The seasonality of four Odonata species from mid Canterbury, South Island, New Zealand

Abstract

Odonate seasonality is determined at Isaac's Pond (43°28'S; 172°32'E) 30 m amsl and at two sites at Lake Sarah (43°03'S; 171°47'E) 579 m amsl in New Zealand. The means by which seasonality is attained and the effects that altitudinal differences have on the pattern of seasonality is examined in field and laboratory studies. Xanthocnemis zealandica (Coenagrionidae) has a two-year life cycle at Isaac's Pond, but a three-year life cycle at Lake Sarah – tb (Typha - bed site). Emergence starts earlier at Isaac's Pond, but ends by approximately the same date at all three sites. Emergence is trimodal at Isaac's Pond and bimodal at Lake Sarah. Embryonic development is direct; hatching occurs only the summer that eggs are laid. Later instar larvae cease development at about 79°C. Diapause, possibly cued by rate of change of daylength and temperature, occurs during the summer in the F-2 to F instar larvae. Austrolestes colensonis (Lestidae) has a two-year life cycle at Lake Sarah - tb. Emergence starts earlier at Isaac's Pond, but ends by approximately the same date and is bimodal at all three sites. Embryonic development usually is direct, although some delayed hatching occurs. Some eggs hatch the summer that they are laid, but others overwinter and hatch the following spring. Supplementary moulting occurs in F-2 instar larvae during the summer. Procordulia smithii (Corduliidae) has a four-year life cycle and a bimodal emergence pattern at Lake Sarah - tb. Embryonic development is direct above approximately 19°C, but greatly prolonged below this temperature; therefore, most eggs overwinter. Results from larval laboratory studies are tentative. Procordulia grayi (Corduliidae) is examined only briefly at Lake Sarah - ls (lake shore site). In general larval growth restrictions occur during the late summer that effectively prevent emergence during the autumn when successful reproduction is unlikely.