Prediction of Successful Eradication of the Oriental Fruit Fly, Dacus dorsalis HENDEL (Diptera: Tephritidae) Using Spatial Distribution Indices

Abstract

During the course of an eradication program by the application of the male annihilation method (MA) for the control of the oriental fruit fly, Dacus dorsalis HENDEL, on the Miyako Islands and the Yaeyama Islands, Okinawa, Japan, the values of the index of contagiousness, I_δ, and IWAO'S ‘density-contagiousness coefficient’, β, were calculated from the frequency distribution of the numbers of flies caught in traps distributed in the target areas. The values of both I_δ and β during the period of MA implementation were slightly higher than or nearly equal to those in the pre-control period in such places as Ishigaki, Yonaguni and Tarama Islands, where MA has been successfully implemented throughout. In contrast, the corresponding values during the period of MA implementation apparently increased immediately after the initiation of MA application on Iriomote Island and in Ueno Village on Miyako Island, where MA was only partly effective initially, and the eradication had not been achieved until the dosage was increased and the method of application of methyleugenol was revised. In the latter case, it was suggested that the effect of MA varied among the local patches in the total population of the fly. Therefore, successful eradication with MA can be predicted in the early phase of MA implementation by observing the changes in the contagiousness parameters based on the frequency distribution of the number of flies trapped. These results suggest that not only temporal changes but also the spatial distribution pattern of the target insect population must be analysed to evaluate the effects of methods of eradication.