Dispersal, feeding and parasitism of adult stoneflies (Plecoptera) at a New Zealand forest stream

Abstract

The temporal occurrence and dispersal of stoneflies were investigated at a forest stream in the South Island, New Zealand. Although 12 species were taken in Malaise traps, only Spaniocerca zelandica and Cristaperla fimbria (Notonemouridae) were abundant. Adults of S. zelandica were present throughout the year and a wide range of different-sized nymphs, including very small individuals, was also found in all months. In contrast, the emergence period of C. fimbria was limited to about four months in summer and as nymphs are mainly hyporheic, few were taken in Surber samples. Malaise trapping on a 16 m long transect away from the stream and with more distantly located traps in forest and grassland resulted in a very high proportion of males and females of both species being caught within 1 m of the stream edge. Captured females of both species included immature, gravid, and spent individuals. Males and females of both species had almost identical diets dominated by sooty mould fungi, fungal spores, pollen and fine particulate organic matter. High proportions of them were also infected by the encysted larvae of a gordian worm (Nematomorpha) and may be important vectors in its life cycle.