the first 30 days. Artificial defoliation indicated that there were no significant losses in diameter and height in plants with less than 75% defoliation. However, there were significant losses in diameter and height in plants with 100% defoliation, independently of the cut of the apical meristem, and also plant death. The control of leaf-cutting ants in P. taeda plantings, in which A. crassispinus is the most frequent leaf-cutting ant, should be intense only at the beginning of planting, since the most severe attacks occur during this time.Index terms: Acromyrmex crassispinus, Pinus taeda, artificial defoliation, forest pest. Ataque de formigas cortadeiras em plantios iniciais de pinus e crescimento de plantas desfolhadasResumo -O objetivo deste trabalho foi avaliar o ataque natural de Acromyrmex crassispinus em plantios iniciais de Pinus taeda sem controle contra formigas, bem como o efeito da desfolha em mudas de P. taeda. As avaliações do ataque de formigas cortadeiras em plantios de P. taeda foram realizadas mensalmente nos primeiros seis meses, depois aos 9 e 12 meses após o plantio. As percentagens de plantas naturalmente atacadas por formigas foram registradas. O efeito da desfolha foi avaliado por meio do desfolhamento artificial, ao se simularem os ciclos naturais de ataque de A. crassispinus em mudas de P. taeda. O ataque natural de A. crassispinus foi maior nos primeiros meses após o plantio, tendo sido mais intenso durante os primeiros 30 dias. A desfolha artificial indicou que não houve perdas significativas no diâmetro e na altura de plantas com menos de 75% de desfolha. No entanto, observaram-se perdas significativas no diâmetro e na altura de plantas 100% desfolhadas, independentemente do corte da gema apical, e também a morte de plantas. O controle de formigas cortadeiras em plantios de P. taeda, em que A. crassispinus é a formiga cortadeira mais frequente, deve ser intenso somente no início do plantio, pois os ataques mais severos ocorrem neste período.Termos para indexação: Acromyrmex crassispinus, Pinus taeda, desfolha artificial, praga florestal.

The objective of this study was to investigate the seasonal change in the pattern of foraging activity in the leaf-cutting ant Atta capiguara and to provide an estimate of the annual herbivory rate of its colonies. We surveyed at least once a month during 12 months, the foraging activity of two colonies located in a pasture of central Brazil. Each survey consisted in counting the number of ants exiting and returning (laden or unladen) to their nests during 10 min every hour during 24 h. The air temperature and relative humidity were noted at the beginning of each survey. Independent of the season, the colonies presented two peaks of foraging activity, one small peak at the beginning of the day and another peak at the end of the day. During the dry season, the diurnal activity ceased almost completely between 10:00 and 16:00. The proportion of ants returning to the nest laden with a leaf fragment was also lower than during the humid season. Activity rhythm depended significantly on both air temperature and humidity: foraging activity peaked when the temperature was around 25°C and relative humidity around 66 %. Based on the statistical model used to describe the activity rhythm, we estimated that over a period of 1 year, the total dry biomass of vegetation collected by the two colonies studied was, respectively, 25.16 kg for the bigger nest, and 11.69 kg for the smaller one, or an equivalent of 104.83-kg and 48.71-kg fresh biomass, respectively.

Leaf-cutting ants are widely distributed in Brazil, particularly species of the genus Atta. We therefore described the occurrence of leaf-cutting and grass-cutting ant species of the genus Atta. Five routes comprising some of the main highways in the South, Southeast, Center-West, and North of Brazil were sampled, in addition to ants received from other 82 municipalities, composing 300 municipalities sampled. This is the first comprehensive study of Atta in Brazil. The following species were found: A. laevigata, A. capiguara, A. sexdens rubropilosa, A. sexdens piriventris, A. sexdens sexdens and A. cephalotes. Atta laevigata and A. capiguara were the species present in the largest number of the Brazilian municipalities sampled. Atta laevigata assumed the position of species of greatest occurrence in the Brazilian territory. Atta sexdens piriventris was only recorded in the southern region of Brazil. Atta bisphaerica presented lower expansion than A. capiguara. Atta cephalotes and Atta opaciceps are species of very restricted occurrence. Southeastern region was characterized by the occurrence of A. capiguara and A. laevigata. Atta laevigata exhibited a generalized pattern of occurrence in the Center-West and North. Our study contributes to a better understanding of the so far unknown occurrence of leaf-cutting and grass-cutting ants within Brazil.

Acromyrmex balzani is a grass-cutting ant species frequently found in Cerrado areas. However, little is known about the architecture of the polydomous nests of this ant. Fifteen A. balzani nests located in a cerrado region in Botucatu, São Paulo, Brazil, were studied. The polydomous nests were studied in three ways. First, we investigated the architecture in nests moulded with cement and without moulding. Second, we performed an aggressiveness test among workers in different subnests and nests. Third, we excavated the nest and collected the colony to measure the population, verifying the existence or not of a queen in all nests. A cement mould was made of seven nests to permit better visualization of internal structures such as chambers and tunnels. Eight nests were excavated without moulding and white neutral talc was used to highlight the parts of the nests. After excavation, the depth and dimensions (length, width and height) of the chambers were measured. The results showed that the nests had a single entrance hole whose structure consisted of straw and other plant residues in winter. Mounds of loose soil, if present, were found 6-48 cm from the hole. The number of chambers containing fungus ranged from one to five, with the first being found a few centimetres beneath the ground surface (4 cm) and the last up to a maximum depth of 160 cm. The length of the tunnels ranged from 12 to 28 cm. These tunnels were built in a vertical or inclined position, leading to the chambers. No waste chambers were found, with the waste being deposited externally. Additionally, the polydomous nests contained one to eight subnests. In the aggressiveness test, when concolonial workers were confronted, no aggressiveness was observed. In contrast, when allocolonial workers were confronted, there was a high incidence of aggression among them. Excavation of polydomous nests showed only one queen for each polydomous nest, i.e. subnests with a single queen. Our study contributes to a better understanding of the so far unknown nest architecture of the polydomous grass-cutting ant A. balzani.

Atta capiguara is a grass-cutting ant species frequently found in Cerrado biome. However, little is known about the giant nest architecture of this ant. In this study, we investigated the architecture of three A. capiguara nests from a fragment of Cerrado in Botucatu, São Paulo, Brazil. Casts were made of the nests by filling them with cement to permit better visualization of internal structures such as chambers and tunnels. After excavation, the depth and dimensions (length, width, and height) of the chambers were measured. The results showed the shape of Atta capiguara nests consisting of mounds of loose soil with unique features resembling a conic section. The fungus chambers were found distant from the mound of loose soil and were spaced apart and distributed laterally at the soil profile. The waste chambers were located beneath the largest mound of loose soil. Both the fungus and waste chambers were separated and distant. Our study contributes to a better understanding of the so far unknown nest architecture of the grass-cutting ant A. capiguara.