Abstract: The amount of pests on high trees is very difficult to be detected accurately. Thus the accuracy of prediction and forecast of the pests will be greatly affected by this reason. A vibrator which was developed by the forest Machinery Research Section of Nanjing Forestry Univesity was used to detect the amount and instars of the pine caterpillar of the overwintering generation in 1989. The height of the tested pine trees are from 5.0 to 10.2 meter and the diameter of them are from 15.0 to 25.0 centimeter. The vibrator mounted on the trunk was about 1.0 meter above the ground. After starting the vibrator, the trees were vibrated 5 times, each vibration lasted 30 seconds. and the interval between two vibrations was 5-10 minites. The average vibration fall rate of the pests was 85.4% with the highest rate up to 94.8%. The pests were easily to fell by vibration at the middle of fine days when the caterpillar were eating on the pine needles. The vibration fall rate could be used to calculate accurately the amount of the pine caterpillars on high trees. This method has many metits such as simplicity, accuracy, reliability etc. Hitting trees5.5-8.7 meters in height, and 13.3-19.7 centimeters in diameter with big stone for 10 times, the vibration fall rates are only 4.7-19.0%; and the method of calculating the larval amount by feces, is more complex and time-consuming than this method. In laboratory the frequency of the best effect was 20-30 Hz; starting instantaneous electrical current was 0.31 A; vibrating acceleration was 11.5 g.

Key words: Vibrator, Amount of pests