Abstract
In peach cultivation in Yamanashi Prefecture, fruit growers used insecticides to control Pseudaulacaspis prunicola（Maskell）（Hemiptera: Diaspididae）, but serious damage occurred. Therefore, we investigated the dominant species of scale insects on peaches. P. prunicola has a closely related species, P. pentagona（Targioni-Tozetii）, and the occurrence period of P. pentagona larvae of the 1st generation has been observed 9–13 days later than that of P. prunicola. However, the dominant species observed was P. prunicola. We suspected a time lag due to climate change between the occurrence of the 1st generation of P. prunicola larvae and the spraying of insecticides. However, the peak time of larval occurrence calculated from the effective accumulated temperature（144.1 degree-days; lower development threshold temperature 10.0°C; calculated from January 1）matched the timing of spraying. Furthermore, we observed the highly control effects of buprofezin at variously timed applications on P. prunicola larvae collected from Japanese plums cultivated under low pest control pressure. Buprofezin has been used as a principal insecticide for P. prunicola in Yamanashi Prefecture. However, the effect of buprofezin on P. prunicola, collected from five peach orchards cultivated by the practice method, was low. This suggests that low sensitivity to buprofezin is one of the causes of the frequent occurrence of P. prunicola.
