Abstract

Yield-related responses of rice plants to artificial infestation of 5 adult Aspavia armigera per peduncle at 0, 7, 14, 21 days after flowering were examined to determine the critical stage of rice for Aspavia armigera infestation. Damage was also assessed at 7 days after flowering, which was the critical stage of rice, under different bug densities - 0, 2, 4, and 8 bugs per peduncle. The highest grain weight loss of 70.0%, which was significantly different from those recorded at 14 days after planting (DAF) and 21 DAF (40% and 39.7%, respectively), occurred at 7 DAF which was the milk stage. Similarly, significantly lower paddy and head weights which were about 48% of that of the control were obtained at 7 DAF, while higher percentage of floating grains caused by A. armigera infestation was obtained at 7 and 14 DAF compared to other times. With increasing insect density there was a corresponding significant increase (P < 0.05) in floating grains and grain weight loss, and reduction in head weight, paddy weight and grain weight. At 2 bugs per peduncle caused a significant reduction in rice yield parameters in both upland and lowland varieties and is therefore the damage threshold for the varieties tested.

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