It has been confirmed that the 1st brood larvae of the rice stem borer, Chilo suppressalis WALKER, can be killed when γ-BHC is applied in the paddy field soil before transplanting rice seedlings. It is not clear, however, whether the γ-BHC is absorbed from roots and translocated into stems and leaf sheaths or the γ-BHC reaches the borer zone of the stem by capillary action. In order to make clear this point, radioactive γ-BHC was applied in the experiment described below. 9.4mg of γ-BHC-1-C¹⁴, having 0.4μc/mg, was added to 1 litre of water. Some undissolved γ-BHC crystals remained in the solution. Therefore, C¹⁴-γ-BHC used for culture solution of rice plants was less than 9.4ppm.<br>Before testing, rice seedlings of about 40-50cm in height were cultured in water for 1 week to develop new roots. After immersion of the roots of the rice seedlings in culture solution containing radioactive γ-BHC for 65 or 119 hours, the treated seedlings were exposed on X-ray films for about 3 months. Fig. 1 shows the radioautogram, and Fig. 2 shows partial enlargement of the stem part. As seen in these autograms, it is clear that γ-BHC is absorbed from roots and translocated to stems and leaves through vascular bundles. After the radioautography, the leaves and stems were pulverized and extracted with n-hexane. The extract was run by MIUCHELL's paper chromatographic method. The paper chromatogram was scanned by a gas flow counter. Radioactivity was found at the Rf corresponding to γ-BHC, as shown in Fig. 3.<br>In another series of experiment, stems of the rice seedlings were applied with absorbent cotton soaked with vaseline at 4-5cm from the stem base, to prevent creeping of the radioactive γ-BHC by capillary action. After immersion of the roots of the rice seedling in radioactive γ-BHC solution for 65 hours, the vaselined cotton was extracted with acetone and made to 25ml. Aliquots of the extract were assayed for radioactivity by using a gas flow counter. The radioactivity was detected at a high level in the vaseline, and confirmed to be γ-BHC, by scanning the paper chromatogram, as seen in Fig. 4.<br>It is considered that γ-BHC dissolved in water is absorbed by roots and translocated to stems and leaves, but it also creeps up the surface of leaf sheaths by capillary action. Although it is still difficult to conclude which is the major route causing death of the borers living in the rice stem, when γ-BHC is applied to irrigation water from the surface the route via the leaf sheath surfaces seems to be main as compared with the route via rooot systems and through translocation streams.