Using the mark-and-release method in the estimation of adult population of sweet potato weevil, Cylas formicarius (Fabricius) in a sweet potato [Ipomoea batatas] 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 between the sexes, the males were captured with a sweep-net at 2200 and the females, by using a sweet potato tuber trap at 1400. The tubers in the trap were inside a covered plastic mesh basket for protection against rats. Weevils could go freely in and out of the basket through the mesh. The capture efficiency differed among the sweet potato cultivars used. Tubers with one third of the epidermis peeled off and left outdoors for a while were more attractive than the fresh ones. The capture efficiency of this trap decreased with the flourishing of plants. The weevils were cooled on a chilled mat (Ice-NoneR) covered with gauze so as to suppress their activity during marking. They were marked on their forewings with an oily paint-marker. Marking did not have a lethal effect upon the weevils and the loss rate of mark was negligible. PETERSEN and YAMAMURA et al. methods were used to process the mark-release data obtained in the field.