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

Visually released responses to a rival male were studied in territorial males of 5. sanguineum, S. vulgatum, S. flaveolum and S. pedemontanum using 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 of the abdomen made no difference. 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 spots certainly distinguish conspecific males by the specific feature of pattern: an orange pericentral fleck in 5. flaveolum, a subapical band in S. pedemonlanum. The wing pattern shows stronger Contrast in UV than in long wave rays. S. sanguineum showed moderate aggression against patterned models, but was less selective to various models than the two patterned species. The properties of the neural perceptor detecting the configurational visual stimulus are discussed. Distant recognition of the conspecific mate by its pattern is more reliable if the latter is restricted to basal or apical flecks and bands, while thawing middle remains clear. Most odonate species with wing decoration support this rule.