PROBLEM TO BE SOLVED: To provide a method to improve an initial fixing ratio of a natural enemy after discharging without increasing cost and labor.SOLUTION: In a universe consisting of populations belonging to Class Insecta or Class Arachnida as natural enemies for biological controls, a local concentrated search type natural enemy with high fixity is chosen by extracting individuals of low-order 35% of walking and/or flying active mass during some period of time.