STUDIES ON THE TOXICOLOGY OF THE BIOACTIVE MATERIALS FROM TRIPTERYGIUM AGAINST THE IMPORTED CABBAGES WORM (PIERIS RAPAE L.)
Tong Hongyun Chiu Shin-Foon (Department of Plant Protection)
The toxicology effects of plant extracts frrm species of Tripterygium (T. wrlfordii and T. hypoglaucum) on the imported cabbage worm (Pieris rapae) were studied both in the laboratory and in the field. The results showed that the extracts from the root bark of Tripterygium are a strong antifeedant, stomach poison and growth inhibitor. After feeding with the the ethanol extract from the root bark of T. wilfordii or wilforine (an alkaloid from T. hypoglaucum) ,black spots appeared in the larvae. Microscopic examinations of its section showed that the cuticle became thinkened and cancers appeared between the epidermis and endocuticle, the epdiermis was destroyed, the enaocuticle separated from the epidermis and vacuoles fromed.After treatment with wilforine, the respiration of the larvae of P. rapae was markedly affected and their body weight was decreased. After eating the leaves of the cabbage treated with wilforine, the larvae showed paralysis and their respiratory rhythms were not conspicuous. The amplitudes of the respiratory rhythm-waves became lower and the CO2 output decreased, The larvae treated with wilforine and those fully-starved showed the same change trends in body weight and rospiratory rates. Five days after treatment, the larvae were dissected. It was found that the alimentary canal and the fat body were shrivelled, the epithelium of mid-gut and the peritrophic membrane were destroyed. According to these results, it is thought that the lethal mechanism of extracts from T. wilfordii and T. hyponglaucum against the larvae of P. rapae may be as follows. After a slight feeding of the extracts, the larvae shows paralysis. Then the toxic principles of the extracts affects the mid-gut epithelium of alimentary canal.As a result the larvae could not continue to feed. Due to shortage of nutrition, metabolism is hampered. Thus, the larvae finally die of starvation. Result of field plot trials demonstrated that the cabbage plantation was well protected from the damage of the larvae of P. rapae by spraying with the 3% ethanol extract of the root bark of T, wilfordii, and it was showed that the natural enemies of the larvae were not attacke by spraying. No phytotoxicity was observed on cabbages.