Abstract
Isolated from Dictamnus dasycarpus Turcz., fraxinellone exhibited multiple bioactivities against insects. In the present paper, the changes of digestive enzymes and detoxification enzymes of Mythimna separata Walker (5th instar larvae), treated with fraxinellone, were investigated. Compared with those of the control, the α-amylase activity of the fraxinellone-treated 5th instar larvae was inhibited, whereas the level of their protease activity was increased. Based upon further studies on the specific proteases, the levels of the active alkaline trypsin-like enzyme (BApNA as the substrate) and the chymotrypsin-like enzyme (BTEE as the substrate) activities of the treated larvae were declined; however, the level of activity of the weak alkaline trypsin-like enzyme (TAME as the substrate) of the treated ones was increased. Meanwhile, the activities of two detoxification enzymes, such as carboxylesterase (CarE) and glutathione S-transferase (GST), of the treated larvae were increased to some extent, but the activities of NADPH-P450 reductase and O-demethylase of the treated ones declined. Therefore, protease (especially the weak alkaline trypsin-like enzyme), CarE and GST played important roles in the metabolism of fraxinellone in the midgut of Mythimna separata (M. separata).
Highlights
Insect pest management is facing an economic and ecological challenge worldwide due to human and environmental hazards caused by the majority of synthetic pesticide chemicals
The activities of two detoxification enzymes, such as CarE and glutathione S-transferase (GST), of the treated 5th instar larvae were increased to some extent
The activities of α-amylase, lipase, and cytochrome P450 were inhibited by fraxinellone, but the activities of protease, carboxylesterase and glutathione S-transferase were increased
Summary
Insect pest management is facing an economic and ecological challenge worldwide due to human and environmental hazards caused by the majority of synthetic pesticide chemicals. Botanicals containing active insecticidal phytochemicals play an important role in protecting plants from herbivores and appear to be promising in addressing some of these problems Through diverse methods, such as acute toxicity, enzyme inhibition, and interference with the consumption of food [2], plant secondary metabolites are deleterious to herbivores. Further histopathology research revealed that the organelles of M. separata midgut were changed clearly after treatment with fraxinellone [20] It is well-known that digestive enzymes and detoxification enzymes of the insect midgut are involved in the detoxification or metabolism of xenobiotics [21]. The changes of digestive enzymes (α-amylase, lipase, total protease and specific protease) and detoxification enzymes (CarE, GST and P450) of M. separata (5th instar larvae) treated by fraxinellone were investigated. The relationship between the metabolism of fraxinellone and the above two kinds of midgut enzymes was discussed
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