Determining numbers of active carabid beetles per unit area from pitfall-trap data

Movement of Pterostichus melanarius (Illiger) (Coleoptera: Carabidae) was studied in the laboratory, and a simulation model developed. The model was calibrated and validated using mark-release-recapture within a grid of pitfall traps in a commercial raspberry field. Rate of movement increased linearly with both temperature and starvation. The temperature threshold for movement, pooling all starvation levels was 3.8 °C ± 0.78 (s.e.). When beetles were released at various distances from a trap in the simulation model, the probability of capture during one day was about 0.13 at a release distance of 10 cm and fell rapidly with distance and temperature. At 5, 10, 15, and 20 °C, the maximum radius sampled by a trap in one day was about 8, 17, 24, and 29 m, respectively. Density was linearly related to catch, but the slope of the line and the variance of the density estimate increased rapidly at lower temperatures. Equations for determining density per m² (±s.d.) were developed from the model, incorporating temperature, number of beetles caught per trap, and number of traps.