The mechanisms of delayed insecticidal action of streptothricin antibiotics. II. Effect of racemomycin-D on excretion function of the 5th instar larvae of silkworm, Bombyx mori Linne.

Abstract

Previously, in order to clarify the mechanisms of the insecticidal action of streptothricin antibiotics, we had investigated the distribution of racemomycin-D into the tissues of the 5th instar larvae of silkworm, Bombyx mori, and reported that racemomycin-D accumulated in larger quantities for a longer time in the Malpighian tubules than in any other tissue. In this work, in order to clarify the mechanism of the insecticidal action in more detail, we investigated the Malpighian tubules of the larvae histopathologically and confirmed the occurrence of severe delayed damage. It is noteworthy that streptothricin antibiotics show strong nephrotoxicity in mammals. At 24 h after injection, which was the onset time of the damage to the Malpighian tubules, both the blood level and excretion amount of uric acid were increased, and they subsequently increased much further as the damage became more severe. Thus, through histopathologic examination and analysis of uric acid levels, we showed that the onset time of delayed toxicity of racemomycin-D in the organs of the insects was at 24 h after injection.