| Stored-product insect pests can cause great harm to the weight and quality of stored grain,and its prevention and control is a long-term research hotspot in the world.Booklice（psocids）,belonging to Psocoptera,Liposcelidae and Liposcelis,are an important stored-product pests.When a large number of booklice occur,they will reduce the weight of food or cause mildew,and the food will be polluted by their excreta and corpses;In addition,booklice can also spread germs and thus pose serious threaten on people’s health.It is very difficult to control booklice because of its small size（easy to be ignored）,short generation duration,strong fecundity（rapid population establishment）,strong adaptability and rapid development of insecticides resistance.In view of the indoor outbreak of booklice,due to fewer environmental-friendly insectides,research and development or screening of high efficiency and low toxicity insecticides suitable for controlling this pest in human life areas are becoming urgent issues.Presently,chemical control technology is the main method for the prevention and control of booklice,but there are only a few kinds of insecticides can be taken into account in stored grain system.The extensive use of a single insecticide leads to the rapid development of insecticides resistance and increase the difficulty in controlling of booklice.Therefore,the sensitivity of booklice to stored grain protectants should be evaluated and the sensitivity baseline should be established;Finding new combinations of stored grain protectants or alternative fumigants has become an urgent need for resistance management of booklice.In this thesis,four commonly used stored grain protectants and eight plant essential oils were selected,and the potential control effect of the above agents on booklice by measuring the insecticidal activity of stored grain protectants alone or in combinations were systematically evaluated.Meanwhile,based on comparative transcriptome analysis,the molecular networks under different insecticides treatments were discussed in a booklouse for the first time,and these results will provided basic data for clarifying the molecular mechanism under forming of booklice resistance to insecticides.The main results are listed as follows:1.Toxicities of different stored grain protectants alone or in combination to booklice were determinedThe sensitivity of five species of booklice（Liposcelis bostrychophila,L.entomophila,L.decolor,L.tricolor,L.yangi）to four stored grain protectants（malathion,deltamethrin,beta-cypermethrin,pirimiphos-methyl）was determined.Meanwhile,the optimal ratio and efficiency of the combination of organophosphorus and pyrethroid stored grain protectants against L.bostrychophila,were also evaluated.L.bostrychophila,L.entomophila,L.decolor,L.yangi had the highest sensitivity to malathion,with LD50of 0.131μg/cm2,0.136μg/cm2,0.245μg/cm2,and 0.202μg/cm2,respectively a L.tricolor had the highest sensitivity to deltamethrin（0.041μg/cm2）.The toxicity of malathion to different geographical populations of L.bostrychophila was arranged from0.060μg/cm2 to 0.131μg/cm2.It can be seen that there is no significant difference in the sensitivity of different geographical populations after long-term laboratory domestication.In addition,the toxicity of different combinations of two kinds of stored grain protectant on L.bostrychophila showed that the optimal ratio of malathion to deltamethrin was 4:5,and the synergistic rate was 40.20%;The optimal ratio of pirimiphos-methyl to beta-cypermethrin was 2:1 and the synergistic rate was 50.53%.In conclusion,organophosphorus and pyrethroid stored grain protectants have high toxicity to Liposcelis species,and different booklice have different sensitivity to stored grain protectants,but organophosphorus and pyrethroid stored grain protectants have good killing effect on booklice.It is worth mentioning that the booklice in this study are all rasied for more than 100 generations in the laboratory.The LD50 in the study can be used as the sensitive baseline for booklice pests,which provides a basic basis for monitoring the resistance of these pest against the above stored grain protectants.Furthermore,the combination of stored grain protectants with different action mechanisms has synergistic effects on booklice.Therefore,in the field control,the dosage of insecticides can be reduced through the combination of different insecticides,which is also one of the important strategies to delay the development of insecticides resistance in booklice.2.The fumigation activity of eight essential oils,and the effective of allylisothiocyanate（AITC）in combination with stored grain protectants against booklice were evaluatedIn this study,the fumigant activities of different essential oils against L.bostrychophila were evaluated.The fumigation time of AITC was set as 0.5 h,while that of other essential oils was set as 24 h.The fumigation results(LC50)showed that the sensitivity of L.bostrychophila to plant essential oil from high to low was:AITC（1.379μL/L）>L-carvone（4.103μL/L）>4-terpineol（4.257μL/L）>Melaleuca leucadendron（4.597μL/L）>Eucalyptus robusta（4.762μL/L）>Cinnamomum cassia（6.272μL/L）>Camellias（6.337μL/L）>Lavandula angustifolia（9.000μL/L）.It was found that the toxicty of AITC was significantly higher than other essential oils through the confidence interval analysis of LC50.Therefore,AITC was used in combination with two grain storage protectants（pirimiphos-methyl to beta-cypermethrin）for further investigating the insecticidal efficacy.Results showed that when combined the AITC(LC30,2.4μL/L)with LD30of pirimiphos-methyl（0.29μg/cm2）and LD50 of pirimiphos-methyl（0.35μg/cm2）,the synergistic toxicity index was 50.04 and 55.45,and the corrected toxicity ratio was1.22 and 1.21,respectively;When combined AITC(LC30)with LD30of beta-cypermethrin（0.12μg/cm2）and LD50 of beta-cypermethrin（0.20μg/cm2）,the synergistic toxicity index was 142.89 and 62.30,and the corrected toxicity ratio was 2.20 and 1.56,respectively.The above results showed that both of combinations of AITC with pirimiphos-methyl or beta-cypermethrin has synergistic effect.However,the combination of LC30 of AITC with LD30of beta-cypermethrin has a better synergistic effect.In conclusion,AITC has high fumigation activity against L.bostrychophila,and its combined use with pyrethroid stored grain protectants can improve the insecticidal efficacy.This combination way has good application potential in the control of booklice in the future.3.The molecular response mechanism of L.bostrychophila to different stored grain protectants and AITC was analyzedIn this study,comparative transcriptomics was used for the first time to systematically analyze the changes of gene expression at transcriptional level in L.bostrychophila under the stress of pirimiphos-methyl,beta-cypermethrin,and AITC,respectively.A total of 451 differential expression genes（DEGs）were identified under pirimiphos-methyl treatment,including 184 up-regulated genes and 267 down-regulated genes.Under beta-cypermethrin treatment,208 DEGs were identified,including 72 up-regulated genes and 136 down-regulated genes.A total of 517 DEGs were identified under AITC treatment,including 148 up-regulated genes and 369 down-regulated genes.Among the above DEGs,there are a large number of detoxification and metabolism related genes,including 32 P450 genes,8 Esterase genes（ESTs）,6 glutathione S-transferases genes（GSTs）,9 ABC transporter genes（ABCs）and 16 UDP-glucuronosyltransferases genes（UGTs）.However,there are no up-regulated and down-regulated genes in common from these three insecticide treatment transcriptomes.KEGG enrichment annotation showed that a large number of differentially expressed genes were concentrated in the drug metabolism pathway,indicating that the detoxification and metabolism related genes of L.bostrychophila play an important role in tolerance or resistance to insecticides.The results of this study suggest that different detoxification genes will respond to different insecticides,and their expression level or trend is varied inordinately.Under the stress of an insecticide,a large number of genes cooperating with each other and a variety of metabolic regulation networks will be involved in reducing the damage caused by insectcides. |
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