Balancing sampling effort in pitfall trapping of carabid beetles

Samples of carabids were collected from two study areas in southern Finnish coniferous forest using continuous pitfall trapping throughout the breeding season. These were compared with samples from combinations of early and late season sampling periods (5+5, 10+10 or 14+14 days in each combination). The same species were abundart in both the smaller samples from combinations of periods and in the whole season samples. There was considerable variation in the total catch of carabids among the 10-day samples (5+5 days) which mainly reflected fluctuation in catch of the abundant species in the early season. About 42% of the total number of species was caught in every 10-day sample, 52% in every 20-day sample, and 61% and 77% in every 28-day sample. Most species not caught during the shorter trapping periods were scarce in the whole season sample (<10 individuals). We suggest that samples obtained by trapping periods of 20 days or more were similar enough to the whole season sample to be used in several types of ecoiogical studies