Crop Losses in Rice Ecosystems Due to Gall Midge (Orseolia oryzae Wood-Mason) Damage

The database created from the All India coordinated insecticide control experiments in rice from 1967 to 1992 was used to derive empirical estimates of gall midge induced yield losses in rice ecosystem. The severity of silver shoot damage was higher in the rainfed lowlands. Each percent damage due to gall midge manifesting as silver shoots had a much greater impact on rice yield in rainfed lowlands than in the irrigated ecosystem. In both ecosystems gall midge damage had a statistically significant effect on yield. Several insecticides showed controlling effect on the incidence of gall midge in both ecosystems studied, but none could totally prevent silver shoot formation. In the irrigated ecosystem, with two applications of some insecticides, grain yields increased by 49 to 68%. But, in the rainfed lowlands, the grain yield increased by 33 to 45% only. Infestation at low levels (5–10% silver shoot) was considered to be within the economic injury level not requiring any plant protection action. From 813 experimental units from 26 years data, our yield loss projections for damage due to 1% gall midge induced silver shoot damage is 3.5% loss. In terms of grain loss over ecosystems, 1% gall midge induced silver shoot damage is 147 kg/ha. In irrigated ecosystem, 1% gall nudge induced silver shoot damage resulted in 3.3% or 141 kg/ha yield loss while, in rainfed lowlands, 1% gall midge induced silver shoot damage caused 5% or 240 kg/ha yield loss. In view of the enormous yield losses caused by an occasional and severe epidemic outbreak, diversification of genes of resistance to Orseolia oryzae in breeding program is suggested in addition to intensifying research on the use of parasites to control this pest.