Interactive effects of mycorrhizal fungi,salt stress,and competition on the herbivores of Baccharis halimifolia

1. Plant stress and association with mycorrhizal fungi have been shown to significantly influence plant quality, yet their roles in influencing plant–insect interactions remain unclear. Even less is known about how these factors might interact with or be modified by within‐trophic level interactions. 2. In the present study, the results of a factorial field experiment are reported in which the effects of within‐trophic‐level interactions, plant stress, and mycorrhizae on three herbivores of Baccharis halimifolia were examined. 3. Plant stress was increased by adding salt to the soil, and availability of mycorrhizal fungi was increased by inoculating plant roots. These treatments were applied to plants with either low or high densities of a competitor (Trirhabda baccharidis). 4. For the two leaf miners, Amauromyza maculosa and Liriomyza trifolii, increased soil salinity and high densities of the competitor Trirhabdabaccharidis resulted in significant decreases in density. Neither of these treatments affected the gall maker Neolasioptera lathami. 5. Mycorrhizal fungi increased the densities of all three herbivores, possibly by increasing foliar nitrogen levels. For the two leaf miners, there was also evidence that mycorrhizae ameliorated the negative effects of salt stress. There was also evidence that high levels of competition dampened the positive effects of mycorrhizae on the two leaf miners.     

Time tells: long-term patterns in the population dynamics of the yew gall midge, Taxomyia taxi (Cecidomyiidae), over 35 years

Abstract. 1. Three populations of the yew gall midge, Taxomyia taxi, and its two chalcid parasitoids, Mesopolobus diffinis and Torymus nigritarsus, from Kingley Vale, West Sussex, U.K., were monitored each year between 1966 and 2002. Taxomyia taxi's life cycles are either hemivoltine or univoltine and the parasitoids' are univoltine (T. nigritarsus) or multivoltine (M. diffinis). 2. Growth of the host trees, yew Taxus baccata, each year between 1950 and 1997 was assessed by width of annual rings in cores taken in 1998. Temperature and rainfall data were provided by the weather station in Southampton, representative of the climate of central southern England. 3. Time‐series analyses were conducted to explore the effects of climate, tree growth, and parasitoids on each T. taxi population and on the three populations combined. Four time‐delayed models were developed: for hemivoltine and univoltine T. taxi and for each of the parasitoids. 4. Hemivoltine T. taxi populations showed troughs in density in the periods 1972–1975 and 1991–1992, which were more pronounced in even than odd years; these were closely tracked by M. diffinis and followed, after a delay, by T. nigritarsus. Time‐series models showed that, for T. taxi, its current density depended on the density of its hemivoltine parents moderated by the negative effects of T. nigritarsus on these parents. In reciprocal fashion, T. nigritarsus density was influenced by that of its hemivoltine host as well as by its own previous density. Host and parasitoid appear to participate in a coupled interaction that regulates the populations of both via delayed density dependence, resulting in cycles of at least 14 years. Mesopolobus diffinis had no effect on the dynamics of hemivoltine T. taxi, most of which escaped its parasitism. Although univoltine T. taxi can give rise to hemivoltine offspring, there was no evidence that they affected hemivoltine dynamics. 5. The density of univoltine T. taxi was usually much lower than hemivoltine density and varied irregularly over time. It was not attacked by T. nigritarsus but parasitism by M. diffinis was always high. Despite this, its density depended only on the density of its parents, especially the hemivoltine parents. Parasitism had no effect on the dynamics of univoltine T. taxi. Conversely, M. diffinis density depended solely on the densities of both univoltine and hemivoltine hosts. 6. Tree growth appeared to have little effect on the dynamics of the host or parasitoids and there was no evidence that gall density had any effect on growth of the tree. The primary effect of climate appeared to be in maintaining the cyclic nature of the T. taxi–T. nigritarsus interaction. If stochastic weather variables are removed from the models, the oscillations are of equivalent periodicity but dampen to equilibrium.     

The life history of a gall‐inducing mite: summer phenology,predation and influence of gall morphology in a sugar maple canopy

• 1 Eriophyoid mites are among the most ubiquitous gall‐inducing arthropods, and are adapted species‐specifically to a broad diversity of plants, although their life histories remain poorly studied outside agricultural systems.
• 2 We examined the seasonal phenology of a leaf‐galling eriophyid mite, the maple spindle gall mite Vasates aceriscrumena (MSGM), in naturally occurring stands of sugar maple Acer saccharum in south‐central Ontario in 2007 and 2008.
• 3 Galls were first induced in spring (mid‐May) and were devoid of mites by late August. In the study region, MSGM appears to have at least two generations, with overwintering, deutogyne females that initiate galls in spring (mid‐May) after leaf flush, giving rise to a generation of protogyne (primary) females and a few morphologically similar males (<1 for every 10 females) and, subsequently, to a new generation of deutogyne females in mid‐July to early August. In July, some galls can be highly crowded, with 50–200 individuals per gall.
• 4 In addition, a tarsonemid mite, Tarsonemus acerbilis, was found in approximately 40% of MSGM galls examined. As much as 95.4% of galls in 2007 and 97.4% in 2008 that contained tarsonemid larvae did not contain MSGM eggs (by contrast, only 2.3% of tarsonemid‐free galls contained no MSGM eggs), suggesting that these juveniles feed, at least opportunistically, on MSGM eggs.
• 5 Gall ostiole morphology appeared to influence both MSGM and Tarsonemus densities within galls, with ‘open’ ostioles (versus ‘closed’) being much more susceptible to invasion by the tarsonemid. The latter is likely to be an important regulator of MSGM populations. We hypothesize that the two ostiole types are the result of selection pressures on the gall inducer, favouring closed gall entrances for increased protection, and possibly also on the host tree, favouring open galls to increase predator access.

     

Transcapsidation and the conserved interactions of two major structural proteins of a pair of phytoreoviruses confirm the mechanism of assembly of the outer capsid layer

The strongly conserved amino acid sequences of the P8 outer capsid proteins of Rice dwarf virus (RDV) and Rice gall dwarf virus (RGDV) and the distribution of electrostatic potential on the proteins at the interfaces between structural proteins suggested the possibility that P8-trimers of RGDV might bind to the 3-fold symmetrical axes of RDV core particles, with vertical interaction between heterologous P3 and P8 proteins and lateral binding of homologous P8 proteins, thereby allowing formation of the double-layered capsids that are characteristic of viruses that belong to the family Reoviridae. We proved this hypothesis using chimeric virus-like particles composed of the P3 core capsid protein of RDV and the P8 outer capsid protein of RGDV, which were co-expressed in a baculovirus expression system. This is the first report on the molecular biological proof of the mechanism of the assembly of the double-layered capsids with disparate icosahedral lattices.     

高产细菌素菌株WJ K84-1的诱变筛选及其对植物病原菌抑菌机理的研究

以发根土壤杆菌K84为供试菌株,对其进行紫外诱变,采用定向竞争选择技术,筛选出高产细菌素的目的菌株WJK84-1,并对根癌农杆菌的抑菌作用及其抑菌机理进行了研究。通过琼脂扩散法和液体培养法测试表明,WJK84-1菌株和其产生的P-2001细菌素均对C58病原菌有明显的抑制作用。蛋白电泳谱带分析示出,细菌素对C58病原菌的作用是抑制蛋白合成,使其蛋白总量表达水平呈下降趋势,尤其是大分子量蛋白含量下降显著,有的蛋白谱带(R1、R4)缺失,且随细菌素浓度的增加,抑制作用更加强烈。扫描电镜观察,细菌素作用后的菌体不同部位出现缢痕,直至缢缩成颗粒状残体而死亡。透射电镜观察进一步证明,C58菌细胞膜被裂解,细胞结构被破坏而致死。樱桃接瘤实验表明,WJK84-1菌株和其产生细菌素均可抑制根瘤发生,抑瘤率达到83．4％左右。     

Detection of an invasive gall-inducing pest, Quadrastichus erythrinae (Hymenoptera: Eulophidae), causing damage to Erythrina variegata L. (Fabaceae) in Okinawa Prefecture, Japan

In 2005, Quadrastichus erythrinae Kim, 2004 (Hymenoptera: Eulophidae), which induces stem, petiole, and leaf galls on Erythrina variegata L. (Fabaceae), was found on the following six islands in Okinawa Prefecture, Japan: Okinawa, Kume, Miyako, Ishigaki, Iriomote, and Hateruma. Galls were also found in Vietnam. In Japan, no further infestation records have been reported from any of Japan's other south‐western prefectures where Erythrina species grow. Because no Erythrina galls were observed in Okinawa Prefecture before 2005, Q. erythrinae seems to have invaded quite recently.     

Evolution of gall morphology and host-plant relationships in willow-feeding sawflies (Hymenoptera: Tenthredinidae)

Abstract.— There are over 200 species of nematine sawflies that induce galls on willows (Salix spp.). Most of the species are monoor oligophagous, and they can be separated into seven or eight different groups based on the type of gall that they induce. We studied the evolution of different gall types and host plant associations by reconstructing the phylogeny of five outgroup and 31 ingroup species using DNA sequence data from the mitochondrial cytochrome b gene. Maximum-parsimony and maximum-likelihood analyses resulted in essentially the same phylogeny with high support for important branches. The results show that: (1) the galling species probably form a monophyletic group; (2) true closed galls evolved only once, via leaf folders; (3) with the possible exception of leaf rollers, all gall type groups are mono- or paraphyletic; (4) similar gall types are closer on the phylogeny than would be expected by a random process; (5) there is an apparent evolutionary trend in galling site from the leaf edge towards the more central parts of the host plant; and (6) many willow species have been colonized several times, which excludes the possiblity of parallel cladogenesis between willows and the gallers; however, there are signs of restrictions in the evolution of host use. Many of the patterns in the evolutionary history of nematine gallers have also been observed in earlier studies on other insect gallers, indicating convergent evolution between the independent radiations.     

Sequence Analysis of Segment 8 of Five Chinese Isolates of Rice Gall Dwarf Virus and Expression of a Main Outer Capsid Protein in Escherichia coli

The rice gall dwarf disease, caused by the Rice gall dwarf virus (RGDV) is a serious disease occurring in rice in many regions of Guangdong province. As a basis to control the disease we have studied the genomic diversity of a variety of isolates from different locations. Genome segment 8(S8), encoding a main outer capsid protein (Pns8) of RGDV five isolates (BL, CH, DQ, GZ, XY) from Guangdong province was cloned and sequenced. The results revealed that all the S8 segments of the five isolates consisted of 1 578 nucleotides and had a single open reading frame (ORF) extending for 1 301 nucleotides from nucleotide 21 which encoded a polypeptide of 426 amino acids with an estimated molecular weight of 47.4 kDa. The S8 full-length sequence and the ORF sequence shared 97.3%-98.8% and 97.3%-99.1% nucleotide sequence identities within the five Chinese isolates, and shared 94.8%-95.6% and 95.0%-96.0% identities with those of the Thailand isolate respectively. The deduced amino acid sequence of Pns8 in GZ isolate was identical to that in the Thailand isolate, while the amino acid sequence variability of Pns8 within five Chinese isolates ranged from 0.5% to 2.1%. These results indicate that the S8 segment of RGDV is highly conserved in different isolates from different locations. The S8 cDNA from the XY isolate was cloned into the plasmid vector pET-28b( ) and a fused expression protein with an apparent molecular mass of 51kDa was specifically detected in an analysis of Escherichia coli Rossetta(DE3)Ⅱcells. To our knowledge, this is the first report on analysis of the RGDV segment 8 sequence and genetic comparison of different RGDV isolates and their protein expression.     

Eutreta xanthochaeta (Diptera: Tephritidae) is unsuitable for biocontrol of Lantana camara in Africa

The stem-galling fly, Eutreta xanthochaeta, was evaluated as a potential agent for biocontrol of the invasive alien plant, Lantana camara, in Africa. Multi-choice trials showed an approximately equal oviposition preference for indigenous Lantana and Lippia species, and the target weed. They were also found to be about equally suitable for fly development. Finally, population sustainability studies indicated that the fly has about as much potential to persist on these indigenous plants as on the target weed. It was concluded that E. xanthochaeta is insufficiently host specific to use for biocontrol of L. camara in Africa.