Outbreaks, damages in rice plants and ecology of ear-sucking bugs in the Muda area were investigated. Leptocorisa oratorius was the most common species in paddy fields and its density was the highest among the bugs. The high density of this bug was observed at the milkripe stage of rice plants in weedy fields, especially where the Echinochloa crus-galli complex predominated. The harvested rice samples collected from 8 rice mills showed that the total ratio of pecky and empty grains was 8.4-29.7%. Although all of the empty grains were not necessarily attributed to rice bugs, their attacks seemed to cause a serious yield-loss. Caging experiments showed that L. oratorius adults damaged 6.40-7.66 grains/day/adult at maximum, when the adults were released on the panicle at the flowering stage. The relationship between the density of L. oratorius in paddy fields and the number of damaged grains was not clear as indicated by a low regression of the latter to the former (r=0.405). It was therefore difficult to estimate the control threshold from this relationship, The control of weeds, especially E. crus-galli complex, seemed to be the most effective and practical means to reduce rice damages caused by ear-sucking bugs.