Seasonal Changes and Differences in Vegetation, and Interactions between the Vegetation and Two Mirid Bugs（Hemiptera: Miridae）Causing Pecky Rice in Rice Paddy Levees

Abstract

We investigated the vegetation management and occurrence of two mirid bugs, Trigonotylus caelestialium（Kirkaldy）（Hemiptera: Miridae）and Stenotus rubrovittatus（Matsumura）（Hemiptera: Miridae）, causing pecky rice, in rice paddy levees over an area measuring 10 ha in Niigata Prefecture, Japan. Mowing and herbicide application were carried out on the levees several times to manage weeds during the growing period of rice. Major poaceous plants on the investigated levees were Poa annua, Alopecurus aequalis, Digitaria ciliaris, and Echinochloa crus-galli. The two mirid bug species existed either separately or together on levees infested with ear-emerged poaceous plants. In July and August, which are important periods for forecasting the two bugs, D. ciliaris was the major plant and occurrence of the two mirid bugs was almost entirely restricted to the levees infested with ear-emerged D. ciliaris. Ears of D. ciliaris vanished after mowing or herbicide application and re-emerged with growth. As a result, the locations of levees infested with ear-emerged D. ciliaris changed over short periods. The observation results were similar over 3 years, and there were no significant changes in weed management, vegetation, and occurrence of the two bugs in the area. In levees infested with ear-emerged D. ciliaris, the spatial distribution pattern of T. caelestialium was aggregated, and that of S. rubrovittatus was even more aggregated. Despite the difference in the distribution, the locations and areas of levees infested with ear-emerged poaceous plants could be used in indices for regionally forecasting the occurrence of the two bugs.