SEASONALITY, SEX-RATIOS AND ARRIVAL PATTERN OF SOME NEW-ZEALAND CADDIS (TRICHOPTERA) TO LIGHT-TRAPS

We report the results of three independent light-trapping studies of c addis (Trichoptera) at three widely-separated stream-side sites in New Zealand. A total of 66 caddis species in 10 families was recorded, as follows: 33 from site K (Kawarau Gorge) in 1990-91, 28 from site T (T uritea Stream) in 1986-87 and 45 from site W (Waitakere Stream/Cascade Stream) in 1967-68. Many of the species were captured in sufficient n umbers to estimate their adult flight season. The results show that so me species in the families Hydrobiosidae, Hydroptilidae and perhaps al so Philopotamidae and Chathamiidae are present as adults during every month of the year. Species captured from 7 other families appeared to have a mid-winter break with no active adults present. For some specie s there is a marked change in the sex ratio through the flight season from predominantly males early in the season to predominantly females at the end. For four common species at one site, the arrival pattern a t the light trap was unimodal. It was highest shortly after sunset for three of the species; the fourth showed a peak in arrival rate four h ours after sunset. Numbers of insects captured were strongly dependent on air temperature.