Host‐associated genetic differentiation in pecan leaf phylloxera

Host‐associated differentiation (HAD) is the formation of genetically distinct host‐associated populations. One of the genotypic signatures of HAD is that populations exhibit stronger differentiation by host‐plant species than by geographic isolation. HAD, as a mechanism promoting ecological speciation, has been invoked to explain phytophagous insect diversity. Two traits proposed to promote HAD are endophagy and parthenogenesis. Using amplified fragment length polymorphisms (AFLPs), we tested for the presence of HAD in pecan leaf phylloxera, Phylloxera notabilis Pergande (Hemiptera: Phylloxeridae), an endophagous, gall inducing, and cyclically parthenogenetic insect on sympatric pecan and water hickory at a geographic mesoscale. This species shows strong HAD. Whereas the effect of collecting site was significant, accounting for 7.3% of molecular variation, host‐plant species identity accounted for 63.5%. In addition, a choice test indicated that pecan leaf phylloxera originating from water hickory showed weak but significant preference for leaflets of the natal host, whereas pecan leaf phylloxera originating from pecan did not. This is the first such study of a species of arboreal Phylloxeridae, a poorly known insect group. This is also the first endophage and the second parthenogen shared by these two hickory species to show evidence of HAD. This hickory system could be a good parthenogen‐rich counterpoint to the goldenrod system in the study of HAD in insect communities.     

New Antagonistic Strains of Non‐Pathogenic Agrobacterium vitis to Control Grapevine Crown Gall

Graft unions of nursery stock of grapevine (Vitis vinifera L.) collected in Japan yielded non‐pathogenic strains of Agrobacterium. On the basis of classic diagnostic tests, a sequence analysis and a previously reported multiplex PCR method, the non‐pathogenic strains ARK‐1, ARK‐2 and ARK‐3 were identified as Agrobacterium vitis. Stems of grapevine seedlings were inoculated with both a cell suspension of seven mixed strains of A. vitis (Ti) as a pathogen and one of a new strain or A. vitis strain VAR03‐1, one of the biological control agents against crown gall previously reported, as competitors to assay the suppression of tumour formation caused by the pathogen. In a test with a 1:1 cell ratio of pathogen/nonpathogen, strains ARK‐1, ARK‐2 and ARK‐3 reduced the tumour incidence.. In particular, strain ARK‐1 was strongest at inhibiting tumour formation in this study. Strain ARK‐1 established populations on roots of grapevine tree rootstock and persisted on roots for a year. ARK‐1, ARK‐2 and ARK‐3 did not produce a halo of inhibition against A. vitis (Ti) strain on YMA medium. Moreover, strain ARK‐1 did not reduce tumour incidence on the stems of grapevine when ARK‐1 was dead or only culture filtrate was used. This result indicates the possibility that these new strains inhibit grapevine crown gall in planta by a different mechanism other than VAR03‐1. In particular, one of the new strains, named ARK‐1, was most effective in inhibiting tumour formation on grapevine and appears to be a promising new agent to control grapevine crown gall.     

刺桐姬小蜂发生习性及其虫瘿形成分析

刺桐姬小蜂Quadrastichus erythrinaeKim是新发现的重要入侵害虫,在广东省深圳地区普遍发生且危害严重,受害植株超过10000株。寄主按受害程度依次为:杂色刺桐Erythrina variegata、金脉刺桐E.variegatevar.orientialis、鸡冠刺桐E.cristagalli和龙牙花E.corallodendron。移栽2年内的刺桐树受害严重。根据虫瘿形状,将其分为球形虫瘿、卷叶形虫瘿、肥厚叶虫瘿、分散虫瘿、粗柄形虫瘿、嫩枝肿大虫瘿、花蕾肿大虫瘿并对其形成过程进行分析。首次报道了刺桐姬小蜂为害鸡冠刺桐花蕾。刺桐姬小蜂在深圳无休眠和滞育现象,常年发生。     

Mode of Action of the Antibacterial Compound Ar26 Produced by Agrobacterium vitis Strain E26 with Activity against A. tumefaciens, A. rhizogenes and A. vitis

The biological control bacterium Agrobacterium vitis strain E26 was previously shown to produce an antibacterial compound, Ar26. This compound was involved in the biocontrol process and inhibited grapevine crown gall-causing A. vitis strains in vitro by an unknown mechanism. This work was undertaken to determine the antibacterial properties and mode of action of Ar26. In a well agar plate diffusion assay against 29 tumorigenic isolates of Agrobacterium spp., Ar26 displayed broad inhibitory activity against 27. All of the 10 A. vitis , 8 of 9 A. tumefaciens and 9 of 10 A. rhizogenes strains were sensitive to this compound. Agrobacterium vitis strains were more sensitive to Ar26 than A. tumefaciens or A. rhizogenes strains, with larger inhibition zones and lower minimal inhibitory concentration (MIC). Ar26 exhibited a bactericidal effect against A. vitis. This compound did not cause bacterial cell lysis, as determined by morphological observation with an electronic microscope. Also, no leakage of cytoplasmic materials from cells of A. vitis occurred after treatment with Ar26 at concentrations equivalent to the MIC. However, an inhibition of the incorporation of radiolabelled precursors into DNA, RNA and protein was observed after treatment with Ar26. Results obtained suggest that Ar26 inhibited DNA, RNA and protein syntheses in tumorigenic A. vitis .     

Host‐race formation: promoted by phenology,constrained by heritability

Host‐race formation is promoted by genetic trade‐offs in the ability of herbivores to use alternate hosts, including trade‐offs due to differential timing of host‐plant availability. We examined the role of phenology in limiting host‐plant use in the goldenrod gall fly (Eurosta solidaginis) by determining: (1) whether phenology limits alternate host use, leading to a trade‐off that could cause divergent selection on Eurosta emergence time and (2) whether Eurosta has the genetic capacity to respond to such selection in the face of existing environmental variation. Experiments demonstrated that oviposition and gall induction on the alternate host, Solidago canadensis, were the highest on young plants, whereas the highest levels of gall induction on the normal host, Solidago gigantea, occurred on intermediate‐age plants. These findings indicate a phenological trade‐off for host‐plant use that sets up the possibility of divergent selection on emergence time. Heritability, estimated by parent–offspring regression, indicated that host‐race formation is impeded by the amount of genetic variation, relative to environmental, for emergence time.     

中华蚊母树虫瘿类型及其致瘿昆虫生活史初探

初步观察了中华蚊母树(Distylium chinense(Fr.)Diels)不同类型虫瘿的发生过程及致瘿昆虫生活史。结果表明,中华蚊母树的虫瘿有3种类型,分别为叶/枝上大型虫瘿、叶上泡状虫瘿和叶柄/果上球型虫瘿。三者均为单室封闭型,次生开口。经鉴定致瘿昆虫均为半翅目蚜科昆虫,其中叶上泡状虫瘿致瘿昆虫为蚊母新胸蚜Neothoracaphis yanonis Matsumura。该虫3月初在虫瘿内营孤雌生殖,繁殖2代,5月底前飞离出瘿。     

Dissecting the association between a gall midge,Asteromyia carbonifera,and its symbiotic fungus,Botryosphaeria dothidea

The Ambrosia gall midge [Asteromyia carbonifera (Osten Sacken) (Diptera: Cecidomyiidae: Alycaulini)] consists, in part, of a complex of genetically differentiated populations that have diverged in gall morphology on the host plant Solidago altissima L. (Asteraceae). This divergence appears to be an incipient adaptive radiation that may be driven by parasitoid pressure. Understanding the mechanisms driving this genetic and phenotypic diversification requires a close examination of the relationship between the midge and its fungal associate Botryosphaeria dothidea (Moug.) Ces. & De Not. (Ascomycota: Dothideomycetes), whose mycelia actually form the protective gall structure. We used manipulative experiments to test the degree of interdependency of the fungus and the midge, and we employed field and laboratory studies to gain insight into the source of fungal conidia, which our data and observations indicate are collected by females and stored in specialized pockets (mycangia) on the ovipositor. Manipulative experiments demonstrate that fungal proliferation on the host plant is dependent on the midge larvae and larvae exhibit significant growth on the fungus alone. Field observations and experiments were unable to identify the source of mycangial conidia; however, analyses of conidia shape suggest a biotrophic source. We conclude that this association is an obligatory mutualism with respect to successful gall formation. These findings corroborate recent findings that the primary food source of the midge is the gall fungus.     

Gall-inducing insects provide insights into plant systematic relationships

Field surveys of cynipid gall-inducer occurrences on Quercus species were conducted in Florida, North Carolina, and Pennsylvania, USA. All cynipids demonstrated strong host species and organ fidelity. One result of this specialization is effective niche partitioning among cynipids. The host-association patterns of these specialist herbivores should reflect similarities among oaks, thus we clustered oak species according to their cynipid distributions. Cynipids distinguished small differences among their hosts. A dendrogram of oak species based on cynipid distributions was largely congruent with botanical arrangernents. Cynipid occurrences offer information helpful to resolving some aspects of oak systematics. Collaborative efforts between taxonomic botanists and entomologists will be useful in resolving a variety of plant and insect systematic problems.     

Identification and quantification of brassinolide-related steroids in the insect gall and healthy tissues of the chestnut plant

Castasterone and 6-deoxocastasterone were identified by GC/MS and/or selected ion monitoring not only in the insect gall of chestnut but also in the healthy tissues, including the shoot, leaf and flower bud. In addition, the gall was found to contain a small amount of brassinolide. Brassinone, which had been reported to be present in the gall, could not be detected in these tissues. The contents of castasterone, 6-deoxocastasterone and brassinolide, which were determined by using selected ion monitoring, are discussed.