Oxidative stress induced by destruxin from Metarhizium anisopliae (Metch.) involves changes in glutathione and ascorbate metabolism and instigates ultrastructural changes in the salivary glands of Spodoptera litura (Fab.) larvae

The cyclodepsipeptidic mycotoxin, destruxin, produced by Metarhizium anisopliae is known for its larvicidal properties. The crude destruxin-treated Spodoptera litura larvae revealed a decrease in thiol content and an increment in oxidation of glutathione to glutathione disulfide and ascorbate to dehydro ascorbate in a dose- and time-dependent manner. An increase in the levels of protein carbonyls and the free radicals, hydrogen peroxide and hydroxyl radical was also observed. These provide a clear indication of oxidative stress. Upon ingestion, destruxin causes serious damage to the epithelial cells of the midgut. We report the ultrastructural effects of crude destruxin on the salivary glands of 9-day-old S. litura larva after 24 h of treatment with the mycotoxin at a dosage of 0.147 μg/g body wt. (LD50). The transmission electron microscopic observations revealed characteristic changes in the salivary glands of S. litura which include detachment and damage of the microvilli, epithelial cell vacuolization, bleeding of the epithelial cells into the salivary gland lumen and disruption of the epithelial cell membrane. This investigation focuses salivary glands also as the target organ of destruxin apart from the already known midgut, Malphigian tubules and haemocytes.