Ecological role of Zelandopsyche ingens (Trichoptera: Oeconesidae) in a beech forest system ecosystem

Abstract

An ecological study of the trichopteran Z. ingens was made in a small stream flowing through mountain beech forest in the South Island of New Zealand. Larvae were present throughout the year, many being in early instars in summer and early autumn whereas the final instar was predominant from May to January inclusive. Pupation and emergence occurred in summer. The size of the larval population in a 93-m section of stream was estimated on three occasions using mesh colonization trays. Densities ranged from 61 to 97 larvae/m². Over 1500 larvae belonging to the final three instars, or about 25% of the estimated population in the section, were trapped drifting out of the section in an 8-month period. Larvae fed mainly on dead beech leaves which were assimilated with an efficiency of 8-24 %. Results of [¹⁴C]glucose labelling experiments indicated that much of the microflora present on dead leaves was assimilated by larvae. Fine particle production rates (approximately equal to egestion rates) were measured in laboratory feeding experiments at three temperatures and combined with field data on the life history and population size to estimate annual litter breakdown. It was estimated that approximately 11 % of the beech leaves and twigs entering the experimental stream section were broken down by Z. ingens.