Study On The Toxicity Of Extracts From The Cosmos Bipinnatus To Tetranychus Urticae Koch

Herbivorous mites are recognized as one of the most difficult to control communities in agricultural production.In recent years,the frequent use of chemical acaricides has led to serious environmental pollution,resistance of harmful mites,and increasing losses of crops.The development of highly efficient and environmentally friendly botanical acaric insecticides is becoming one of the hotspots of pesticide development.In this paper,18 plant extracts were screened for acaricidal activity,and the acaricidal mechanism of Cosmos bipinnatus extracts was preliminarily discussed.The indoor acaricidal activity screening of ethanol extracts from 18 species of 14families collected in mountainous areas around Wafangdian City,Dalian,Liaoning Province was studied.The results showed that the ethanol extracts from 18 species of plants had different contact activity to female adults of Tetranychus urticae Koch.After treated with 10 mg/ml ethanol extract for 24 hours,Cosmos bipinnatus,tobacco and Ginkgo biloba had strong acaricidal effect,and the corrected mortality rate was above90%.Ethanol extracts from Cosmos bipinnatus,Ginkgo biloba,tobacco,violae herba and Begonia sibirica had better inhibition on hatching of Tetranychus urticae Koch eggs.The LC₅₀ of ethanol extracts from Cosmos bipinnatus,ginkgo,tobacco,purple flower and crabapple to female adults of Tetranychus urticae Koch were 3.178,3.642,3.200,5.535 and 5.522 mg/ml,respectively.The acaricidal activity of the Cosmos bipinnatus was full evaluated.Petroleum ether,ethyl acetate,ethanol and methanol were used to extract Cosmos bipinnatus in parallel with four different polar gradient solvents.The acaricidal for female adults and ovicidal tests of four different solvent extracts were carried out,and the virulence to female adults of Tetranychus urticae Koch was determined.The results showed that the extraction rates of methanol and ethanol were relatively high.The contact toxicity of plant extracts from four different solvents of Cosmos bipinnatus against female adult mites of Tetranychus urticae Koch showed that the corrected mortality rates of petroleum ether,ethyl acetate,ethanol and methanol were 54.45%,42.22%,95.53%and89.99%respectively after 24 h of treatment.With the prolongation of treatment time,the miticidal activity of extracts also gradually increased,and after 72 h,the corrected mortality of ethanol extract and methanol extract reached 100%.Among the extracts from four different solvents of Cosmos bipinnatus,ethanol extracts showed strongest contact toxicity to eggs.The Virulence of petroleum ether,ethyl acetate,ethanol and methanol to female adult mites was 5.481,7.385,3.178 and 3.917 mg/ml.The effects of ethanol extract of Cosmos bipinnatus on oviposition inhibition and repellency of mites were studied.The results showed that with the increase of ethanol extract concentration of Cosmos bipinnatus,the oviposition inhibition index and oviposition inhibition rate increased gradually.The oviposition inhibition index was 0.9802 and the oviposition inhibition rate was 99%at the concentration of 12.8 mg/ml at 24 h.The ethanol extracts of Cosmos bipinnatus at different concentrations had different degree of repellent effect on Tetranychus urticae Koch.The repellent effect of 0.8 mg/ml treatment on Tetranychus urticae Koch was weak.The repellent rate was 12.22%at 12 h and there was almost no repellent effect at 72 h.With the increase of treatment concentration,the repellent effect of ethanol extract of Cosmos bipinnatus on harmful mites increased,and the repellent rate of 12.8 mg/ml treatment group to harmful mites reached more than85%after 24 h.The acaricidal mechanism of ethanol extract from Cosmos bipinnatus was preliminarily discussed.After the treatment of Tetranychus urticae Koch with ethanol extract from Cosmos bipinnatus,the appearance of mites gradually changed from smooth body wall,plump body and incessant movement of mites'feet to immobility,contracted size,dry and black color.After treated with ethanol extract of Cosmos bipinnatus,the mite content of protease decreased,the activity of Na⁺,K⁺-ATPase declined,the activity of glutathione mercapto-transferase increased at first and then decreased,the activity of superoxide dismutase and catalase increased,and the change of monoamine oxidase was not obvious.It is suggested that Na⁺,K⁺-ATPase and glutathione mercaptosyltransferase are related to the miticidal mechanism of Cosmos bipinnatus,and oxidative stress is also involved.