Abstract
From 1954 to 1957 at five localities in Tokushima prefecture, Shikoku, ethyl-parathion emulsion, as a 0.02% solution, was sprayed once for the first generation larvae and as 0.04% solution once or twice for the second generation larvae of the rice stem borer, Chilo supressalis WALKER, and yields and the percentage of injured stem of the rice plant were recorded. When comparisons were made between sprayed and unsprayed plots at each locality, in 8 test examples the yield was apparently higher in the sprayed plot than in the unsprayed plot, and in 5 other examples there were no substantial differences in the yield between sprayed and unsprayed plots. From the results obtained, it was estimated that the insecticidal application brings on an economic effect when the percentage of injured stem in unsprayed plot is above 2% at the end of the period of injury of the first generation, and above 3% at the same period of the second generation. Also, the percentage of injured stem at above or below 2% at the end of the first generation might be expected when it is above or below 6.0±3.2% (2 Sx) at just before the application time for the first generation. In the same way, that at above or below 3% at the end of the second generation might be able to presume when it is adove or below 2.3±1.3 (2 Sx) at the end of the first generation.
