Scirpus juncoides Roxb. var. ohwianus is a cyperaceous weed species found in rice fields and has been reported as an alternative substrate plant for the egg deposition of the sorghum plant bug, Stenotus rubrovittatus. The seasonal occurrence of S. rubrovittatus and its damage to rice grains were investigated in S. juncoides-infested and non-S. juncoides-infested rice fields in 2005 and 2006. In S. juncoides-infested rice fields, the immigration of S. rubrovittatus adults started prior to the heading period of rice plants, and nymphs and adults of the next generation were also observed in the field. In non-S. juncoides-infested rice fields, S. rubrovittatus adults immigrated into the fields after the rice plant heading period and very few nymphs were observed throughout the survey period. The percentages of rice grains damaged by S. rubrovittatus in S. juncoides-infested rice fields were higher than those damaged by S. rubrovittatus in non-S. juncoides-infested fields. These results suggest that weed management in rice fields is essential for reducing the extent of plant bug damage to rice grains as well as for managing weeds in the original habitat of plant bugs.
