| Paederus fuscipes Curtis(Coleoptera: Staphylinidae)is widely distributed throughout the world except Antarctica.The beetle is a kind of important resource insect,because it not only preys on the majority of main kinds of agricultural pests but also its toxin has a strong anti-tumor,antiviral activity.In recent years,with the urban expansion to agricultural fields and other sites,P.fuscipes has invaded into the human setting,and the outbreak of dermatitis linearis has aggravated in a large area of China's southern cities,which has caused great trouble to the daily life of people.Hence,P.fuscipes becomes a new urban pest.Some physical measures for prevention of P.fuscipes have little effect.To date,chemical treatment in infested human settings is the optimal approach used to deal with rove beetle infestations.However,chemical control confers negative consequences(residual toxicities,environmental pollution,and so on)and thus has limited applications in houses.Given the demand for health potion of safety,and environmental protection,this study chose 10 plant essential oils to prevent P.fuscipes adults.Firstly,10 plant essential oils were identified through gas chromatography–mass spectrometry analysis.Then,we screened 10 plant essential oils for the oil with the optimal contact toxicity,fumigant toxicity,or repellent activity against adults of P.fuscipes by using the method of the contact,fumigant and repellent,respectively.Furthermore,we explored the insecticidal mechanism of wintergreen oil in terms of its effect on the activity of acetylcholinesterase(AChE)enzyme and detoxifying enzymes(carboxylesterase,glutathione-S-transferase,and P450);such effect was studied both in vivo by fumigation and in vitro in P.fuscipes male and female adults.The main results were as follows: 1 Analysis of chemical composition of 10 essential oilsTen Essential Oils(wintergreen,peppermint,moxa leaf,linalyl,lemon,eucalyptus,clove,citronella,cinnamon,and sweet wormwood oils)were analyzed by GC–MS.Some results are shown: the dominant component of wintergreen oil is methyl salicylate(99.42%);the major component of cinnamon oil is trans-cinnamaldehyde(99.37%);and the main component of wintergreen oil is clove oil is eugenol(82.63%).2 Screening of plant essential oils as repellents,fumigants,and insecticides 2.1 Screening of plant essential oils as repellentsTen plant essential oils were determined for repellent activity against P.fuscipes at the concentration of 0.1 ?L/cm2.Cinnamon oil showed excellent repellency,as high as 100%,against the beetle for 6 h.Clove oil also exhibited excellent repellence against P.fuscipes.The two oils both showed class–V for 8 h and repellent rate more than 95%.Notably,wintergreen oil alone killed beetles.It can not determine whether the oil had a repellent activity at this concentration.The other essential oils exhibited low or poor repellency.Further experiments were carried out to determine the repellent activities of cinnamon,clove,and wintergreen oil against P.fuscipes at the concentration of 0.01 ?L/cm2.Cinnamon and clove oils showed class–V(1–4 h)and class–IV(6–8 h),but wintergreen oil only exhibited class–I for 8 h.Finally,the repellent activity of cinnamon and clove oils were determined at the concentration of 0.005 ?L/cm2.The repellent activity of the two oils both decreased significantly with time,and the repellent activity of cinnamon oil was significantly higher than that of clove oil at the same treatment time.2.2 Screening of plant essential oils as fumigantsTen plant essential oils were determined for fumigation activity against P.fuscipes at the concentration of 2 ?L/L air.Wintergreen oil showed the excellent and highest fumigant toxicity,and the corrected mortality rates caused by wintergreen oil reached 24% after 1 h of exposure and up to 80% after 8 h.LC50 values of wintergreen oil were 2.680,2.178,2.046,1.765,and 1.591 2 ?L/L air after 1,2,4,6,and 8 h of exposure,respectively.2.3 Screening of plant essential oils as insecticidesTen plant essential oils were determined for contact toxicity activity against P.fuscipes at the concentration of 0.08 ?L/adult.Wintergreen oil showed the greatest contact toxicity,with corrected mortality rates of 40% after 1 h of exposure and up to 82% after 8 h.LC50 values of wintergreen oil were 0.086,0.067,0.062,0.061,and 0.060 ?L/ adult after 1,2,4,6,and 8 h of exposure,respectively.In conclusion,cinnamon oil had best repellent activity against the public health pest P.fuscipes,yet both cinnamon and clove oils may have potential as repellents.Wintergreen oil had optimal contact and fumigant toxicity against P.fuscipes,and it may have potential as insecticides and fumigants.3 Insecticidal mechanism of wintergreen oilThe insecticidal mechanism of wintergreen oil was explored in terms of its effect on the activity of acetylcholinesterase(AChE)enzyme and detoxifying enzymes(carboxylesterase,glutathione-S-transferase,and P450);such effect was studied both in vivo by fumigation and in vitro in P.fuscipes male and female adults.In the in vivo and in vitro experiments on male and female adults,wintergreen oil did not significantly affect the activities of the three detoxifying enzymes.Wintergreen oil significantly inhibited AChE activity in a dose-dependent manner.When wintergreen oil was tested at different times in vivo,the highest inhibition rates of AChE activity were 41.99%(2 h)and 40.91%(4 h)for the male and female groups,respectively;and the lowest inhibition rates of AChE activity were 20.24%(1 h)and 14.88%(1 h)for the male and female groups,respectively.When different doses of wintergreen oil were used for in vivo treatment,the highest inhibition rates were 33.78% and 43.33% in the male and female groups,respectively;and the lowest inhibition rates were 21.20% and 17.87% in the male and female groups,respectively.The lowest and highest inhibition rates corresponded to the lowest(0.909 ?L/L air)and highest doses(1.636 ?L/L air),respectively.When wintergreen oil was tested in vitro,in the male group,the inhibition rate of AChE ranged from 10.37% to 31.06%,and the lowest and highest inhibition rates corresponded to the lowest and highest doses,respectively;in the female group,the inhibition rate of AChE ranged from 20.75% to 35.57%,and the lowest and highest inhibition rates corresponded to the lowest and second-highest dose(2 ?L wintergreen oil),respectively.In summary,the results demonstrated that the mode of action of wintergreen oil may be unrelated to the three detoxifying enzymes,but AChE is a potential key factor in the mechanism of wintergreen oil's optimal insecticidal activity against P.fuscipes. |
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