Abstract
A total of 22 wooden frames (30×30×20cm) covered with cheese wire net were set up in a fallow paddy field and were introduced 20 mature nymphs of Nephotettix cincticeps each either with or without a subadult female of Lycosa pseudoannulata. The number of leafhoppers disappeared was counted weekly in the frame from late January to late March. The number of leafhoppers was kept at 20 per frame by adding artificially on each census.
In terms of the number of samples and biomass, it was thought the effective predators were mostly consisted of L. pseudoannulata, micryphantid spiders, staphylinids and carabids. Concerning 4 species of predators which represent each predator group, i.e. L. pseudoannulata, Oedothorax insecticeps, Paederus fuscipes and Pterostichus longinquus, the numbers of mature nymphs of N. cincticeps attacked per day were examined at different temperatures: 5, 10, 15, 20 and 25°C. The calculated predation zero points were respectively 5.2, 1.4, 8.6 and 4.0°C. Above 10°C L. pseudoannulata was definitely superior to others in attacking the prey. The daily mean temperatures at 2cm above the ground surface in the experimental field was higher than that measured at 1.2m by about 7°C and rarely recorded below the predation zero point of L. pseudoannulata suggesting the continuous predation on N. cincticeps throughout the winter. The mean total number of leafhoppers disappeared in the frames was 19.5 with the presence of L. pseudoannulata as against 3.7 without it.
As a result it was suggested L. pseudoannulata plays an important role as a mortality factor of N. cincticeps even in winter. Based on the relationship between the number of N. cincticeps disappeared and the predator days (No. predators×No. days present) of L. pseudoannulata, it was shown that N. cincticeps may be decreased to one-half during the winter in the presence of L. pseudoannulata at a density of 5 individuals per m2 early in the overwintering season.
