REPRODUCTION BEHAVIOUR DURING HEAVY RAINFALL OF OXYSTIGMA WILLIAMSONI GEIJSKES (ZYGOPTERA: MEGAPODAGRIONIDAE) IN SURINAM. 

During a stay in Surinam (1 February-15 April, 1989) I conducted research on a running water system in the tropical rain forest, 100 km SW of Paramaribo (5o48' N., 55o85' W.). I visited the Siparikreek and the Tibitiriver for 14 days. Although it was supposed to be “the short dry season” from February to April, it rained in the afternoon nearly every day. On 18 February I observed dragonflies near the Siparikreek, 50 m downstream from the bridge which connects Zanderij and Witagron. Most Odonata disappeared as heavy rainfall started around 14.25 h. A few minutes later I noticed a Zygoptera flying low over the water surface, with his abdomen slightly pointed down, at an angle of about 10 degrees. It turned out to be a patrolling male of Oxystigma williamsoni Geijskes, 1976. Other males were perching on the shore vegetation at a height of 5-10 cm. Soon after a female was seen ovipositing alone in a floating leaf. The male grasped her and they flew in tandem into the forest. Between 14.44 and 14.48 h. four couples arrived at the site where the first female had been seen ovipositing. During oviposition, the pairs maintained the tandem position. When rainfall decreased around 14.55, single patrolling males disappeared. But when a few minutes later the rain intensified once more, they were seen again flying low over the water or perching on shore vegetation. At 15.00 I had to leave the site.On 21 February I revisited this location. During a short, light rain shower around 14.00, no reproductive activity was noticed. At 18.00, however, heavy rain started and soon after this moment a male Oxystigma williamsoni was noticed perching close to the site where the ovipositing tandems had been seen a few days earlier. At 18.20 a pair started ovipositing in tandem with only the female totally submerged. Close to them a male was perching. This place, the only place where reproductive behaviour was seen, was a small clearing along the creek with some marsh plants growing in the water. Ovipositing was seen only at the downstream pointed part, where only three leaves were used for oviposition, even though more suitable substrate seemed to be present. Eggs (0.9x0.2 mm) were perpendicularly inserted in soft floating leaves (maximum 30 eggs per square cm). An illustration of a leaf with eggs is given by D.C. GEIJSKES (1976, Odonatologica 5(3):213-230). Non-reproductive activity was observed in the forest near the creek, where solitary males were perching on twigs on a height of 0.5 m from 9.45 to 17.40. A juvenile specimen was found on 29 March near a small brook upstream of the bridge. These observations allow the following tentative statements. 1) Reproductive activity of O. williamsoni probably takes place only during heavy rainfall. With the description of this species GEIJSKES (1976, op. cit.) the author includes some field notes in which he writes about the curious phenomenon of oviposition during heavy rainfall. My observations suggest that all reproductive activity takes place during heavy rainfall, the first case to be reposted for a zygopteran. This kind of behaviour has only been described before for two anisopteran species (Malgassophlebia: Libellulidae, Tetrathemistinae) from the tropical rainforest in Makakou, Gabon (J. LEGRAND, 1979, Rev.fr.Ent.(N.S.) 1: 3-12; J. LEGRAND, 1986, in Current topics in dragonfly biology Vol.2, P.S. CORBET (ed.), p.17-18. Soc.int. Odonatol., Bilthoven). - 2) Mating time seems to be about 15 minutes. - 3) All specimen of the species were seen near a small creek and near the sandy part of the Siparikreek - which both will dry up during normal dry seasons - not farther downstream on the sluggish part of the Siparikreek or on the Tibitiriver. GEIJSKES (1976, op. cit.) refers to the species as common in Surinam near creeks. M.T. Wasscher, Minstraat 15 bis, 3582 CA Utrecht, The Netherlands

See   for a key in Dutch for both Oxystigma species occurring in Suriname.