| The Asian citrus psyllid,Diaphorina citri Kuwayama(Hemiptera: Liviidae)is the most important pest in the global citrus production.D.citri is a vector of the phloem-limited bacterium,‘Candidatus Liberibacter asiaticus’,which is associated with citrus huanglongbing(HLB,citrus greening disease).For the pathogenic mechanisms of huanglongbing are still not fully clarified,and the pathogen is difficult to cultivate artificially,there is no effective methods to control this disease at present.The tight control of D.citri in a large area is still the key measure to suppress huanglongbing.At present,the recognized control strategy of D.citri mainly depends on the frequent and large-scale application of pesticides.However,the long-term use of chemical pesticides causes environmental pollution by pesticide residues,and endangers human health,directly or indirectly.Meanwhile,it causes a rampant growth of secondary pests,and the resistance of D.citri is becoming more and more prominent.This dissertation was based on the theory of landscape ecology and the compound planting system of citrus,and it aimed at reducing the use of chemical pesticides,improving the ecological environment of citrus orchard,enhancing the ability of the citrus orchard to control pests and diseases.A series of studies have been done on the control of D.citri and huanglongbing including weed configuration in orchard,narrow-spectrum light source traps and pull-push combination,and application of parasitic mites.The major findings are as follows.1.The effect of weeds on the development of D.citri population and the transmission of huanglongbing(1)The adaptability of D.citri adults to these three weeds was different from each other.The D.citri adults had the strongest preference for Solanum nigrum,and the first selection rate of the selection tests was 49.80%,which was significantly higher than the other two weeds.The adults had a long survival period of up to 41 days on S.nigrum,and the females longer than the males.The D.citri adults were initially less selective for Ageratum conyzoides,but over time,the selectivity increased significantly from 28.59% to33.76%.The survival time of the D.citri adults was the longest(up to 48 days)when lived on A.conyzoides,but there was no difference between males and females.D.citri had a weak selection for Praxelis clematidea,and the survival period on it was also very short(only 11 days),and there was no difference in the survival ability of the males and females.(2)The results of the interference test of A.conyzoides on pesticides against D.citri showed that there was no significant difference in the mortality rate of D.citri adults in the first survey between the treatment group(with A.conyzoides)and the control group(without A.conyzoides),while the results of the subsequent nine surveys were significantly different.(3)The effects of the three weeds on the CLas titer in D.citri adults.In the autumn test,the CLas titer in D.citri adults significantly increased after feeding on weeds,but there was no change on Citrus reticulata.However,the results of the spring test were just the opposite.In the field investigation,the leaves of S.nigrum collected from the incidence orchard with huanglongbing,were tested by q PCR,and the results showed that there were two out of three samples to be positive.⑷The metabolites of C.reticulata,A.conyzoides and P.clematidea after different treatments,including feeding by non-infected and CLas-infected D.citri,and with no feeding as control.The results showed that there were large differences in metabolites in three plants after treatment.For the C.reticulata samples,there were 63 different metabolites after feeding by non-infected D.citri,of which the most up-regulated compounds were glycoside,and the most down-regulated phosphor esters compounds.While there were 40 different metabolites after feeding by infected D.citri,of which the up-regulated compounds,mainly were the polyphenols and coumarins.Among the A.conyzoides samples,there were 37 different metabolites after feeding by non-infected D.citri,which the main up-regulation were flavonoids,and the most important change on down-regulated compounds was mainly glycosides.While there were 51 different metabolites after feeding by infected D.citri,of which the most up-regulated compounds were aminoacids and flavonoids,and the most down-regulated chemicals were glycosidic compounds.For the P.clematidea samples,there were 52 different metabolites after feeding by non-infected D.citri,which the main up-regulated were phosphorus esters,and other compounds,such as amino acids and unsaturated acids,and the down-regulated compounds were mainly glycosides.While there were 64 different metabolites after feeding by infected D.citri,of which the most up-regulated compounds were glycosides and plant-derived insecticide rotenone,and the most down-regulated changes were amino acid compounds.The compounds from different plant types varied greatly,and the expression differences of the metabolites under different feeding stress were also quite significant.2.The application of ectoparasitic mite,Pyemotes zhonghuajia,in the biological control of D.citriThe control effect of Pyemotes zhonghuajia on D.citri was tested in this dissertation,and the results showed that there was a higher mortality rate of the D.citri adults after mite introducing in a short period of time.After two days,the mortality rate was 63.61%,and four days later,it went up to 98.06%.Compared with the control,the difference was significant.3.The trapping effect of combination of monochromdsatic light source and mineral oil on D.citriThe trapping effect of 17 different wavelengths of monochromatic light source with the same illumination intensity and their combinations on the D.citri adults was investigated in the laboratory.The results showed that the single wavelength 368 nm yellow light had the best attractant to the insects,and the trap rate was up to 48.33%,which was higher than others.The trapping rate of the push-pull combination(the light source as bait and mineral oil as repellent)was 58.67%,which was significantly higher than the use of trap light or mineral oil alone.The reduction rate of the insects was up to 100% by using push-pull combination,while less than 90% when using the other treatments.In addition,we also found that the trap rate of using combined light source,340 nm +545 nm,was significantly higher than that of using the same wavelength source alone in other experiments.Huanglongbing disease involves bacteria,vector insects,their host,non-host plants and other ecological factors,and these factors are of great importance for the effective prevention and control of huanglongbing.Ecological control technologies,including improving the configuration of orchards and nearby non-host plants,using specific narrow-spectrum light sources and their combinations,and introducing ectoparasitic mites into the orchard to control of D.citri would be beneficial for the mitigation of huanglongbing. |
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