USING THE MARK-AND-RELEASE METHOD IN THE ESTIMATION OF ADULT-POPULATION OF SWEET-POTATO WEEVIL, CYLAS-FORMICARIUS (FABRICIUS) IN A SWEET-POTATO FIELD

The object of this study was to develop a procedure for estimating the adult population of sweet potato weevil, Cylas formicarius (FABRICIUS ), distributed in a relatively small field, by using the mark-release method. Considering the difference of the diurnal activity rhythms bet ween the sexes, the males were captured with a sweep-net at 2200 and t he females, by using a sweet potato tuber trap at 1400. The tubers in the trap were inside a covered plastic mesh basket for protection agai nst rats. Weevils could go freely in and out of the basket through the mesh. The capture efficiency differed among the sweet potato cultivar s used. Tubers with one third of the epidermis peeled off and left out doors for a while were more attractive than the fresh ones. The captur e efficiency of this trap decreased with the flourishing of plants. Th e weevils were cooled on a chilled mat (Ice-None(R)) covered with gauz e so as to suppress their activity during marking. They were marked on their forewings with an oily paint-marker. Marking did not have a let hal effect upon the weevils and the loss rate of mark was negligible. PETERSEN and YAMAMURA et al. methods were used to process the mark-rel ease data obtained in the field.