Residue of MPP on mulberry leaves and its toxicity to the silkworm, <i>Bombyx mori</i>

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  • ＭＰＰ（バイジッド）の桑葉残留とカイコに対する毒性
  • MPP バイジット ノ ソウヨウ ザンリュウ ト カイコ ニ タイスル ドクセ

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Residue of an organic phosphorous insecticide, MPP [0, 0'-dimethyl-o-(3-methyl-4-methyl mercaptophenyl) thiophosphate] on mulberry leaves and its toxicity to silkworm larvae were investigated.<br>1. MPP sulfoxide as the main oxidized product of MPP was detected on mulberry leaves on the 5th day after the application by means of gas chromatography.<br>2. The total residue of MPP and MPP sulfoxide on the 22th day after the application was 6.34ppm on leaves of potted mulberry trees which had been left out of doors and kept in no-rainfall condition. Almost all silkworm larvae fed on the leaves died.<br>3. The total residue of MPP and MPP sulfoxide on the 15th day after the application was 0.68ppm on leaves of the potted mulberry trees which had been left in the field. Silkworm larvae reared with the leaves grew nearly normally except for a few undergrown larvae. Therefore, the tolerance of residue of MPP and MPP sulfoxide on mulberry leaves was assumed to be less than 0.5 and 0.1ppm, respectively.<br>4. LD50 values (μg/g body weight) of MPP, MPP sulfoxide and MPP sulfone were almost the same by topical administration, but, by oral administration, 120μg, 21μg and 22μg, respectively. These results showed that the oxidized products of MPP were six times as toxic as MPP and that oxidized products should be assayed for the determination of the residual duration of MPP to silkworm larvae.

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