Marking of nest entrance vicinity in the ant Pheidole pallidula (Formicidae, Myrmicinae)

The present work demonstrates the marking of the immediate vicinity of the nest entrances in the ant Pheidole pallidula. These areas attract and arrest nestmates but deter alien ants; they are the nearest approached by nestmates, which ants walk also the more in their midst. On such areas, nestmates are quieter when alone and more aggressive in the close presence of an intruder than on virgin areas, whereas alien ants are more excited and less inclined to attack. The vicinity of the nest entrances is thus perceived as being territorially marked, according to Hölldobler and Wilson's definition (1990), and the different agonistic behaviour of intruder and resident workers on such a marked area reflects what is known as a Bourgeois strategy. The colony-specific marking of the nest entrance vicinity is established slowly and is rather long-lasting: it becomes obvious after 12 h and persists for nearly the same time. The marking is produced by non-recruited minor workers leaving their nest and walking around the entrance before going any further. It is not due to the deposit of faecal material, nor of secretions from the poison or the Dufour glands. The legs, fragments of legs, thorax, third segment of thorax and metapleural glands of minor workers all present an ethological activity identical to that of a territorially marked area. An acetone extract of minors' metapleural glands is active. Therefore, it appears that the minors mark the immediate vicinity of the nest entrances by depositing by their legs the metapleural gland contents.