A lek-like system in Lestes sponsa (Hansemann), with special reference to the diurnal changes in flight activity and mate-finding tactics (Zygoptera: Lestidae)

Diurnal change in flight behavior was studied in Urabandai, Fukushima Pref. Japan. Marked adults were continuously followed for as long as possible throughout the day. Flight behavior was divided into cruising flight and revolving flight. The former was the flight between perching points. The latter was that in which a damselfly flew around and landed at the same perching point, and was subdivided into patrolling flights and encounter flights, which included feeding and interference. Both males and females, when sexually immature, stayed on the forest floor. The frequency of cruising flights of mature males increased toward noon and then remained at rather high levels. The frequency of revolving flights in mature males increased in the morning, attained a peak around noon, and decreased in the afternoon. However, there was no diurnal rhythm in female flight behavior in the immature or in the mature stage. A few interferences were observed between the immatures. Male-male interference on the forest floor showed a diurnal rhythm in accordance with the mating behavior of mature males. Solitary males interfered in copulation there. On the other hand, solitary males were also observed on the shoreline throughout the day, while few lone females were found. Few of them, arriving from the forest, interfered in the oviposition in tandem. A lek-like system in L. sponsa is discussed in view of these observations.