Eficiência de barreiras físicas no controle de Acromyrmex Mayr, 1865 (Hymenoptera: Formicidae)

Abstract

The leaf-cutting ants (Acromyrmex spp.) are important agricultural pests and their populations may be controlled by different methods. Among them, the use of physical barriers that prevent the access of the leaf-cutting ants to plants, mainly to their aerial part. However, although it is an old technique, few studies show the efficiency of these barriers on the control of these pests. The present work aimed to evaluate the efficiency of conical and cylindrical craft physical barrier barriers and a physical barrier available in the Brazilian market on the control of Acromyrmex in the field conditions, on the control of Acromyrmex, as well to evaluate foraging behavior of these ants in the presence of these barriers. Six experiments were conducted from February to March, 2001 on a home garden located in Petropolis in Rio de Janeiro state. In the first experiment orange peels as attractant baits fixed at the top of the eucalyptus branches constituted three treatments: baits protected by conical craft barriers of 5,4 cm or 10,8 cm of generatrix and baits without protection of barriers, which constituted the control. The second experiment was installed on a root of an epiphyte plant, in which similar cones to experiment 1 were placed. In the third, fourth and fifth experiments cabbage seedlings, a rose plant and a star fruit tree were used, respectively, in which conical and cylindrical craft physical barriers were placed as well as a cylindrical trade barrier. In the sixth experiment seven citrus seedlings were used. Initially, two citrus seedlings were protected by the conical craft barriers, being one seedling with the big cone and another with the small cone, and the others were left without protection in order to be attacked by the ants and after to be protected with the barrier only when they begin to be attacked. Two species of leaf-cutting ant were identified: Acromyrmex niger (F. Smith) and Acromyrmex disciger (Mayr). The conical craft physical barrier was able to avoid the access of the leaf-cutting ants to the food resource, but the cylindrical barrier is more efficient than the two models of the craft physical barriers due to present the bend at the edge that difficult the passage of ants carrying fragments of leaves. In highly attractive plants such as rose, already attacked by ants, the efficiency of the physical barrier may be lost. The conical craft barrier with generatrix of 10.8 cm contains the ants the attack on plants, but depends on the time of application (before or after the infestation by ants) and the type of plant (attractive or not). In more attractive plants as rose and start fruit, the cones were only effective when placed on plants not infested by the ants. However, the citrus plants were protected with cones even after they were being attacked by the ants.