抄録
イヌホタルイの発生がアカスジカスミカメの発生と斑点米被害に与える影響を明らかにするため,イヌホタルイ発生水田とイヌホタルイを除草した水田において,アカスジカスミカメの発生消長および斑点米発生率について比較した.イヌホタルイ発生水田ではイネの出穂前から成虫の発生が認められ,出穂後の成虫密度も高まった.また,イネの出穂期前後には幼虫の発生が認められ,これはイヌホタルイに産下された卵に由来する個体と考えられた.斑点米発生率はイヌホタルイ発生水田においてイヌホタルイ除草水田より高くなった.このことから,イヌホタルイの発生はアカスジカスミカメの水田内への出穂前の早期侵入の誘因となり,水田内の発生密度を高め,斑点米発生を助長する原因となることが明らかとなった.
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.
