Visual stimuli releasing attack of a territorial male in Sympetrum (Anisoptera: Libellulidae)

Dragonflies rely mainly on their visual sense in their interaction with the environment. Visual stimuli are significantly important in the set of isolating factors, from ecological to mechanical ones. The role of the visible pattern in male-female recognition has been investigated by many authors. There are, however, fewer experiments and fieldobservations concerning the problem ofthe territorial male recognizing its rival. (Tab. I). The distant recognition of a conspecific rival is energetically advantageous, for the male avoids useless fights with strange species. Some observers stated that territorial odonate males lack Visually released responses to a rival male were studied in territorial males of 5. sanguineum, S. vulgatum, S. flaveolum and S. pedemontanumusing a fishing-rod to present synthetic models. Film discs with the dark body centre and the concentric wing spot (if necessary) turned out to be most effective. Position and presence ofthe abdomen made nodifference. The species devoid of wing patterns (S. sanguineum, S. vulgalum, S. danae) are unable to recognize each other by appearance. Probably, they utilize other means of interspecific isolation. The species decorated with wing