Effects of rice panicle age on quantitative and qualitative injury by the rice stink bug (Hemiptera: Pentatomidae)

Greenhouse experiments were conducted to evaluate the effects of panicle age on quantitative and qualitative injury caused by rice stink bug, Oebalus pugnax pugnax (Fab.), infestations on rice, Oryza sativa L. The effects were measured at two infestation levels (one and two bugs per panicle) and compared with an undamaged control. Percentage of empty grains and average weight of filled grains (quantitative injury) and percentage of pecky rice (qualitative injury) were evaluated at grain maturity. Regardless of infestation level, insect feeding during anthesis and the early milk stage of grain development (first 8 d after anthesis) caused substantially higher numbers of empty grains than feeding during later grain development and the control. Average grain weights were lower in infestations during anthesis and milk stage and higher in infestations during later grain development and the control. Pecky rice was significantly higher during late milk and soft dough stages, 9-16 d after anthesis, compared with remaining stages of grain development and the control. Injury was greater in the experiment in which panicles were infested with two bugs. Pecky rice was associated with highly significant reductions in germination of the grains. The data suggest that rice is most vulnerable to rice stink bug injury during the first two weeks after anthesis, and that the major effects of stink bug feeding change as panicles age.