沖縄県宮古島におけるイネヨトウ（チョウ目：ヤガ科）とカンシャシンクイ（チョウ目：ハマキガ科）によるサトウキビ芯枯れ被害およびその対策

Borers Sesamia inferens (Walker) and Tetramoera schistaceana (Snellen) cause severe damage to sugarcane shoots, known as dead hearts, and affect sugarcane tillering. We examined the roles of these insects in causing dead hearts in summer-planting and ratoon sugarcane fields on Miyako Island, Okinawa, Japan, by dissecting and investigating damaged shoots. Most of the dead heart shoots were considered to have been caused by infestation of these two borers. The number of dead hearts increased gradually from fall to winter in summer-planting fields, whereas in the ratoon fields it peaked in the spring. In S. inferens, the number of trap catches of adults caught with sex-pheromone were significantly correlated with the ratio of dead hearts of shoots, excluding those under suppression with insecticide at summer planting. Fipronil bait applied in furrows at the time of planting of sugarcane stalks in summer was more effective in reducing the incidence of dead hearts than benfracarb or carbosulfan granules applied in the same way. In the tillering stage, chlorantraniliprole flowable was effective in preventing dead heart shoots. In ratoon fields, no significant difference was observed in the incidence of dead hearts treated with two insecticides, fipronil bait and benfracarb granules, irrespective of whether they were mixed with soil by a machine or placed in furrows. Our results indicated effective control of borer damage with fipronil bait treatment at the time of planting and chlorantraniliprole flowable at the time of tillering, and the possibility of adopting cheaper insecticides in ratoon fields.