北海道におけるアカヒゲホソミドリカスミカメによる斑点米形成時期の推定

抄録

In August, ethiprole, a phenylpyrazole insecticide（50ppm, 100Liters/10ares）was sprayed several times to control the rice leaf bug Trigonotylus caelestialium in Iwamizawa, Hokkaido. The insecticide was sprayed every 7 to 10 days on four different starting days, August 1, 8, 17, and 22, with the last treatment performed on August 29. In the no-spraying area, many adult bugs were collected in early August up to mid-August by net sweeping. They were considered as those that had migrated from the surrounding area. After August 20, both nymphs and newly emerged adults were collected in small numbers. In the control areas, no or few bugs were collected after the spraying started. A split-hull paddy was observed after mid-August, and its ratio increased thereafter. The percentages of pecky rice caused by the bug for each treatment were 0.29, 0.31, 0.35, and 0.69%; the percentage was 2.67% in the no-spraying area. These results showed that rice grains are injured mainly after mid-August by nymphs and newly emerged adults of the bug and that this period is identical to the increasing period of the split-hull paddy.