Abstract This study provides a list of the ground-dwelling ant species in Nhecolândia, Pantanal, Mato Grosso Sul, Brazil. The Pantanal is the largest tropical wetland in the world and is currently under strong anthropic pressure. Ground-dwelling ants were collected in three sites: (1) a forest regeneration area; (2) a pasture area; and (3) an area of secondary native vegetation. In each site, 120 samples were collected using pitfall traps in the dry and rainy seasons of 2016. Additional samplings were performed with Winkler extractors (30 leaf-litter samples) and manually, also in dry and rainy seasons of 2016. In total, we collected 172 species, which, summed with the additional records from literature, raise the number of ant species recorded in Nhecolândia to 184 in 42 genera and nine subfamilies. Eleven species were recorded for the first time in the state of Mato Grosso do Sul. Also, the survey adds two new species records to Brazil. Besides contributing to the inventory of the ant species present in the Pantanal biome, the present study provides an important resource for future conservation plans for this threatened ecoregion.

Emigração de uma colônia da formiga cortadeira Acromyrmex heyeri Forel (Hymenoptera, Formicidae). A migração de colônias de formigas cortadeiras é um fenômeno pouco estudado. Nesse estudo, nós relatamos a emigração de uma colônia da formiga cortadeira A. heyeri no Brasil. A colônia emigrou 47,5 m de distância do seu ninho original para um novo local, provavelmente porque sofreu um estresse considerável devido à interações competitivas com uma colônia de Acromyrmex crassispinus.

Emigration of a colony of the leaf-cutting ant Acromyrmex heyeri Forel (Hymenoptera, Formicidae). Colony migration is a poorly studied phenomenon in leaf-cutting ants. Here we report on the emigration of a colony of the leaf-cutting ant A. heyeri in Brazil. The colony emigrated to a new location 47.4 m away from the original nest site, possibly because it had undergone considerable stress due to competitive interactions with a colony of Acromyrmex crassispinus.

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.

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.

The spatial distribution of insects is essential to perform control strategies, to improve sample techniques and to estimate economic losses. We aimed to determine the spatial distribution of nests of Acromyrmex crassispinus (Forel) in Pinus taeda plantations. The experiments were carried out in P. taeda plantations with different ages (treatments: recently-planted, three and six-year old plants). The study took place in Rio Negrinho and in Três Barras, SC. Three plots of one hectare were delimited in each treatment, and plots were divided in 64 sample units. The analysis of the dispersion index [variance/mean relationship (I), index of Morisita (Iδ) and k exponent of negative binomial distribution] showed that the majority of the samplings presented random distribution. Among the three distributions of probabilities studied: Poisson, positive binomial and negative binomial, the Poisson distribution was the best model to fit the spatial distribution of A. crassispinus nests in all samplings. The result was a random distribution in the plantings of different ages.

O objetivo deste trabalho foi avaliar a densidade e o tamanho dos formigueiros de Acromyrmex crassispinus, ao longo do ano, em plantios de Pinus taeda de diferentes idades. Os experimentos foram realizados, em Rio Negrinho e em Três Barras, SC, em talhões de P. taeda com diferentes idades (recém-plantado, três anos e seis anos de idade). Em cada tratamento, foram demarcadas três parcelas de 1 ha. Os formigueiros foram classificados em três classes de tamanho: classe I, até 30 cm de diâmetro; classe II, 31 a 60 cm; e classe III, mais que 61 cm. A densidade de formigueiros de A. crassispinus foi menor no início do desenvolvimento da floresta, praticamente duplicou nos plantios com três anos, e reduziu quando a floresta estava com seis anos. A maior densidade de formigueiros ocorreu no período de dezembro a abril. Os formigueiros aumentaram de tamanho com a idade do pínus.

The objective of this work was to evaluate the density and size of Acromyrmex crassispinus nests in Pinus taeda plantations along the year. The experiments were carried out in Rio Negrinho and Três Barras, SC, Brazil, in P. taeda plantations of different ages (recently planted and three and six years old). Three plots of one hectare were delimited in each treatment. The nests were classified according to three size classes: class I, up to 30 cm diameter; class II, 31 up to 60 cm; class III, above 61 cm. The density of A. crassispinus nests was low in recently planted areas, nearly twofold in three year-old plantations, and it reduced when the forest was six years old. The greatest nest density occurred in the period from December to April. The nests size increased along with the age of the P. taeda plantations.