Conservation and utilization of natural enemies is the basic measure in biological control of agricultural pests. The enemy sub\|community in short\|term crop fields appears periodically 3 different stages that are called community reestablishment, community development and community collapse. \;Pests usually cause damage to a crop 1~2 generations after their first occurrence in the field. During that period, enemy sub\|community that is still under reestablishment is crucial to control the pests. If pests ...