The recent emergence of several plant diseases caused by psyllid-borne bacterial pathogens worldwide (Candidatus Liberibacter spp.) has created renewed interest on the interaction between psyllids and bacteria.In spite of these efforts to understand psyllid association with bacteria,many aspects of their interactions remain poorly understood.As more organisms are studied,subtleties on the molecular interactions as well as on the effects of the bacteria on the psyllid host are being uncovered.Additionally,psyllid-borne bacterial phytopathogens can also affect the host plant,which in turn can impact psyllid physiology and behavior.Here,we review the current literature on different aspects of the influence of bacteria on multitrophic interactions among plants,psyllids,and pathogens.We then highlight gaps that need to be addressed to advance this field,which can have significant implications for controlling these newly emergent and other plant diseases.

[目的]为了让入侵植物假臭草Praxelis clematidea(Griseb)R.M.King&H.Rob.变废为宝,首次探讨了假臭草花精油对柑橘木虱Diaphorina citri Kuwayama的驱避和致死活性,以用于生物防治.[方法]采用水蒸气蒸馏法提取了假臭草不同部位的精油,并通过气相色谱-质谱联用仪(GC-MS)分析花精油的化学成分,并检测了其对柑橘木虱的生物活性.[结果]假臭草花精油得率(0.31±0.03)％高于茎叶精油的得率(0.23±0.02)％;GC-MS检测显示,假臭草花精油至少含有25种化合物,其中 β-荜澄茄油烯(43.85％)和 β-石竹烯(30.34％)是其主要成分;花精油浓度为40和50μL·mL-1处理30 min时,对柑橘木虱的驱避反应率均可达到100％.不同浓度的花精油对柑橘木虱具有明显的致死活性.当浓度为50μL·mL-1的时候,浸液法处理九里香Murraya exotica L.嫩梢18 h时,柑橘木虱校正死亡率分别达到(56.25±4.79)％,LC50值为44.83μL·mL-1,而熏蒸法48 h时的柑橘木虱校正死亡率仅为(66.33±5.00)％,LC50为24.80μL·mL-1.假臭草花精油对柑橘木虱的驱避和致死活性可能与其主要成分的作用有关.[结论]研究结果证明假臭草花精油对柑橘木虱具有良好的驱避和致死活性,具有开发成为柑橘木虱驱避剂及杀虫剂的良好潜能.

Insect herbivore outbreaks frequently occur and this may be due to factors that restrict top-down control by parasitoids,for example,host-parasitoid asynchrony,hyperparasitization,resource limitation and climate.Few studies have examined hostparasitoid density relationships during an insect herbivore outbreak in a natural ecosystem with diverse parasitoids.We studied parasitization patterns of Cardiaspina psyllids during an outbreak in a Eucalyptus woodland.First,we established the trophic roles of the parasitoids through a species-specific multiplex PCR approach on mummies from which parasitoids emerged.Then,we assessed host-parasitoid density relationships across three spatial scales (leaf,tree and site) over one year.We detected four endoparasitoid species of the family Encyrtidae (Hymenoptera);two primary parasitoid and one heteronomous hyperparasitoid Psyllaephagus species (the latter with female development as a primary parasitoid and male development as a hyperparasitoid),and the hyperparasitoid Coccidoctonuspsyllae.Parasitoid development was host-synchronized,although synchrony between sites appeared constrained during winter (due to temperature differences).Parasitization was predominantly driven by one primary parasitoid species and was mostly inversely host-density dependent across the spatial scales.Hyperparasitization by C.psyllae was psyllid-density dependent at the site scale,however,this only impacted the rarer primary parasitoid.High larval parasitoid mortality due to density-dependent nymphal psyllid mortality (a consequence of resource limitation) compounded by a summer heat wave was incorporated in the assessment and resulted in density independence of host-parasitoid relationships.As such,high larval parasitoid mortality during insect herbivore outbreaks may contribute to the absence of host density-dependent parasitization during outbreak events.

Two parasitoids attacking nymphs of Asian citrus psyllid,Diaphorina citri Kuwayama (Hemiptera:Liviidae),Tamarixia radiata (Waterston) (Hymenoptera:Eulophidae) and Diaphorencyrtus aligarhensis (Shafee,Alam & Agarwal) (Hymenoptera:Encyrtidae) are being released in California,USA in a classical biological control program.To evaluate the effect of multiple parasitoid species on D.citri mortality,we conducted mesocosm experiments under controlled conditions using a complete block design with 6 treatments (D.citri nymphs exposed to:no parasitoids;D.aligarhensis or T.radiata alone;D.aligarhensis or T.radiata released first (by 48 h);and both species released simultaneously).Parasitism of D.citri nymphs by T.radiata exceeded 60％ and was unchanged when D.aligarhensis were present.Parasitism by D.aligarhensis was greatest when T.radiata was absent (～28％) and was reduced in all treatments with T.radiata present (＜3％).D.citri mortality and parasitoid-related mortality ofD.citri was consistent across parasitoid treatments.Laboratory results suggest that competition between D.aligarhensis and T.radiata is asymmetric and favors T.radiata.It may be difficult for D.aligarhensis to contribute significantly to D.citri biological control where T.radiata is present.However,results reported here suggest that competition between T.radiata and D.aligarhensis is not likely to reduce parasitism by T.radiata or reduce parasitoid-induced mortality of D.citri.

Wolbachia can profoundly influence the survival,reproduction,and defenses of insect hosts.These interactions could potentially be harnessed for managing pests or insecttransmitted diseases.Diaphorina citri Kuwayama is a phloem-feeding pest capable of transmitting the putative causal agent of citrus greening,Candidatus Liberibacter asiaticus (CLas).Like many insects,D.citri is also infected with Wolbachia (wDi).Recent studies indicate that the relative abundance of wDi could be associated with the abundance of CLas,and that wDi may contribute to regulating expression of phage lytic cycle genes in CLas,suggesting the need for better understanding of wDi biology in general.This study investigated the genetic diversity of wDi among D.citri in populations spanning eleven countries and two U.S.territories.Six Wolbachia genes,wsp,coxA,fbpA,ftsZ,gatB,and hcpA,were sequenced and compared across samples.Two prevalent wDi strains were identified across the samples,and screening of clone libraries revealed possible coinfection of wDi strains in specific populations.D.cirri mitochondrial cytochrome oxidase subunit Ⅰ gene (mtCOI) were more divergent between D.citri populations that were infected with different wDi strains or had different infection statuses (single infection vs.coinfection).While we could not eliminate the possibility that maternal transmission may contribute to such patterns,it is also possible that wDi may induce cytoplasmic incompatibility in their host.These findings should contribute to the understanding of wDi population ecology,which may facilitate manipulation of this endosymbiont for management of citrus greening disease worldwide.

The Asian citrus psyllid (Diaphorina citri Kuwayama) is known to exhibit abdominal color polymorphisms.In the current study,susceptibility to four insecticides was compared among orange/yellow,blue/green and gray/brown color morphs of field collected D.citri.The LD50 values and 95％ fiducial limits were quantified for each insecticide and color morph combination and ranged between 0.10 ng/μL (0.06-0.10) and 6.16 ng/μL (3.30-12.50).Second,we measured the detoxification enzyme activity levels of orange/yellow,blue/green and gray/brown color morphs for cytochrome P450,glutathione S-transferase,and general esterase.The mean P450 activity (equivalent units) was significantly lower in gray/brown (0.152 ± 0.006) and blue/green morphs (0.149 ± 0.005) than in the orange/yellow morphs (0.179 ± 0.008).GST activity (μmol/min/mg protein) was significantly lower in the orange/yellow morph (299.70 ±1.24) than gray/brown (350.86 ± 1.19) and blue/green (412.25 ± 1.37) morphs.The mean EST activity (μmol/min/mg protein) was significantly higher in blue/green (416.72 ± 5.12) and gray/brown morphs (362.19 ± 4.69) than in the orange/yellow morphs (282.56 ± 2.93).Additionally,we analyzed the relative expression of assortment genes involved in cuticular melanization and basal immunity.The transcripts of Dopa Decarboxylase and Tyrosine Hydroxylase were expressed higher in blue/green and gray/brown than orange/yellow morphs.The transcription results paralleled the susceptibility of D.citri to organophosphate,neonicotinoid and pyrethroid insecticides.GST and EST activity may also be correlated with low levels of insecticide susceptibility.Cuticular melanization could be a factor for the development of resistance to insecticides among different color morphs.

黄龙病是全球广泛发生的毁灭性病害,柑橘木虱为其主要媒介昆虫.越南最早于上个世纪六十年代有相关报道.通过一些国际合作项目,越南对柑橘木虱和黄龙病进行了一系列研究并积极采取措施有效防控:包括消除病株、筛选抗病虫品种、改变种植密度和时间、化学防治与生物防治、作物间种、喷施矿物油乳剂、施用有机肥、使用无病苗和无病接穗并在运输过程中封闭保护等.其中控制黑臭蚁Dolichoderus thoracicus增殖黄猄蚁Oecophylla smaragdina、交错式间种番石榴以控制柑橘木虱和黄龙病值得中国借鉴和参考.

Bacillus thuringiensis (Bt) toxins are effective in controlling insect pests either through the spraying of products or when expressed in transgenic crops.The discovery of endophytic Bt strains opened new perspectives for studies aimed at the control of sapsucking insects,such as the Asian citrus psyllid Diaphorina citri Kuwayama (Hemiptera:Liviidae),a vector of"Candidatus Liberibacter spp.," associated with citrus huanglongbing (HLB).In this study,transloeation of endophytic Bt strains in citrus seedlings inoculated with Bt suspension delivered by soil-drench,and their systemic pathogenicity to D.citri nymphs were investigated.The pathogenicity of three wild-type Bt strains against D.citri third-instar nymphs was demonstrated.Among the 10 recombinant strains tested (each of them harboring a single cry or cyt gene),3 can be highlighted,causing 42％-77％ and 66％-90％ nymphal mortality at 2 and 5 d after inoculation,respectively.The isolation of Bt cells from young citrus shoots and dead nymphs,and PCR performed with specific primers,confirmed the involvement of the Bt strains in the psyllid mortality.This is the first report showing the translocation of Bt strains from citrus seedling roots to shoots and their potential to control D.citri nymphs that fed on these soil-drench inoculated seedlings.The Bt strains that caused the highest mortality rates have the potential to be used as bioinsecticides to control D.citri and the identified genes can be used for the production of transgenic Bt citrus.

Immunofluorescence has been widely used to localize microbes or specific molecules in insect tissues or cells.However,significant autofluorescence is frequently observed in tissues which can interfere with the fluorescent identification of target antigens,leading to inaccurate or even false positive fluorescent labeling.The alimentary canal of the potato psyllid,Bactericera cockerelli (S)ulc,exhibits intense autofluorescence,hindering the application of immunolocalization for the detection and localization of the economically important pathogen transmitted by this insect,"Candidatus Liberibacter solanacearum" (Lso).In the present study,we tested the use of irradiation,hydrogen peroxide (H2O2) and Sudan black B (SBB) treatments to reduce the autofluorescence in the B.cockerelli alimentary canal tissues.Furthermore,we assessed the compatibility of the above-mentioned treatments with Lso immunolocalization and actin staining using phalloidin.Our results showed that the autofluorescence in the alimentary canal was reduced by irradiation,H2O2,or SBB treatments.The compatibility assays indicated that irradiation and H2O2 treatment both greatly reduced the fluorescent signal associated with Lso and actin.However,the SBB incubation preserved those target signals,while efficiently eliminating autofluorescence in the psyllid alimentary canal.Therefore,herein we propose a robust method for reducing the autofluorescence in the B.cockerelli alimentary canal with SBB treatment,which may improve the use of immunofluorescence labeling in this organism.This method may also have a wide range of uses by reducing the autofluorescence in other arthropod species.

The potato/tomato psyllid Bactericera cockerelli causes serious damage to several solanaceous crops by direct feeding and vectoring Candidatus Libedbacter solanacearum,a bacterial pathogen.Electron beam (eBeam) irradiation is an environmentally friendly,chemical-free alternative method that is increasing in use for disinfestation of insect pests.We hypothesize that this irradiation technology will have detrimental effects on potato psyllid and thus impede its disease vectoring.To this end,we explored the effects of eBeam treatment ranging from 50 to 500 Gy on survival,development and reproduction of this pest.Impact on psyllids was apparently dose-dependent.When irradiated at 350 Gy,eggs could not hatch,1st instar nymphs failed to emerge,and although a small portion of irradiated 5th instar nymphs survived,the emerged adults were mostly deformed.Abnormality in eclosed adults suggests harmful effects of eBeam on metamorphosis.Reproduction was seriously impaired when female psyllids were exposed to eBeam at the 5th instar nymphal or young adult stage,presumably due to inability to form oocytes.In addition,reciprocal crosses between irradiated and untreated psyllids indicated that female psyllids were more radiosensitive than males to eBeam.Taken together,these findings indicate that eBeam negatively impacted potato psyllid development and reproduction,which would inevitably compromise its disease transmission capacity.A dose of 350 Gy can be considered as a reference dose for effective control of potato psyllids.