ヤノネキイロコバチ放飼園におけるヤノネカイガラムシ寄生果率の年変化

抄録

Annual changes in adult female density and fruit infestation rate of the arrowhead scale, Unaspis yanonensis, were examined from 1983 to 1988 at a citrus orchard where the parasitoid, Aphytis yvanonensis, was released in 1982. After the release the scale density and the fruit infestation rate decreased. However, the fruit infestation rate exceeded 0.1. A positive relationship between the scale density and the fruit infestation rate was observed. This relationship suggests that we need to suppress the density of U. yanonensis females below 0. 013 per leaf in November so as to maintain the fruit infestation rate under 0. 05. It seems difficult for A. yanonensis to keep the pest population at such a low level. Most of the scales present on fruits were dead and only caused cosmetic damage of the fruits. These results suggested that we should adopt alternative economic thresholds not based on cosmetic damage of fruits in order to use natural enemies to control the pest practically.