Toxicity And Repellent Effects Of Essential Oils Against Haemaphysalis Longicornis(Acari:Ixodidae)

Ticks are a kind of haemorrhagic arthropods that can parasitize on the body surface of humans and animals,and can carry and transmit a variety of pathogens.Ticks and tick-borne diseases are increasingly threatening the health of humans and animals,attracting much social attention.Haemaphysalis longicornis belongs to Haemaphysalis,Ixodidae,and is a widespread tick species in China.It can transmit a variety of tick-borne diseases such as fever with thrombocytopenia syndrome,Babesiosis and rickettsiosis.The use of chemical acaricides is the most traditional way to control ticks,but due to its single mechanism of action,environmental pollution,easy to induce tick resistance and other shortcomings,people urgently need to find efficient,environmental protection,low toxicity alternatives.In this study,thirteen essential oils were screened out through pre-experiment,among which Cinnamomum cassia Presl oil、Cinnamomum camphora oil、Ilex purpurea Hassk oil、Eugenia caryophyllata oil、Cymbopogon martini oil、Pimenta racemosa oil were toxic essential oil,Artemisia argyi H.oil、Rhizoma chuanxiong oil、Citrus reticulata Blanco oil、Nepeta cataria L.oil、Abies fabri（Mast.）Craib oil、Myristica fragrans oil、Pelargonium graveolens oil were repellent essential oil.The essential oils were analyzed by gas chromatography-mass spectrometry（GC-MS）.In this study,the insecticidal effects of six toxic essential oils against H.longicornis at three different stages of larve,nymph and adults were determined by in vitro immersion method.Three essential oils with the most significant insecticidal activities were screened out namely C.cassia Presl oil、I.purpurea Hassk oil and P.racemosa oil.In addition,the highest content ingredient in C.cassia Presl essential oil,the highest content of methyl salicylate in I.purpurea Hassk essential oil,and the highest content ingredient in P.racemosa essential oil,namely eugenol,were used to kill unfed ticks and unfed adults.At the same time,the activity changes of Ach E,Car E and CAT of essential oils and top components in unfed adult ticks were determined at median lethal concentration（LC50）.The repellent effect of seven essential oils on H.longicornis was determined by the repellent experiment.The results are as follows:1.Gas chromatography-mass spectrometry（GC-MS）was used to analyze the components of six essential oils with good toxicity effect and seven essential oils with good repellent effect screened out through pre-experiment.The main composition of C.cassia Presl essential oils was trans-cinnamaldehyde,the main components in I.purpurea Hassk oil was methyl salicylate,main ingredients of P.racemosa essential oil was eugenol,the main composition of C.martini essential oil were phenethyl and alcohol,the main components of the C.camphora oil were diethyl phthalate,the main compositions of E.caryophyllata essential oil was hexadecanoic acid,2-methylpropyl ester and eugenol,and the main composition of A.fabri（Mast.）Craib oil was diethyl phthalate,the main component in R.chuanxiong oil wasα-terpineol,the main compositions of C.reticulate Blanco essential oil were diethyl phthalate and D-limonene,the main components of the N.cataria L.oil was diethyl phthalate,the main components of the A.fabri（Mast.）Craib essential oil was diethyl phthalate,the main components of M.fragrans oil was isobutyl palmitate,the main component of P.graveolens essential oil was geraniol.2.In the toxicity test of C.cassia Presl essential oil,C.camphora essential oil,I.purpurea Hassk essential oil,E.caryophyllata essential oil,C.martini essential oil,P.racemosa essential oil against H.longicornis,six kinds of drugs all showed different degree of ticks killing activity.C.cassia Presl essential oil,C.camphora essential oil and I.purpurea Hassk essential oil showed significant killing activity against larva,with LC₅₀ of 0.02mg/m L,0.17mg/m L and 0.25mg/m L,respectively.C.cassia Presl essential oil,I.purpurea Hassk essential oil and P.racemosa essential oil showed significant killing activity against unfed nymph.LC₅₀ was 0.29mg/m L,1.56mg/m L and1.56mg/m L,respectively.C.cassia Presl essential oil,I.purpurea Hassk essential oil and P.racemosa essential oil also had significant killing activity against unfed adult ticks.LC₅₀ was 0.66mg/m L,1.07mg/m L and 0.51mg/m L,respectively.3.The above results showed that C.cassia Presl essential oil,I.purpurea Hassk essential oil and P.racemosa essential oil all have significant killing activity on nymphs and adults of H.longicornis.The composition analysis for three kinds of plant essential oils content of the highest single component respectively trans-cinnamaldehyde,methyl salicylate and eugenol,in the toxicity test against nymphs and adults,three single components also showed strong killing activity.The median lethal concentrations(LC₅₀)of trans-cinnamaldehyde,methyl salicylate and eugenol against nymphs of H.longicoris were 0.54mg/m L,0.56mg/m L and 0.93mg/m L,respectively.The median lethal concentrations(LC₅₀)of trans-cinnamaldehyde,methyl salicylate and eugenol to unfed adults were 2.11mg/m L,0.26mg/m L and 1.83mg/m L,respectively.4.Compared with the control group,the enzyme activities of unfed adult H.longicornis at half lethalconcentration of essential oils and single components were as follows:（1）I.purpurea Hassk oil、C.cassia Presl oil、P.racemosa oil and methyl salicylate had a certain degree of effects on Ach E activity,other essential oils and single components had no significant effect（P<0.05）.（2）All essential oils except E.caryophyllata oil and trans-cinnamaldehyde had a certain degree of effects on Car E（P<0.05）.（3）I.purpurea Hassk oil and trans-cinnamaldehyde and eugenol had a certain degree of effects on CAT activity（P<0.05）.These results indicate that different essential oils have different effects on the same or different enzymes in ticks,indicating that different essential oils have different biological activities and different mechanisms of action,which may be related to the complexity of essential oils and the interaction between different components.5.The repellent effects of N.cataria L.essential oil,P.graveolens essential oil,R.chuanxiong essential oil,A.fabri（Mast.）Craib essential oil,M.fragrans essential oil,A.aegyi essential oil and C.reticulata Blanco essential oil on H.longicornis were measured,and the repellent effects of A.aegyi essential oil,C.reticulata Blanco essential oil,A.fabri（Mast.）Craib essential oil and N.cataria L.essential oil were the most obvious.EC₅₀ were 1.04μg/cm²,1.67μg/cm²,1.74μg/cm²and 2.52μg/cm²,respectively.These results suggest that essential oils may be an effective substitute for synthetic acaricides in future tick control.