Dynamics of the restoration of physical trails in the grass-cutting ant Atta capiguara (Hymenoptera, Formicidae)

ABSTRACT Dynamics of the restoration of physical trails in the grass-cutting ant Atta capiguara. Leaf-cutting ants of the genus Atta build long physical trails by cutting the vegetation growing on the soil surface and removing the small objects they find across their path. Little is known on the dynamics of trail construction in these ants. How much time do they need to build a trail? To answer this question we selected six trails belonging to two different nests of A. capiguara and removed on each trail a block of soil of 20 cm × 15 cm that included a portion of the physical trail. This block was then replaced by a new block of the same size that was removed in the pasture near the trail and that was uniformly covered by the same type of vegetation as that found on the block of soil that was removed. The time required to restore the trail was then evaluated by the length of the grass blades found along the former location of the trail. The results show that ants rapidly restore the portion of the physical trail that was interrupted, which suggests that they could also do the same after their trails have been recolonized by the vegetation.

Interações entre as modalidades visual e olfativa na orientação espacial de operárias da espécie formica rufa (Hymenoptera; Formicidae) / Interaction between visual and olfactory stimulus modalities in the spatial orientation of formica rufa worker ants (Hymenoptera; Formicidae)

Operárias de Formica rufa utilizam estimulação química e visual para se orientar espacialmente. Objetivou-se verificar a contribuição dessas modalidades sensoriais em situações experimentais nas quais um tipo de estimulação pertinente era retirado ou modifi cado. Na primeira experiência, que serviu de comparação para as próximas, as formigas foram liberadas em um ambiente inalterado com relação à situação familiar. Na segunda experiência, uma cortina foi colocada entre o dispositivo experimental e a estimulação visual da sala. Na terceira, todo o dispositivo sofreu rotação de 180°. Cada situação dessas foi seguida por uma semelhante em todos os parâmetros, exceto pelo da pista química que foi interrompida em determinado ponto. Concluiu-se que as operárias puderam se orientar corretamente utilizando apenas uma das modalidades; que não utilizaram informações visuais situadas no teto e que aprenderam a se deslocar seguindo orientação contextualizada: em direção ao alimento ou em direção ao ninho.

Formica rufa worker ants use chemical and visual stimulation for spatial orientation. This work aimed to verify the contribution of these sensorial modalities in experimental situations in which one kind of pertinent stimulation was removed or modified. In the first experience, which served as comparison to the next ones, the ants were released in an unchanged environment concerning to the familiar situation. In the second experience, a curtain was placed between the experimental apparatus and the visual stimulation in the room. In the third experience, the whole apparatus was rotated 180 degrees. Each of these experiences was followed by one similar experience with respect to all parameters, except the chemical clue, which was discontinued in a certain point. We conclude that (1) the worker ants could orientate correctly using only one of the sensorial modalities; (2) they did not use visual information from the ceiling, and (3) they have learned to move using contextualized orientation: towards food or towards the nest.