Mechanisms of insecticidal action of deoxypodophyllotoxin (anthricin). II. Histopathological studies on tissues of silkworm larvae intoxicated by deoxypodophyllotoxin

It was previously reported that deoxypodophyllotoxin (I) shows strong insecticidal activity against several kinds of insects, including the 5th instar larvae of silkworm, B. mori. In the present work, in order to clarify the mechanisms of insecticidal action of I, histopathological examination of the fat body, the skin, the Malpighian tubules, and the ventriculus of intoxicated silkworm larvae was carried out and destruction of the epidermal cells was noted. No abnormality of the Malpighian tubules or the ventriculus in the treated larvae was found. Although the fat body cells were also destroyed, the extent of destruction was almost the same both in the administered group and in a fasted group. Therefore, it is unlikely that the primary site of action of I is the fat body cells.