Abstract
Racemomycin-D showed strong delayed insecticidal action against the 5th instar larvae of silkworm, Bombyx mori. The pattern of toxic action was similar to that seen in mammals. In order to clarify the mechanism of insecticidal action of racemomycin-D, the authors investigated the distribution of racemomycin-D into the tissues of the larvae. In groups of larvae given various doses of racemomycin-D (50-200μg/g), the concentration of racemomycin-D in the blood decreased gradually in all cases, but the decrease rate was lower than that found in mammals. Racemomycin-D was not excreted in the feces. Racemomycin-D was accumulated in larger quantities for a longer time in the Malpighian tubules than in any other tissue. Change of color of the Malpighian tubules was observed visually. These phenomena resemble the findings in mouse and rat described in a previous report, namely, in the mammals, racemomycin-D was accumulated in large quantities for a long time in the kidney, and the organ turned white.
