杂草生防作用物对本土生物群落的影响

传统生物防治是治理外来入侵杂草危害切实可行的有效策略和途径,近来对传统生物防治的批评主要集注于,引进的生防作用物攻击威胁本土非靶标生物。引进的生防作用物可能对本土非靶标生物产生直接和间接影响,这类影响通过不同营养级生物之间的取食关系,以及通过同一营养级内生物间的竞争关系,而影响本土非靶标生物群落。列举若干杂草生物防治案例对以上影响方式及其发生途径进行了评述。就防范杂草生防作用物对非靶标生物的负面影响,提出了以下对策:(i)把引进天敌防治外来入侵生物作为最后的有效手段;(ii)适当增加对非靶标生物潜在影响的生态学评估;(iii)选择寄主专一性强而且能有效控制靶标杂草的天敌;(iv)加强对杂草传统生物防治的生态学研究。     

Ecological studies to assess the efficacy of biological control on populations of alligator weed and lippia

Abstract  The risk of non-target effects from biological control agents can be reduced if we can better identify effective agents prior to release. Introducing only those agents with high potential for effective control will reduce the number of agents released and reduce the probability of both direct and indirect non-target impacts. Identifying effective agents requires understanding the roles that resources, disturbances and herbivory play in regulating plant populations under natural field conditions. Here we propose a series of experiments that will contrast the mechanisms of population regulation of two invasive wetland plants, alligator weed ( Alternanthera philoxeroides ) and lippia ( Phyla canescens ), with native congener species, Alternanthera denticulata and Phyla nodiflora . We hypothesise that the native plants will have greater growth rates when nutrients are low and herbivores are present, whereas the introduced plants will exhibit greater growth rates when nutrients are high and herbivores are absent.     

Assessing the non-target impacts of classical biological control agents: is host-testing always necessary?

Release of a biocontrol agent in New Zealand is typically preceded by non-target testing of native or valued species. Nevertheless, if both the target pest and the natural enemy are very different from any native fauna, then there may be no scientific justification for host testing. Gonatocerus ashmeadi (Girault) (Hymenoptera: Mymaridae) is being considered as a biocontrol agent for glassy winged sharpshooter, Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), should the pest arrive. An assessment of the potential impact of G. ashmeadi on New Zealand’s Cicadellidae and Membracidae, from published literature data, indicates that none of these insects is at risk, as their eggs will not be recognised by the parasitoid because either their size or location places them outside the parasitoid’s search pattern. Consequently, there is no scientific case for any non-target host-testing to be carried out in containment.     

Avoiding conflicts between insect and weed biological control: selection of non-target species to assess host specificity of cabbage seedpod weevil parasitoids

Abstract:  Classical biological control of insect pests and weeds may lead to potential conflicts, where insect pests are closely related to weed biological control agents. Such a conflict may occur in the classical biological control of the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) in North America, which belongs to the same subfamily, Ceutorhynchinae, as a number of agents introduced or proposed for introduction against non-indigenous invasive weed species. We propose a step-by-step procedure to select non-target species and thereby to develop a non-target species test list for screening candidate entomophagous biological control agents of a herbivore pest insect in a way that would simultaneously evaluate non-target potential on weed biological control agents and other non-target species. Using these recommendations, we developed a non-target test list for host specificity evaluations in the area of origin (Europe) and the area of introduction (North America) for cabbage seedpod weevil parasitoids. Scientifically based predictions on expected host–parasitoid interactions and ecological information about the ecological host range in the area of origin can help avoid conflicts, while still allowing the introduction of safe and effective agents against both insect pests and weeds.     

A review of open-field host range testing to evaluate non-target use by herbivorous biological control candidates

One of the fundamental challenges of pre-release studies in classical biological weed control is to assess and predict the likelihood and consequences of non-target effects. Unless a candidate biological control agent is proven to be monophagous through conventional starvation and host-specificity tests in quarantine, open-field host range studies can be important in predicting the likelihood of non-target effects since they reveal the host selection of herbivores displaying the whole array of pre- and post-alightment behaviours. Over the course of its 53-year history, the purpose and the design of open-field host range studies have changed considerably, with more recent studies clarifying or refining specific questions related to one or a few test plant species and using a set design. We discuss the opportunities and challenges of this approach and suggest that future open-field host range studies should be more hypothesis-driven and apply different experimental designs that facilitate the interpretation of the results.     

The use of molecular assays to identify plant pathogenic organisms vectored by biological control agents

The planthopper Prokelisia marginata VanDuzee (Homoptera: Delphacidae) has beenconsidered for the biological control of theweed Spartina alterniflora Loisel(Poaceae) in Willapa Bay, Washington, U.S.A. Prokelisia marginata is a stenophagousphloem-feeding insect with the potential totransmit bacterial plant diseases that could bemoved by less-specific vectors to other plantspecies. Initial assays with PCR primers thatare putatively specific for phytoplasmas gavepositive results in Spartina. However,subsequent analyses did not indicate thetransmission of the pathogen by theplanthopper. We sequenced the 16S ribosomalRNA (rRNA) gene of the bacterial species thatgave positive results in PCR. Comparisons withsequences available in GenBank suggested thatthe positive results using the putativelyspecific PCR primers were due to the presenceof such bacteria as Pseudomonas, Holomonas, Vibrio, and Acinetobacter. We did not find phytoplasmasin either Spartina or the planthopperP. marginata.     

Testate amoebae community analysis as a tool to assess biological impacts of peatland use

As most ecosystems, peatlands have been heavily exploited for different human purposes. For example, in Finland the majority is under forestry, agriculture or peat mining use. Peatlands play an important role in carbon storage, water cycle, and are a unique habitat for rare organisms. Such properties highlight their environmental importance and the need for their restoration. To monitor the success of peatland restoration sensitive indicators are needed. Here we test whether testate amoebae can be used as a reliable bioindicator for assessing peatland condition. To qualify as reliable indicators, responses in testate amoebae community structure to ecological changes must be stronger than random spatial and temporal variation. In this study, we simultaneously assessed differences between the effects of seasonality, intermediate scale spatial variation and land uses on living testate amoebae assemblages in natural, forested and restored peatlands. We expected the effects of seasonality on testate amoebae communities to be less pronounced than those of land use and within site variation. On average, natural sites harboured the highest richness and density, while the lowest numbers were found at forestry sites. Despite small changes observed in taxa dominance and differences in TA community structure between seasons and years at some sites, spatial heterogeneity, temperature, pH, nor water table depth seemed to significantly affect testate amoebae communities. Instead, observed differences were related to type of land use, which explained 75% of the community variation. Our results showed that testate amoebae community monitoring is a useful tool to evaluate impacts of human land use on boreal peatlands.     

Ecological niche modelling of an invasive alien plant and its potential biological control agents

Invasive alien plants are of concern in South Africa. Pompom weed (Campuloclinium macrocephalum) is currently invading the Grassland and Savannah biomes of South Africa and is likely to continue spreading in the southern African sub- region. Two possible biological control agents (Liothrips tractabilis and Cochylis campuloclinium) have been identified for control of pompom weed. We used ecological niche modelling to predict which areas in southern Africa are likely to be suitable for pompom weed and the two potential biological control agents. The overlap between areas predicted to be highly suitable for pompom weed and areas suitable for the biological control agents was assessed. Methods of reducing sampling bias in a data set used for calibrating models were also compared. Finally, the performance of models calibrated using only native range data, only invaded range data and both were also compared. Models indicate that pompom weed is likely to spread across a greater region of southern Africa than it currently occupies, with the Savannah and Grassland biomes being at greatest risk of invasion. Poor overlap was found between the areas predicted to be highly suitable for pompom weed and those areas predicted to be suitable for the biological control agents. However, models of the potential distribution of the biological control agents are interpreted with caution due to the very small sample size of the data set used to calibrate the models. Models calibrated using both native range and invaded range data were found to perform best whilst models calibrated using only native range data performed the worst. There was little difference found between models that were calibrated using spatially reduced (selecting only one record per 30 min grid cell) and randomly reduced (randomly selecting 50% of available records) biased data sets.     

A faunistic approach to assess potential side-effects of genetically modified Bt-Corn on non-target arthropods under field conditions

A faunistic study investigating the potential side-effects of corn (Zea mays) genetically modified to express a truncated Cry1Ab protein derived from Bacillus thuringiensis subsp. kurstaki, on non-target arthropods was carried out under field conditions. The communities of non-target arthropods in the soil, on the leaves and flying in the crop area were monitored throughout the growing season. Water-treated, untransformed corn served as a control, and a spray application of a bacterial Bt insecticide (Delfin WG) and a synthetic insecticide (Karate Xpress) used to control the European corn borer (Ostrinia nubilalis; Lepidoptera: Pyralidae) acted as positive reference treatments. Results were analyzed using a principal response curve. Significantly lower infestations by the lepidopteran target species O. nubilalis were observed in the Bt-corn plots compared to the control. No effects of Bt-corn on the communities of soil dwelling and non-target plant dwelling arthropods were observed. A trend towards a community effect on flying arthropods was observed with lower abundance of adult Lepidoptera, flies in the families Lonchopteridae, Mycetophilidae and Syrphidae, and the hymenopteran parasitoids Ceraphronidae. Effects were weak and restricted to two sampling dates corresponding to anthesis. A short but statistically significant effect of Karate Xpress and Delfin was observed on the community of plant dwellers and a prolonged effect of Karate Xpress on the soil dwellers.     

The stability of host-pathogen interactions of plant disease in relation to biological weed control

A theoretical analysis was conducted to investigate the dynamics of plant-pathogen interactions for biological weed control. Computer simulation showed that the dynamics of plant-pathogen interactions can be determined by the properties of the pathogen. Pathogens with high levels of virulence may exist in nature in low frequencies due to high extinction rates. Pathogens of this type are suitable for the mycoherbicide strategy. Pathogens with a low level of virulence are frequent and may coexist stably with their host. Good candidates for the classical strategy may be the pathogens with intermediate pathogenicity, which maintain a stable interaction and a high control efficiency. The probability of extinction of a pathogen increases when pathogenicity is greater than a critical value at the intermediate range. The regulation of plant populations through reducing host reproductivity and increasing host mortality has similar results.     

Selection of pathogen agents in weed biological control: critical issues and peculiarities in relation to arthropod agents

Abstract  Plant pathogens are playing an increasing role in classical biological control of weeds worldwide. This paper presents an explicit framework consisting of various interconnected steps to facilitate and streamline the selection process for pathogen agents. It also highlights and discusses critical issues associated with the various steps of the selection framework such as the climatic-matching approach to find well-adapted agents, host–pathogen matching and pathogen genetic structure. Processes and issues relating to the selection of pathogens are then contrasted with those usually adopted for arthropod selection in weed biological control. In both cases optimising the level of genetic diversity in introduced agents is seen as beneficial to biological control success. The difference in regulatory approach for multiple and genetically pure pathogen strains vs. genetically variable arthropod agents is highlighted for further scientific debate.     

Global characterisation factors to assess land use impacts on biotic production

Purpose

The inclusion of land-use activities in life cycle assessment (LCA) has been subject to much debate in the LCA community. Despite the recent methodological developments in this area, the impacts of land occupation and transformation on its long-term ability to produce biomass (referred to here as biotic production potential [BPP]) — an important endpoint for the Area of Protection (AoP) Natural Resources — have been largely excluded from LCAs partly due to the lack of life cycle impact assessment methods.

Materials and methods

Several possible methods/indicators for BPP associated with biomass, carbon balance, soil erosion, salinisation, energy, soil biota and soil organic matter (SOM) were evaluated. The latter indicator was considered the most appropriate for LCA, and characterisation factors for eight land use types at the climate region level were developed.

Results and discussion

Most of the indicators assessed address land-use impacts satisfactorily for land uses that include biotic production of some kind (agriculture or silviculture). However, some fail to address potentially important land use impacts from other life cycle stages, such as those arising from transport. It is shown that the change in soil organic carbon (SOC) can be used as an indicator for impacts on BPP, because SOC relates to a range of soil properties responsible for soil resilience and fertility.

Conclusions

The characterisation factors developed suggest that the proposed approach to characterize land use impacts on BBP, despite its limitations, is both possible and robust. The availability of land-use-specific and biogeographically differentiated data on SOC makes BPP impact assessments operational. The characterisation factors provided allow for the assessment of land-use impacts on BPP, regardless of where they occur thus enabling more complete LCAs of products and services. Existing databases on every country’s terrestrial carbon stocks and land use enable the operability of this method. Furthermore, BPP impacts will be better assessed by this approach as increasingly spatially specific data are available for all geographical regions of the world at a large scale. The characterisation factors developed are applied to the case studies (Part D of this special issue), which show the practical issues related to their implementation.     

Scientific advances in the analysis of direct risks of weed biological control agents to nontarget plants

Research on host specificity testing protocols over the last 10 years has been considerable. Traditional experimental designs have been refined and interpretation of the results is benefiting from an improved understanding of agent behavior. The strengths, weaknesses, and best practice for the different test types are now quite clearly understood. Understanding the concept of fundamental host range (the genetically determined limits to preference and performance) and using this to maximize reliability in predicting field host specificity following release (behavioral expression of the fundamental host range under particular conditions) are still inconsistently understood or adopted despite having been identified as the critical steps in analyzing the threats posed by biological control agents to the agriculture and biodiversity of novel environments. This needs to be consistently understood and applied so the process of testing can follow a recognized process of risk analysis from hazard identification (identifying life stages of the agent that pose a threat and defining their fundamental host range) to uncertainty analysis based on the magnitude (predicted field host specificity following release) and likelihood of threats (predicted actual damage and impact) to nontargets. Modern molecular techniques are answering questions associated with subspecific variation in biological control agents with respect to host use and the chance of host shifts of agents following release. Guidelines for assessment of nontarget impacts need to recognize and adopt such recent developments and emphasize a general increased understanding of the evolution of host choice and the phylogenetic constraints to shifts in host use. This review covers all these recent advances for the first time in one document, highlighting how inconsistent interpretation by biological control practitioners can be avoided.     

Scientific advances in the analysis of direct risks of weed biological control agents to nontarget plants

Research on host specificity testing protocols over the last 10 years has been considerable. Traditional experimental designs have been refined and interpretation of the results is benefiting from an improved understanding of agent behavior. The strengths, weaknesses, and best practice for the different test types are now quite clearly understood. Understanding the concept of fundamental host range (the genetically determined limits to preference and performance) and using this to maximize reliability in predicting field host specificity following release (behavioral expression of the fundamental host range under particular conditions) are still inconsistently understood or adopted despite having been identified as the critical steps in analyzing the threats posed by biological control agents to the agriculture and biodiversity of novel environments. This needs to be consistently understood and applied so the process of testing can follow a recognized process of risk analysis from hazard identification (identifying life stages of the agent that pose a threat and defining their fundamental host range) to uncertainty analysis based on the magnitude (predicted field host specificity following release) and likelihood of threats (predicted actual damage and impact) to nontargets. Modern molecular techniques are answering questions associated with subspecific variation in biological control agents with respect to host use and the chance of host shifts of agents following release. Guidelines for assessment of nontarget impacts need to recognize and adopt such recent developments and emphasize a general increased understanding of the evolution of host choice and the phylogenetic constraints to shifts in host use. This review covers all these recent advances for the first time in one document, highlighting how inconsistent interpretation by biological control practitioners can be avoided.     

Isolation and characterization of soil Streptomyces species as potential biological control agents against fungal plant pathogens

The use of antagonist microorganisms against fungal plant pathogens is an attractive and ecologically alternative to the use of chemical pesticides. Streptomyces are beneficial soil bacteria and potential candidates for biocontrol agents. This study reports the isolation, characterization and antagonist activity of soil streptomycetes from the Los Petenes Biosphere Reserve, a Natural protected area in Campeche, Mexico. The results showed morphological, physiological and biochemical characterization of six actinomycetes and their inhibitory activity against Curvularia sp., Aspergillus niger, Helminthosporium sp. and Fusarium sp. One isolate, identified as Streptomyces sp. CACIS-1.16CA showed the potential to inhibit additional pathogens as Alternaria sp., Phytophthora capsici, Colletotrichum sp. and Rhizoctonia sp. with percentages ranging from 47 to 90 %. This study identified a streptomycete strain with a broad antagonist activity that could be used for biocontrol of plant pathogenic fungi.     

Is host‐specificity of weed biological control agents likely to evolve rapidly following establishment?

Over 352 herbivore species have now been intentionally introduced into new regions as weed biological control agents. Recent evidence shows that rapid and significant evolution in host-specificity can occur. The risk of non-target use by biological control agents increasing to unacceptable levels through rapid evolution therefore needs to be considered. In addition, weed biological control offers many as yet largely unexploited opportunities for improving our basic understanding of host-specificity and its evolution. We therefore evaluate the evidence that rapid evolution (1) alters the use of existing hosts, and (2) alters the fundamental host-range. Most cited examples of so-called host shifts from weed biological control were not the result of genetic change. There was only limited evidence of genetically altered performance on a non-target host and no evidence of altered fundamental host-range. We conclude, from both theory and the available data, that only altered use of existing hosts (through quantitative genetic changes) needs be considered when evaluating the risk of rapid evolution. Host-specificity testing methodologies can be improved and adapted to better assess the risk of occurrence of post-release evolution.     

A testing sequence for reducing rejection of potential biological control agents for weeds

Many insect agents, selected for the biological control of weeds and tested under restricted cage conditions, have been rejected as unsafe for introduction because of an apparent increase in host range compared with that observed under natural conditions. These aberrant results appear to be due to the insects' inability to follow the normal behavioural sequence based on appropriate cues which lead to correct host selection. It is suggested here that a reverse sequence of testing which progressively reduces the degree of restriction and deletes unattacked plants at each stage, until only a few remain to be tested under conditions as near natural as possible, would allow previously rejected insects to be used as biological control agents.     

Prioritisation of potential agents for the biological control of the invasive alien weed,Pereskia aculeata (Cactaceae), in South Africa

Pereskia aculeata Miller (Cactaceae) is an invasive alien species in South Africa that is native in Central and South America. In South Africa, P. aculeata outcompetes native plant species leading to a reduction in biodiversity at infested sites. Herbicidal and mechanical control of the plant is ineffective and unsustainable, so biological control is considered the only potential solution. Climatic matching and genotype matching indicated that the most appropriate regions in which to collect biological control agents were Santa Catarina and Rio de Janeiro provinces in Southern Brazil. Surveys throughout the native distribution resulted in 15 natural enemy species that were associated with the plant. Field host range data, as well as previous host plant records, were used to prioritise which of the species were most likely to be suitably host specific for release in South Africa. The mode of damage was used to determine which species were most likely to be damaging and effective if released. The most promising species prioritised for further study, including host specificity and impact studies, were the stem-wilter Catorhintha schaffneri Brailovsky & Garcia (Coreidae); the stem boring species Acanthodoxus machacalis Martins & Monné (Cerambycidae), Cryptorhynchus sp. (Curculionidae) and Maracayia chlorisalis (Walker) (Crambidae) and the fruit galler Asphondylia sp. (Cecidomyiidae). By prioritising the potential biological control agents that are most likely to be host-specific and damaging, the risk of conducting host specificity testing on unsuitable or ineffective biological control agents is reduced.