Abstract: Fluoridetolerant mechanism of silkworm larvae,Bombyx mori was studied by cytochemical method at ultrastructural level associated with excessive ingestion of fluoride. Results showed that excessive ingestion of fluoride could inhibit the acid phosphatase (ACPase) activity both in blood and midgut tissues of silkworm larvae and ACPase activities was decreased as the fluorine content in the mulberry leaves increased. However, ACPase activity in the blood exhibited a sudden rise when the content of fluorine in the food reached a certain level,but that in the midgut tissues kept dropping. It was demonstrated in the present study that this turning point of ACPase activity in the blood was related with the fluoride-tolerance of silkworm varieties,and the increase of ACPase activity in the blood was caused by the release of ACPase from the destroyed midgut tissues, owing to the poison effect by high fluoride content ingested. It is believed that the different effects of fluoride on the ACPase activity in different silkworm varieties reveal the mechanism of fluoride-tolerant ability of silkworm larvae.

Key words: silkworm variety (Bombyx mori), fluoride\|tolerance, acid phosphatase, subcellular localization