Effects of fraxinellone on the midgut ultrastructural changes of Mythimna separata Walker

Extracted from the dried root bark of Dictamnus dasycarpus Turcz., Family Rutaceae, fraxinellone exhibited multiple bioactivities, e.g. feeding-deterrent, growth-control and toxic activities against insects. We investigated the effect of fraxinellone on fifth instar larvae of eastern armyworm, Mythimna separata Walker. Through traditional stomach-poison method, fraxinellone showed the delayed and strong stomach-poison activity. Light and electron microscope observations revealed, treatment with 20 mg/mL fraxinellone, increasing damages of the larvae midgut epithelium along with time. Fraxinellone destroyed the peritrophic membrane of the midgut of larvae of M. separata. The organelles of treated larvae of M. separata changed obviously, e.g. the rough endoplasmic reticulum dilated, some of mitochondrial cristaes disappeared and got vacuolated, the wall of globet cell invaginated, the inner organelle disordered, the chromatin became concentrated, and the quantities of secondary lysosome increased. Meanwhile, fraxinellone could let microvilli rupture or incline, even partially fall off.