Preliminary Studies On The Insecticidal Activities And The Action Mechanisms Of Two Magnolol Derivatives

In recent years,discovery of efficient and environmentally friendly new pesticides from the natural active precursors has become one of the important procedures to develop new agrochemicals.Magnolol,a neolignan with diphenol structure,shows a broad of pharmacological properties,including anticancer,antivirus,antioxidative and antibacterial activities.Recently,the insecticidal and antifungal activities in the agricultural field were also reported.In this paper,the insecticidal activities of two magnolol derivatives,XHXN-2 and XHXN-3,were firstly studied against the larvae of Mythimna separata Walker,Plutella xylostella Linnaeus and Brevicoryne brassicae Linnaeus.Then,according to the poisoned symptoms,histopathology researches and enzymology,the action mechanisms of XHXN-2 and XHXN-3 against M.separata were preliminarily studied.Main results were obtained as following:1.The insecticidal activities of XHXN-2 and XHXN-3 against M.separata,P.xylostella and B.brassicae were tested.?1?It showed that XHXN-2 exhibited obviously stomach toxicity against the third instar larvae of M.separata after treatment of 48 h;its LC₅₀ and LD₅₀ values against the third instar larvae of M.separata were 0.4710 mg/mL and 0.5052 ?g/larvae,respectively;its LC₅₀ value was 0.2448 mg/m L against the third instar larvae of P.xylostella larvae after treatment of 48 h.XHXN-3 also displayed the stomach toxicity against the third instar larvae of M.separata and P.xylostella after treatment of 48 h;its LC₅₀ and the LD₅₀ values against M.separata were 1.3092 mg/m L and 1.6082 ?g/larvae,respectively;its LC₅₀ value against P.xylostella was 2.3974 mg/mL.?2?After treatment of 48 h,only XHXN-2 had the contact poisoning toxicity against the third instar larvae of M.separata,and its LD₅₀ value was 7.5812 ?g/larvae.XHXN-2 and XHXN-3 showed the strongly contact poisoning toxicity againgt the B.brassicae after treatment of 48 h,and their LD₅₀ values were 1.5357 ?g/larvae and 2.8947 ?g/larvae,respectively.?3?Two compounds had no significant antifeedant activity against M.separata,P.xylostella and B.brassicae.2.The poisoned symptoms of sixth instar larvae of M.separata treated with XHXN-2 and XHXN-3 were as follows: the poisoned insects exhibited vomit and diarrhea,which was typical stomach toxicity symptom;the body of poisoning insects was collapsed and bended.The larvae were severely dehydrated to die ultimately.3.Through transmission electron microscopy,the midgut ultrastructure of M.separata was largely affected after treated by XHXN-2 and XHXN-3: the mitochondria were disintegrated with swelling and vagued cristaes;microvilli was fractured and decreased;nuclear membrane was ruptured,and nucleolus overflowed.XHXN-2 showed the obviously ultrastructural damage on mitochondrial and nuclear membrane in the midgut.However,XHXN-3 had serious destruction on microvilli and sarcoplasmic reticulum in the midgut.It showed that the effect of XHXN-2 and XHXN-3 on tissue and organelle in the midgut of the poisoned insects might be the reason leading to the poisoned insects' death.4.After treated with XHXN-2,the activities of three midgut detoxification enzymes?GST,CarE and NCR?of fifth instar larvae of M.separata were improved to some extent.Accordingly,the activities of GST and NCR of fifth instar larvae of M.separata treated with XHXN-3 were increased,but it did not affect the Car E.Based on their influence on the midgut ultrastructure and detoxification enzymes of M.separata,it suggested that XHXN-2 and XHXN-3 might be a digestive poison.