| The Eucalyptus gall wasp, Leptocybe invasa, is one of the most devastating pests, whichcauses severe injury to young foliage of Eucalyptus spp. Since its first recorded occurrence inChina in2007, the pest had caused serious damage to the eucalypt plantation resource in thiscountry. Based on investigations and studies of the biological and ecological characteristics of thepest in Fujian, this paper provides detailed analysis regarding host preference, oviposition taxis,resistance among eucalypt taxa and the relationship between some physio-biochemical indices inleaves of different species and plant resistance. Further research into chemical defense of E.grandis by different induced treatments, which included by gall wasp oviposition, physicaldamage and exogenous methyl jasmonate （MeJA）, was carried out. Result analysed includedtemporal changes of chemical substances in leaves. From the aspects of nutrients, secondarymetabolites, defense enzymes, protease inhibitors and plant volatiles, we investigated themechanisms involved in chemical defenses of E. grandis and the effects of these changes on thegrowth, development and population trend of L. invasa. This research revealed interactionsbetween the pest infestation and chemical defense of Eucalyptus species, and provided newinsights for technical approaches to control the pest by breeding insect-resistant species andimproving host defense capability. After three years of research, the major results obtained are asfollows:1. The harm status and levels of damage to different varieties caused by L. invasa weresurveyed in Fujian. Results showed:（1） Most of the infested eucalypt varieties can attacked by L.invasa in Fujian; when the larvae feed on E. urophylla×E. camaldulensis clone DH201-2, E.gradis clone QG3, E. dunnii, E. urophylla clone U6, E. grandis×E. urophylla clone GL9, E.robusta and E. exserta respectively, they can form galls, grow normally and complete their lifecycle.（2） There were differences among varieties for the degree of damage and host fitness of L.invasa, which resulted in changes to frequency through selection, and the fecundity and number oflarvae on differ among different Eucalyptus varieties.（3） L. invasa larvae fed by differentEucalyptus varieties, aside from the female ratio, differed significantly in other attributesincluding emergence rate, female weight, fecundity and longevity of female.（4） According to thefitness index （FI）, the host plants of L. invasa were divided into4categories by cluster analysis:the most suitable, suitable, secondary and unsuitable. Fed on suitable host, fecundity reaches morethan70eggs per female which is adequate to lead to potential population explosion of the pest.We can use host fitness index as a comprehensive evaluation index for the screening of resistant clones in practice.2. The effects of smell and color of different Eucalyptus varieties on host preference by L.invasa were studied in laboratory. In addition, selection behavior of oviposition of the pest wasstudied in the field. The results revealed that:（1） There were significant differences amongeucalypt species for female adult preference by smell–out of10Eucalyptus varieties femaleadults showed the strongest preference for E. urophylla×E. camaldulensis clone DH201-2.However, the pest had negative taxis or no selection for either E. wetarensis×E.camaldulensisclone GL3or E. cloeziana.（2） Color tests showed that there were obvious differences amongcolor cards for their pest-attracting effect, pure white cards （RAL9010） and signal yellow cards（RAL1003） had an obvious attraction effect, with the selection coefficients accounting for0.29and0.28respectively.（3） The analyzed results showed that the number of oviposition scars weresignificantly different among Eucalyptus varieties. It is obvious that the oviposition scars on E.urophylla×E. camaldulensis clone DH201-2were more than other varieties.3. In order to investigate relationships between L. invasa and different Eucalyptus varietiesand to examine the change process of the host stress response after being damaged, we screened13infested eucalypt clones and species in Fujian and graded these for resistance, then measuredthe contents of water, nutrients and secondary substances in young foliage of these differentvarieties. Data obtained from this work was analyzed by the grey relational analysis. The resultsshowed that:（1）13varieties showed resistance, including E. urophylla×E. grandis clonesDH32-28and, DH32-26, E. grandis×E. urophylla clone GL3, E. urophylla×E. tereticornisclone M1, E. grandis clone JG1, E. cloeziana and E. saligna. All other varieties screened haddifferent degrees of susceptibility. The research also showed that the resistance of different clonesfrom same species differed significantly.（2） The number of galls per sample branchlet and thenumber of wasp larvae per gall differed greatly among varieties.（3） The water content in youngfoliage of different varieties differed greatly, with susceptible varieties having much lower foliagewater contents than did resistant varieties. As the level of resistance increased, the contents ofsoluble sugars, polysaccharides and proteins in young foliage decreased, whilst the content offlavonoids, tannins and total phenols increased.（4） Grey relational analysis between contents ofnutrients and secondary substances in young foliage of different varieties and damage degrees bythe gall wasp, showed that the content of nutrients, especially the content of polysaccharide, hadgreater impact on the growth of the wasp and varieties resistance than did other attributesmeasured.4. Chemical analysis of some chemical substances in leave and volatiles emitted from E.grandis after inductions by gall wasp oviposition, physical damage and exogenous MeJA was studied. The results showed that:（1） Induction treatments can all induce changes in the nutrientcontent of Eucalyptus leaves, including contents of soluble sugars, polysaccharides and proteins.Compared with the control group, the content of these compounds tended to decline. But, theintensity of defense reaction caused by MeJA treatment was higher.（2） In regard to three methodsof induction, compared with the control group, the content of secondary metabolites, such asflavones, tannins and total phenols, all had obvious tendencies to increase, and the contents of allkinds of secondary metabolites showed different results over time.（3） Variation in the activitylevels of PAL、SOD、POD and PPO enzymes in Eucalyptus leaves showed some correlations withdifferent induction treatments, indicating that different methods of induction had differing effectson the activity of protective enzymes. Generally speaking, enzymatic activity induced by insectattack and MeJA treatment was more obvious than physical damage.（4） Different inductiontreatments can all stimulate change to the activity of TI and CI in eucalyptus leaves, moreover,different treatments had different results over time. Induced by MeJA, compared with physicaldamage, increased the amplitude of TI and CI activities in Eucalyptus leaves–the amplitude washigher and peaked quicker–which was similar to the change caused by insect attack.（5） VOCsof E. grandis were studied by the methods of headspace enrichment and GC-MS in this paper. Theresults showed that the composition and quantity of the VOCs were significantly different amongthe four treatments. After different inductions, terpene volatiles emitted largely in1-3days, butthe volatile emissions decreased gradually after5-7days.5. Through different induction treatments, changes on physiological and biochemical indicesof Eucalyptus leaves were studied, along with the effects on indices of the growth, development,reproductive activity and population trends of L. invasa. The results showed that:（1） Plants withinduction treatments that were inoculated with L. invasa, revealed that the survival rate ofoffsprings of L. invasa decreased, average weight of females declined, fecundity reduced, averagelife span shortened, and the index of population trend decreased.（2） Vague comparative methodon similarity evolution between oviposition-induction and other induction treatments, showed thatspraying1.0mmol·L-1MeJA can make the similar result as oviposition, demonstrated sprayingMeJA plays an active role in induced resistance, which can be used as the supplementary methodfor integrated pest management. |
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