Notes on tandem oviposition and other aspects of reproductive behaviour in Sympetrum vicinum (Hagen) (Anisoptera: Libellulidae)

Tandem oviposition (contact guarding) in low-density populations was observed at a small pond in New York State. Oviposition generally occurred between 1200-1430, during which time pairs appeared at the water already in tandem. Searches of the surroundings failed to reveal aggregations of tandem pairs; hence pairs may have flown immediately to the water or may have come from greater distances. Many arriving tandems performed dipping movements over potential oviposition sites along the shoreline. This behaviour resembled oviposition, was often followed by copulation, and may have functioned to show the 9 oviposition sites and thereby induce mating. During tandem oviposition, the c? alternately dipped the 9’s abdomen into the water and struck it against the pond bank or other surface; such actions probably deposited eggs both in the water and on mud or shore vegetation. As many as 10 pairs occasionally oviposited 5-10 cm from one another at the same site. Occasional lone 6 6 were present near oviposition areas, but rarely disrupted tandem pairs; no takeovers or rematings of ovipositing 9 9 were recorded. Guarders stayed in tandem for the duration of oviposition and never switched to non-contact guarding. The adaptive significance of contact guarding in S. vicinum is discussed with reference to other members of the genus.