Sequence data reflect the introduction pathways of the Sirex woodwasp parasitoid,Ibalia leucospoides (Ibaliidae,Hymenoptera)

1. The parasitoid wasp Ibalia leucospoides is native to the northern hemisphere and has been introduced to the southern hemisphere as a biological control agent for the invasive woodwasp Sirex noctilio. Two subspecies of the parasitoid, Ibalia leucospoides leucospoides (Palearctic distribution) and Ibalia leucospoides ensiger (Nearctic distribution), were introduced and are reported to have hybridized.
2. Despite extensive records of the numbers and origins of the wasps imported into the southern hemisphere, nothing is known regarding their current population diversity. We investigated the genetic variation of I. leucospoides in its native and introduced ranges using mitochondrial (COI) and nuclear (ITS) markers.
3. Mitochondrial DNA diversity in the introduced range was limited, with only five haplotypes, although sequence divergence between these haplotypes was high. Similarly, the ITS rDNA sequences revealed multiple clades present in the introduced range.
4. These results reflect introductions from a wide geographical range but where genetic bottlenecks have possibly reduced the genetic diversity. The data further reflect the origin of the I. leucospoides populations in South America and South Africa from New Zealand or Australia. We found no evidence of hybridization between the two subspecies of the parasitoid in its introduced range, and no evidence that I. leucospoides ensiger has established outside its native range.

     

Chemotactic responses of the ladybeetle Harmonia axyridis (Coleoptera: Coccinellidae) to volatile compounds from the scale insect Drosicha corpulenta (Hemiptera: Coccoidea: Monophlebidae) and its host plant

The ladybeetle Harmonia axyridis Pallas (Coleoptera: Coccinellidae), is a key predator of the scale insect Drosicha corpulenta (Kuwana), (Hemiptera: Coccoidea: Monophlebidae) in persimmon tree orchards. We used a Y-tube olfactometer and gas chromatograph/mass spectrometry to assess the possible role of volatiles from persimmon trees in attracting H. axyridis. The results showed more ladybeetles aggregated at odour sources from heavily damaged trees than from slightly damaged or undamaged trees. The relative amounts and types of terpenoid and alcohol compounds changed, usually increased, in the volatiles from damaged persimmon trees: α-pinene increased from 26 to 43%. The ladybeetle was attracted to α-pinene in a Y-tube assay at most tested concentrations.     

Fungal diversity increases soil fungistasis and resistance to microbial invasion by a non resident species

Biodiversity decline is a major concern for ecosystem functioning. Recent research efforts have been mostly focused on terrestrial plants, while, despite their importance in both natural and artificial ecosystems, little is known about soil microbial communities. This work aims at investigating the effects of fungal species richness on soil invasion by non resident microbes. Synthetic fungal communities with a species diversity ranging from 1 to 8 were assembled in laboratory microcosms and used in three factorial experiments to assess the effect of diversity on soil fungistasis, microbial invasion of soil amended with plant litter and of plant rhizosphere. The capability of different microbes to colonize environments characterized by different resident microbial communities was measured. The number of microbial species in the microcosms positively affected soil fungistasis that was also induced more rapidly in presence of synthetic communities with more species. Moreover, the increase of resident fungal diversity dramatically reduced the invasibility of both soil and plant rhizosphere. We found lower variability of soil fungistasis and invasibility in microcosms with higher species richness of microbial communities. Our study pointed out the existence of negative relationships between fungal diversity and soil invasibility by non resident microbes. Therefore, the loss of microbial species may adversely affect ecosystem functionality under specific environmental conditions.     

An optimized microsatellite marker set for detection of Metarhizium anisopliae genotype diversity on field and regional scales

Thirty-three Metarhizium anisopliae isolates sampled across Switzerland as well as 35 and 36 M. anisopliae isolates sampled from two field sites were assembled in three isolate collections. All isolates were analyzed using 27 newly developed and 14 previously published microsatellite markers. The 41 markers allowed for detection of 25 genotypes in the Swiss collection while 30 and 11 genotypes were detected in the two field collections. This indicated high genetic diversity on a regional as well as on a field scale. In order to improve genotyping efficiency, an optimized marker set, which allows discrimination of a large number of genotypes with as few markers as possible was developed. The optimized marker set consisted of 16 common markers, which provided resolution close to maximal resolution in all three collections (91–93 %). The results demonstrated that optimized marker sets have to be validated before large scale application to previously unassessed collections in order to avoid suboptimal resolution. This genetic tool will be valuable for analyses of genetic population structure of M. anisopliae in different habitats on a regional as well as on a field scale.     

植物遗传多样性与生态系统功能关系的研究进展

全球变化和人类活动导致物种生境的萎缩, 造成很多植物种群数量缩减, 遗传多样性快速丧失。对于物种多样性低的生态系统, 优势种的遗传多样性可能比物种多样性对生态系统功能产生更大的影响。因此, 了解遗传多样性和生态系统功能的关系(GD-EF)及其机制对生物多样性保护、应对环境变化和生态修复具有指导意义。该文综述了植物遗传多样性对生态系统结构(高营养级生物群落结构)和生态系统功能(初级生产力、养分循环和稳定性)的影响及机制、功能多样性对GD-EF的影响、遗传多样性效应和物种多样性效应的比较, 以及GD-EF在生态修复等实际应用的研究进展。最后指出当前研究的不足之处, 以期为后续研究提供参考: 1)还需深入研究GD-EF机制; 2)未评估遗传多样性对生态系统多功能性的影响; 3)不同遗传多样性测度对生态系统功能的影响不明确; 4)缺少长期的和多空间尺度结合的GD-EF实验; 5)遗传多样性效应相对于其他因子的作用不清楚。     

Feeding by Hessian fly [Mayetiola destructor (Say)] larvae does not induce plant indirect defences

Abstract.  1. Recent research has addressed the function of herbivore-induced plant volatiles in attracting natural enemies of feeding herbivores. While many types of insect herbivory appear to elicit volatile responses, those triggered by gall insects have received little attention. Previous work indicates that at least one gall insect species induces changes in host-plant volatiles, but no other studies appear to have addressed whether gall insects trigger plant indirect defences.
2. The volatile responses of wheat to feeding by larvae of the Hessian fly Mayetiola destructor (Say) (Diptera: Cecidomyiidae) were studied to further explore indirect responses of plants to feeding by gall insects. This specialist gall midge species did not elicit a detectable volatile response from wheat plants, whereas a generalist caterpillar triggered volatile release. Moreover, Hessian fly feeding altered volatile responses to subsequent caterpillar herbivory.
3. These results suggest that Hessian fly larvae exert a degree of control over the defensive responses of their host plants and offer insight into plant-gall insect interactions. Also, the failure of Hessian fly larvae to elicit an indirect defensive response from their host plants may help explain why natural enemies, which often rely on induced volatile cues, fail to inflict significant mortality on M. destructor populations in the field.     

植物挥发性单萜经土壤载体的化感作用——以三裂叶豚草(Ambrosia trifida L.)为例

植物释放的挥发性单萜在生态系统中起着重要的作用,这些单萜不仅能以空气为载体对其他植物显示直接的化感作用,而且也能以土壤为载体进行间接的化感作用.通过对三裂叶豚草挥发物对植物种子萌发和土壤微生物种群影响及其化学成分的鉴定研究,验证了以单萜类物质为主的三裂叶豚草挥发物可以经土壤载体对其他植物及土壤微生物显示化感效应.还对植物挥发物化学成分鉴定的GC(气相色谱)和GC-MS(气相色谱-质谱联用)方法存在的一些误区进行了澄清,这将有助于对生态系统中植物挥发物化感作用的研究和认识.     

Diversity of plant evolutionary lineages promotes arthropod diversity

Large‐scale habitat destruction and climate change result in the non‐random loss of evolutionary lineages, reducing the amount of evolutionary history represented in ecological communities. Yet, we have limited understanding of the consequences of evolutionary history on the structure of food webs and the services provided by biological communities. Drawing on 11 years of data from a long‐term plant diversity experiment, we show that evolutionary history of plant communities – measured as phylogenetic diversity – strongly predicts diversity and abundance of herbivorous and predatory arthropods. Effects of plant species richness on arthropods become stronger when phylogenetic diversity is high. Plant phylogenetic diversity explains predator and parasitoid richness as strongly as it does herbivore richness. Our findings indicate that accounting for evolutionary relationships is critical to understanding the severity of species loss for food webs and ecosystems, and for developing conservation and restoration policies.     

The unseen majority: soil microbes as drivers of plant diversity and productivity in terrestrial ecosystems

Microbes are the unseen majority in soil and comprise a large portion of life's genetic diversity. Despite their abundance, the impact of soil microbes on ecosystem processes is still poorly understood. Here we explore the various roles that soil microbes play in terrestrial ecosystems with special emphasis on their contribution to plant productivity and diversity. Soil microbes are important regulators of plant productivity, especially in nutrient poor ecosystems where plant symbionts are responsible for the acquisition of limiting nutrients. Mycorrhizal fungi and nitrogen-fixing bacteria are responsible for c. 5–20% (grassland and savannah) to 80% (temperate and boreal forests) of all nitrogen, and up to 75% of phosphorus, that is acquired by plants annually. Free-living microbes also strongly regulate plant productivity, through the mineralization of, and competition for, nutrients that sustain plant productivity. Soil microbes, including microbial pathogens, are also important regulators of plant community dynamics and plant diversity, determining plant abundance and, in some cases, facilitating invasion by exotic plants. Conservative estimates suggest that c. 20 000 plant species are completely dependent on microbial symbionts for growth and survival pointing to the importance of soil microbes as regulators of plant species richness on Earth. Overall, this review shows that soil microbes must be considered as important drivers of plant diversity and productivity in terrestrial ecosystems.     

植物挥发性单萜经土壤载体的化感作用——以三裂叶豚草（Ambrosia trifida L.）为例

植物释放的挥发性单萜在生态系统中起着重要的作用,这些单萜不仅能以空气为载体对其他植物显示直接的化感作用,而且也能以土壤为载体进行间接的化感作用。通过对三裂叶豚草挥发物对植物种子萌发和土壤微生物种群影响及其化学成分的鉴定研究,验证了以单萜类物质为主的三裂叶豚草挥发物可以经土壤载体对其他植物及土壤微生物显示化感效应。还对植物挥发物化学成分鉴定的GC (气相色谱) 和GC-MS (气相色谱-质谱联用) 方法存在的一些误区进行了澄清,这将有助于对生态系统中植物挥发物化感作用的研究和认识。     

Intraspecific diversity and dominant genotypes resist plant invasions

Numerous studies have asked whether communities with many species deter invasions more so than do species-poor communities or whether dominant species deter invasion by colonizing species. However, little is known about whether high intraspecific diversity can deter biological invasions or whether particular genotypes might deter invasions. In this study, we present experimental evidence that intraspecific diversity and particular genotypes of tall goldenrod, Solidago altissima , can act as a barrier to colonization by new species. We found that biomass of colonizing species was negatively correlated with genotypic diversity, and particular genotypes affected the richness, cover, and biomass of colonizing species. Stem density of S. altissima increased with genotypic diversity and varied among genotypes, suggesting that stem density is a key mechanism in limiting colonization dynamics in this system. Our results indicate that the loss of intraspecific diversity within a dominant plant species can increase susceptibility to plant invasions.     

Parasitoids as drivers of symbiont diversity in an insect host

Immune systems have repeatedly diversified in response to parasite diversity. Many animals have outsourced part of their immune defence to defensive symbionts, which should be affected by similar evolutionary pressures as the host’s own immune system. Protective symbionts provide efficient and specific protection and respond to changing selection pressure by parasites. Here we use the aphid Aphis fabae, its protective symbiont Hamiltonella defensa, and its parasitoid Lysiphlebus fabarum to test whether parasite diversity can maintain diversity in protective symbionts. We exposed aphid populations with the same initial symbiont composition to parasitoid populations that differed in their diversity. As expected, single parasitoid genotypes mostly favoured a single symbiont that was most protective against that particular parasitoid, while multiple symbionts persisted in aphids exposed to more diverse parasitoid populations, which in turn affected aphid population density and rates of parasitism. Parasite diversity may be crucial to maintaining symbiont diversity in nature.     

Emergent effects of ground beetles size diversity on the strength of prey suppression

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Differential susceptibility of lepidopterous pupae to infection by the nematode Neoaplectana carpocapsae

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