Odonalulogica 19(1): 47-59 March I. 1990 A lek-like system in Lestes sponsa (Hansemann), with special reference to the diurnal changes in flight activity and mate-findingtactics (Zygoptera: Lestidae)* M. Watanabe and E. Matsunami Department of Biology, Faculty of Education, Mie University, Tsu, 514, Japan Received June 6, 1989 / Revised and Accepted September 11, 1989 Diurnal change in flight behavior was studied in Urabandai, Fukushima Pref. Japan. Marked adults were continuously followed for as long as possiblethroughout the and The day. Flight behavior was divided into cruising flight revolving flight. former the between The latter that was flight perching points. was in which a flew and landed the and damselfly around at same perching point, 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 males toward then frequency of cruising flights of mature increased noon and 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 af- ternoon. However, there was no diurnal rhythm in female flight behavior in the in A immature or the mature stage. few interferences were observed between the the floor showed immatures. Male-male interference on forest 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 females Few shoreline throughout the day, while few lone were found. 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. INTRODUCTION After emergence, adult Zygoptera, as well as Anisoptera, take several days to mature. The habitatsof damselfliesat the sexually immature stage are away from water, where they emerge and/or oviposit (CORBET, 1962). The maiden flight during the teneral stages has long been known in many damselfly species (e.g. * 8. Comparativeecological studies on Coenagrionoidea in woodlands. 48 M. Watanabe & E. Matsunami GOWER & KORMONDY, 1963; LUTZ, 1968; CORBET, 1980). Although many works have been conducted on mating behavior (ALCOCK, 1982; UTZER1 et al., 1983; FINCKE, 1985), no lek system in Zygoptera has been reported. Damselflies of the genus Lestes, characterized by the emerald color of their bodies, have a relatively long sexually immature period (SAWCHYN & GILLOTT, 1974a, 1974b; UEDA & IWASAK.I, 1982; CORDERO, 1988). In Urabandai, northern Honshu, L. sponsa emerges in late June and begins to in late oviposit July, suggesting that the sexually immature period lasts over a month (WATANABE et al., 1986). WATANABE et al. out that (1986) pointed some Zygoptera (L. sponsa , L. temporalis, Platycnemis echigoana) tend to stay throughout their lifetime in the forest near where and The first water, they emerge oviposit. two are non-terri- torial and the third is territorial a damselfly. In these two Lestes species, the habitats of the sexually immatureand mature individualsare thesame. The forest floor is also known to be the site for and is site which mating, a does not holdany for damselfies. resource the CAMPANELLA & WOLF (1974) pointed out that such a kind mating system was a of lek. Although considerable evidence on the behavior and the of ecology mature L. sponsa is available (e.g. UEDA, 1978), little attention has been given to the diurnal change in flight activity throughout the lifespan. In this paper, the diurnal flight activity pattern at the sexually immature is with that of individuals. stage compared mature A lek-like system in L. sponsa relative to the mate-finding tactics is also examined. MATERIAL AND METHODS Field data were collected from late June to mid August (1984, 1985, 1987) in Urabandai. The study area has already been described OHSAWA in detail (e.g. & WATANABE, 1984; OHSAWA et al.. 1985). Among eight of forests main and study plots near ponds, one plot (K-ike) a subsidiary one chosen for the (N-ike) were observation of flight behavior ofsexually immature and mature adults of L. Both where dominant the sponsa. were secondary forests, the species are larch. Larix leptolepis,in the former, and the Japanese red pine, Pinus densiflora, with Rhus trichocarpa in the latter. The sizes of the ponds were similar (about 200 m long). Before the beginning each observation on flight behavior, we intensively patrolled study plots for two mark adults. Damselflies days to were captured in a net, and marked individuallyon their hind with fell With little it wings a pen. a practice, was easy to read such marks individually duringthe investigation. The degree of wing wear and the color of the abdomen were recorded in order to WATANABE obtain information on ageing (cf. & ADACHI. 1987a, 1987b). Marked adults were continuously followed for as long as possible throughoutthe day: from the of in onset the flightactivity the morningto the time ofroosting in theevening, monitoringthe time spent on various flight activities. Observations from were made 6:00 to 18:00 for a total of7 days; 3 and 4 for days immature and mature adults, respectively. The numbers observed continuously during more than 5 min were 20 and 10 in immature males and females, 90 and 36 in mature males and females, respectively. The identities of individuals with single perching, flying, fighting conspecifics, preying upon small the the insects, etc., at perching point on forest floor were recorded by direct observations. Such Lesies Lek-like system in sponsa 49 similar barbarus behavioral patterns were basically to those identified in L. and L. virens (UTZE RI et al.. 1987). Calopteryx cornelia (HIGASHI & UHDA. 1982), P. echigoana (OHSAWA & WA- TANABE. 1984) and Hetaerina macropus (EBERHARD, 1986). The distance and the height of each also recorded. behavior divided accordance with the flight were Flight was into two types in flight route: cruising flight and revolving flight. The former was the movement from oneperch to another. The latter was the flight+landing of a damselflyreturning to the same perch. Revolving subdivided into and the flights were patrolling flight encounter flight. Of flight behaviors, a flight without the Encounter any reason(as seen by observers) was regarded as a patrollingflight. flight is caused by interference from other insects comingnear the perch. Since damselflies ate prey at the original perch after catching it, and since they rested at the perch after their attack on conspecific all intruders, encounter flights were included in revolving flights. the of To obtain further information on diurnal change reproductive behaviour, the distribution the line two-hour whole in main plot was mappedalong a survey at intervals for a dayon the 8th and 9th August. 1987. following the recording. The survey line was divided into 35 sections which included the forest floor and the shoreline (total 823 m2 ): 23 sections (24.6±I8.5 m 2) were in the 2 forest floor and 12 (2I.4±3.7 m ) were in the shoreline (SE).They occupied 16% of the area ofthe All the main plot. of sections were carefully searched for perching, copulating, and ovipositing All individuals. The sex, number, and age were noted. measurements are given as mean +SE. RESULTS CRUISING FLIGHT The adults captured were classified into two broad categories; sexually im- mature and mature. In each sampling period, the adult population was rather the min. for Fig. 1. Changes in frequency of cruisingflights per 5 sexually immature (left)and mature (right) adults of L. sponsa. Circles and triangles show males and females, respectively. 50 M. Watanabe & E. Matsunami with because of the considerable of homogeneous respect to age synchronization The total of in main emergence. number L. sponsa marked the plot, K-ike, was about 300 males and 150 females in each year. The duration of in most flights was less than 1 second, as the case of P. echigoana (WATANABE et al., 1987). Cruising flight was the slowest and its duration was the longest, but did not exceed 3 seconds. immature females Both males and tended to stay on the forest floor. They of which perched mainly on the stems Sasa paniculata, was dominant at K-ike. A shift of perch took place at relatively constant intervals (0.4 times per 5 min. approx.) throughout the day, except forthe females in the evening (Fig. 1). There was no significant difference between the sexes in the frequency of the cruising flights per hour except at 17:00 h (F-test). females after of Mature were observed 9:00 h. Thedaily trend cruising flights in mature females was similar to that of immature ones. However, with mature males the frequency of cruising flights increased in the morning after 6:00 h, remained at a higher level than that of the immature males around noon (2.5 times min. per 5 approx.), and then gradually decreased. During the early morning in of similar particular, the frequency the males was to that of the females. The daily pattern of the cruising flights in mature males seemed to be related tothatof reproductive behavior. At the immature stage, the length of cruising flights, i.e. the distance between successive the in the in two perches, was longest evening both males(F=6.852, P < 0.01) and females (F = 6.203, P < 0.01) (Tab. I). They moved further in the evening, and some left the forest floor. They may have been seeking a roosting point rather than the so-called perching point in the evening. Some of them rose floor remained floor. from the forest to the tree tops, but others on the Table 1 Changes in the length (I) of cruising flight of sexually immature and mature adults of L.