Habitat selection and oviposition site recognition by the dragonfly Aeshna juncea (L.): an experimental approach in natural habitats (Anisoptera: Aeshnidae)

The behaviour of 6 and $ individuals was studied at natural and artificial breeding stites. In order to detect the stimuli by which the adult insects recognize their larval habitats dummies varying in size (0.02-8 m2) and material (black plastic foil, black and white cotton cloth, tulle) were set up in the vicinity of or apart from natural pools. In multiple choice experiments black plastic foil proved highly attractive to both sexes. They exhibited the complete repertoire of behavioural elements which belong to reproduction including site defence and oviposition. Two behavioural elements were analysed quantitatively, that is the number of arrivals and the duration of stay at dummy sites and at natural pools. The males frequented large foil areas more often than small ones and they stayed over them longer. Glass splinters feigning the sparkling light reflections present at natural breeding sites did not enhance the attractiveness of a dummy. In full sunshine a natural pool was preferred to a dummy of about the same size. However, the attractiveness of these sites was reversed when the sun became covered by a cloud. From the results of the choice experiments it may be concluded that the most effective stimuli by which the adult dragonflies recognize suitable oviposition sites comprise a coarse pattern of reflecting areas on dark background. They prefer large areas to small ones. Non-shining black areas have little effect and white ones have none or even repel insects. Sparkling light reflection patterns alone are obviously poor cues, as they evoke only weak responses or none at all.