Studies on the resistance of rice-plant against the attack of rice-stem-borer (Chilo simplex Butler). : (II) Interrelation between the plant character and larvae intrusion in the first generation of rice-stem-borer. (Preliminary report)

摘要

(1) Newly hatched larvae were set on leaf-blades of seedlings of various varieties of different ages, and the behavior of larvae, position of intrusion and plant character were investigated in the laboratory. (2) Many larvae set on leaf-blades creep generally upward seeking the spot to bore and some larvae hung themselves from the top of leaf-blade spitting the yarn. But the majority of larvae soon creep down again, wandering about the ligules and auricles, and at last come to near the surface of water. Then larvae crecp a little way upward again, and begin to bore. It needs usually long time (about one hour) to seek the spot to bore, but very short time from boring till intrusion. (3) In genral, the openings of intrusion located on some definite position of leaf-sheath, namely on the lower part of younger seedlings and upper part of aged seedlings. And the openings were found on the parenchymatous parts between each vascular bundle near the midrib, especially on the wider part than the breadth of the larvae head. (4) The percentage of the intruded larvae into the tissue or of the remainder found ontside the plant, showed the grade of resistance of plant against intrusion. This grade was fairly different among varieties and also markedly varied in accordance with the age of seedling. (5) Generally speaking, larvae did not gnaw at the part of vascular bundles. The loci of gnawing had no relation with the width of the parenchymatous parts, but the openings of intrusion were generally found on the wider part of parenchymatous parts than the breadth of the larval head. Among varieties the correlation between the percentage of the intruded larvae and the width of intervascular parenchymatous parts was fairly close. (6) Thus we can come to the conclusion that the width of the parenchymatous parts of intervascular bundles of the leaf-sheath is one of the chief factors to decide the grade of resistance of plant against larvae intrusion.