Suchergebnisse

Leaf-cutting ants manage their waste continuously to avoid risks of colony contamination. The presence of residues or their odor near foraging areas is enough for ants to stop attacking plant tissues. However, to date, no study has demonstrated an interspecific effect of nest waste on the deterrence of leaf-cutting ants. Here, we tested whether a hydroalcoholic extract of nest refuse (NR) of the leaf-cutting ants Acromyrmex balzani Emery, 1890 and Atta opaciceps Borgmeier (Hymenoptera: Formicidae, Attini) causes an interspecific deterrent effect. Field colonies of Ac. balzani (n = 30) and A. opaciceps (n = 36) were used. For each colony, we offered baits made with plastic straws covered by citrus pulp and sprayed with a hydroalcoholic solution of 20% (vol/vol) alcohol/water (Control) or an extract of 20% (vol/vol) of NR from Ac. balzani and/or A. opaciceps. Over 20-30 minutes we recorded the amount of baits removed and data were compared through survival analysis and Linear Mixed Effect (LME) model. Ants avoided collecting baits sprayed with NR resulting in less than 20% of these baits being carried to the nest versus 80% of control baits. The deterrence was both intra and interspecific, considering that the response was similar for baits from both species. Such results reinforce the premise that the presence of nest refuse alters the foraging behavior of ants and paves the way for new studies that can verify its effectiveness in reducing foliar consumption on a larger spatial scale.

The spatial distribution (SD) of organisms is a key parameter in studies of population ecology. Among the methods to describe the SD of sessile organisms, sampling by way of plots and transects are widely used. The measurement of the distance between individuals ("nearest neighbor") is a simple method that has not been employed in population studies with ants. This study aimed to evaluate the SD of ant mounds of Acromyrmex balzani (Emery, 1890), using both plot sampling and nearest neighbor methods in order to evaluate which method is more appropriate for determining SD of this species. In January 2013 we established 359 plots of 10 m2 on a fragment of grassland in Sergipe, Brazil. In the same study area 25 colonies were randomly selected and the distance of the closest neighbor colony was determined. In total, 153 ant mounds were sampled (plots) and the density was estimated in 975 × colonies ha-1. Colonies were clumped in the environment either by plot sampling (χ2 = 453.93; p < 0.05) as well as by the method of nearest neighbor (Ax= 0.67, t = -1.72, p < 0.05). The aggregation of A. balzani colonies found in this study may be due to habitat heterogeneity or relate to the strategy of colony foundation. We conclude that the use of the nearest neighbor method was as accurate as the plot sampling method, providing the same results with much lower sampling effort.

Ecological succession is a complex processes involving changes in the structure of plant community and it is an important factor determining the structure of arboreal ants assemblages, but little is known about the effects of succession on ant assemblages in regions of Tropical Dry Forests (TDFs), such as the Brazilian Caatinga. The aim of this study was to investigate the effects of ecological succession on the richness and species composition of arboreal ants in fragments of Caatinga, testing the following hypothesis: i) the richness of arboreal ants increases along a gradient of forest succession, in response to tree richness and/or density; ii) species composition of arboreal ants differs among stages of forest succession due to differences in vegetation structure in theses stages. This study was conducted in 15 plots distributed in three areas with different stages of secondary succession (early, intermediate and late). Tree density and richness were used as surrogate of vegetation structure. Ants were sampled using the technique of beating the foliage and baited pitfall traps, where five trees were sampled per plot, totaling 75 individual trees sampled. We sampled 37 species of ants, distributed in 16 genera and five subfamilies. Ant richness differed among stages of succession and seasons, with higher number of species in the late succession and rainy period, also increasing with tree richness and density. Besides, there was a distinct composition of ant species among stages of succession and seasons. Results obtained in this study reinforce the importance of using ants as environmental bioindicators, since the sensitivity to environmental variations of this group enables us to differentiate early and late successional stages of forest succession in Caatinga environment.

This study aimed to verify age polyethism occurrence in medium-sized (cephalic capsule = 2.3 ± 0.21 mm) and small-sized (cc = 1.4 ± 0.10 mm) workers from Atta sexdens (Linnaeus) colonies. Four laboratory colonies were used, and they were maintained at 25 ± 2 °C, with 75 ± 3% relative humidity and a 12-hour photoperiod. Workers from these colonies were marked after their emergence and observed throughout their lifetime to determine which tasks they performed. The number of ants performing each activity was analyzed using linear mixed-effect models (LME), considering the temporal effect and the block design (colonies). We found that fungal garden maintenance tasks were frequent for both sizes, but their occurrence decreased significantly from the ninth week. The foraging activity occurred gradually in both sizes, with stabilization in the number of workers from the fourth week onwards and declined in the last three weeks of lifespan. Waste management tasks occurred throughout life but were more frequent during the first two weeks of life, in both medium and small workers. Therefore, age polyethism may be related to all activities; however, foraging tasks presented a distinct pattern compared to tasks in the fungus garden and refuse dump, where younger ants were more frequently observed.