Oviposition behaviour of Sympetrum frequens (Selys) (Odonata: Libellulidae)

Abstract

Oviposition behaviour by Sympetrum frequens, a species endemic to Japan, has been observed throughout its entire breeding season, which extended for about one month after the harvest of rice. Approximately 50% of oviposition events occurred during the first week of the reproduction period. Sunny oviposition sites were preferentially selected by ovipositing pairs. The starting time of oviposition was highly correlated with the ambient temperature (Ta), the days elapsed since the beginning of the oviposition period, and the weather of the day. The mean duration of oviposition (DO) was 325.0±194.7 s in tandem oviposition (TO) and 152.5±101.8 s in oviposition of the female alone (single oviposition; SO), and DO was poorly correlated with Ta. Dip rate (DR) was constant throughout the oviposition bout; however, wing-stroke frequency (WSF) of the tandem male declined from the start of oviposition to its end. The WSF of males in TO was 39.4±2.8 Hz, significantly higher than that of tandem females (34.5±3.0 Hz, p<0.0001), but that of females in SO was as high as that of tandem males (39.7±3.7 Hz). WSF was negatively correlated with Ta. In TO the male expends more energy than the female and it controls flight direction, so for the female TO is energetically less costly than SO. Furthermore, flying-oviposition into mud is more effective than non-contact flying-oviposition as the number of eggs per dip in the former exceeds one and more eggs are deposited per time unit than in the latter.

Keywords: Odonata, dragonfly, Sympetrum frequens, oviposition, dip rate, wing-stroke frequency, number of deposited eggs

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