Mariane Nickele

O controle químico através de iscas formicidas é o método de combate às formigas cortadeiras mais utilizado pelas empresas florestais. No entanto, o combate às formigas cortadeiras tem sido estabelecido de maneira padronizada na maioria dos plantios florestais, não levando em consideração as particularidades de cada região. O objetivo desse trabalho é apresentar algumas recomendações para o controle de formigas cortadeiras em plantios de Eucalyptus e Pinus, levando em consideração os gêneros de formigas cortadeiras e as diferentes formas de manejo florestal adotadas pelas empresas de base florestal, visando a redução do uso de iscas formicidas, sem que haja prejuízos aos produtores.

Leaf-cutting ants are well-known insects due to their remarkable activity as
herbivores and the considerable economic damage they cause to many crops.
The identification of season and time of day when leaf-cutting ants are most
active is an important tool, not just to understand the foraging ecology of these
ants, but also to optimize their control in plantation areas where they are pests.
Thus, the aims of this study are to evaluate the daily foraging activity of leafcutting
ant species of the genus Acromyrmex, which occur in forest plantations
in Southern Brazil. Foraging activity of Acromyrmex crassispinus (Forel) and
Acromyrmex subterraneus subterraneus (Forel) were correlated with weather
conditions, and it was more intense during spring and summer. Workers that
forage at night are significantly heavier than workers that forage during the day.
This study showed that A. crassispinus and A. subterraneus subterraneus did
not forage at temperatures below 10-11°C. Then, the use of granulated baits to
control these leaf-cutting ants species where they are pests should be done just
under favorable conditions of temperature for Acromyrmex foraging activity (over
12°C), to ensure maximum collection of baits by ants and the least left-over baits.

This work aimed to study the population dynamics of Acromyrmex crassispinus (Forel) in
Pinus taeda L. plantations, evaluating the density and spatial distribution of nests over
time, inferring about the period of the first nuptial flight of A. crassispinus colonies, and
evaluating the levels of attack of this leaf-cutting ant on P. taeda plants. Assessments
were performed monthly in the first year after planting, every three months until the
third year and every six months until the plantation was six years old. The presence
of nests was observed only after 15 months after planting. The nest density gradually
increased until the planting completed 30 months, and decreased when the forest canopy
began to close (after 54 months). Spatial distribution of A. crassispinus nests was random.
Probably, the first nuptial flight of an A. crassispinus colony occurred after the third
year of the colony foundation. Pinus taeda plants were not attacked by A. crassispinus
throughout the evaluation period. Then, when dealing with a replanting area of Pinus
plantation, where the previous forest has not been subject to pruning nor thinning,
the problem with A. crassispinus is almost null if the clearcutting and the new planting
occur during the winter. In this case, leaf-cutting ants control can be alleviated and it
is not necessary to carry out systematic control of ants where A. crassispinus is the
predominant leaf cutting ant species. Acromyrmex crassispinus control should be done
only if nests are located or if attacked plants by ants are detected.

The complex social organization of leaf cutter ants is closely linked with intricate patterns of division of labor in the worker force. For instance, foraging might involve division of labor between cutters and carriers, as well as task partitioning during leaf transport. However, little is known about division of labor during foraging in Acromyrmex, particularly under field conditions. The goal of the present study is to investigate the behavior of Acromyrmex leaf-cutting ants on trails of different lengths in order to elucidate the effect of foraging distance on the occurrence of transport chains under field and laboratory conditions, and to discuss the hypotheses to explain the occurrence of transport chains. In Acromyrmex crassispinus (FOREL, 1909) and Acromyrmex subterraneus subterraneus (FOREL, 1893), cutting and carrying of fragments were clearly separated activities performed by distinct worker groups differing in body size. In addition, the behavior of foragers of both species differed significantly according to variation in trail distances. On short trails (1 m), cutters frequently transported the fragments directly to the nest, whereas on long trails (more than 10 m), most cutters transferred the fragments to other workers. Transport chains happened more frequently when workers harvested plants far from the nest. These results demonstrate that Acromyrmex species display both division of labor between cutters and carriers, and task partitioning during leaf transport, with trail lengths showing marked effects on the likelihood of sequential transport. Furthermore, the results of this study provide support for the hypothesis that the be-havioral response of transferring fragments in Acromyrmex species would have been selected for because of its positive effect on the information flow between workers.

Resumo: As formigas cortadeiras destacam-se como as principais pragas de plantios de Pinus e Eucalyptus. Na Região Sul do Brasil, por haver poucas informações sobre o comportamento das espécies de formigas cortadeiras, até pouco tempo atrás o combate era realizado de maneira padronizada, não levando em consideração as particularida-des de cada região. Assim, o objetivo desse trabalho é apresentar os resultados das pesquisas sobre o manejo de Acromyrmex em plantios de pinus e eucalipto na Região Sul do Brasil, realizadas pela Embrapa Florestas, em parceria com a Epagri, UFPR e Funcema, visando a otimização do controle dessas formigas. Foram encontradas 7 espécies de Acromyrmex associadas aos plantios fl orestais localizados na Região Sul do Brasil, sendo que Acromyrmex crassispinus é a mais frequente. A densidade de ninhos de A. crassispinus aumenta gradualmente ao longo do tempo em plantios de pinus e eucalipto, mas diminui drasticamente quando o dossel da fl oresta se fecha. Os ataques de Acromyrmex em plantas de pinus e eucalipto ocorrem principalmente nos primeiros meses após o plantio, e é infl uenciado pelo manejo de plantas daninhas em plantios de pinus. Assim, o combate às formigas cortadeiras do gênero Acromyrmex em plantios de pinus e eucalipto localizados na Região Sul do Brasil, depende da espécie plantada e do manejo fl orestal. Mas, de maneira geral, deve ser direcionado para o período mais vulnerável dos plantios, que são os primeiros meses de idade do plantio, o que pode representar uma grande economia de insumos e mão-de-obra.