Nocturnal behaviour and the antennal sensory receptors of Zelandopsyche ingens Tillyard (Trichoptera: Oeconesidae), a stream-inhabiting caddisfly

Abstract

ABSTRACT Females of many species of Trichoptera (caddisflies) use pheromones to attract males prior to mating. A diverse array of chemosensory sensilla present on the antennae of both males and females are likely to mediate communication between the sexes. Zelandopsyche ingens Tillyard is a large oeconesid caddisfly, which inhabits small forest streams in the South Island of New Zealand. At night, males of Z. ingens were found standing on the tops of large stones projecting from the stream bed and waving their antennae up and down. This behaviour is thought to be associated with the detection of chemosensory signals from con-specific females. Meanwhile, females occupied various substrata on the stream bank and within the channel. Bi-directional sticky traps placed immediately above the stream collected large numbers of low-flying males, particularly on their downstream sides suggesting many may have been moving upstream in response to pheromonal cues. Some captured females had laid eggs on the traps indicating they were undertaking oviposition flights. Sensilla on the antennae of both sexes were predominantly forward-directed long grooved trichoids overlying numerous short stellate pseudoplacoids of two morphological forms that have not been described before.