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。     

Predicting the response of Cabomba caroliniana populations to biological control agent damage

Abstract  Cabomba caroliniana is a submerged aquatic plant from South America that is becoming a serious weed worldwide. It spreads by seed and by fragmentation and has an extremely wide climatic range, invading lakes and ponds from tropical (Darwin, Australia: latitude 12°) to cold temperate regions (Peterborough, Canada: latitude 45°). There are currently no effective methods of managing cabomba infestations and funding has been allocated to research biological methods. Surveys have examined cabomba in its native range and have identified several potential biological control agents. The most promising are a stem boring weevil ( Hydrotimetes natans ) and an aquatic moth ( Paracles spp.). Here we predict the change in cabomba populations after the introduction of the biological control agents. Our predictions are based on quantitative surveys of cabomba populations at three lakes in south-east Queensland, qualitative observations of cabomba in its native range, and conceptual knowledge of how the realised niche of cabomba might be affected by herbivore damage.     

利用传统生物防治控制外来杂草的入侵

随着国际贸易的日益频繁,外来有害植物入侵,严重威胁我国的自然环境和生物多样性。利用从原产地引入食性较专一的天敌来控制外来杂草是杂草生物防治的主要方式之一,有保护环境一劳永逸的效果。简要介绍了国际生物防治概况,统计表明全世界至少有133种目标杂草进行生物防治,主要分布在菊科、仙人掌科和含羞草科,63科369种无脊椎动物和真菌作为杂草生物防治的天敌,利用最多的天敌是鞘翅目象甲科和叶甲科昆虫,其中大多数项目是治理外来杂草的。杂草生物防治最活跃的国家依次为美国、澳大利亚、南非、加拿大和新西兰。重点论述了利用传统生物防治方法防治外来杂草的经典项目、国内外研究概况,以及目前面临的问题和应用前景。我国杂草生物防治起步晚,传统杂草生防的目标杂草有4种,紫茎泽兰、空心莲子草、豚草和水葫芦,其中,空心莲子草的生物防治获得成功。共引进天敌14种,输出天敌23种,与世界上生物防治先进的国家比尚有距离。中国应充分借鉴国际成功经验,对外来杂草开展生物防治。中国的生物多样性在世界上占有十分独特的地位,将在生物多样性保护中发挥重要作用。     

Comparison of two populations of Pseudophilothrips ichini (Thysanoptera: Phlaeothripidae) as candidates for biological control of the invasive weed Schinus terebinthifolia (Sapindales: Anacardiaceae)

Brazilian peppertree, Schinus terebinthifolia Raddi (Sapindales: Anacardiaceae) (hereafter Schinus), is one of the worst invasive species in Florida and Hawaii. The thrips Pseudophilothrips ichini Hood (Thysanoptera: Phlaeothripidae) is being considered as a potential biological control agent of Schinus. Two populations of this thrips were collected in the weed's native range; one from central-east Brazil (Ouro Preto thrips) and a second from north-east Brazil (Salvador thrips). Temperature requirements, adult fecundity and impact on different plant haplotypes by P. ichini were examined in the laboratory. Complete development of thrips from both populations occurred at temperatures ranging from 20 to 30°C. Two approaches were used to model the predicted distributions of the thrips populations in the USA: the physiological model (NAPPFAST) based on cold tolerance and the ecological niche model based on climatic variables (MaxEnt). The physiological model predicted that both populations of P. ichini may establish in similar areas of the USA, overlapping with the distribution of Schinus. However, the niche model predicted that only the Ouro Preto thrips could establish in the USA. The difference in model predictions suggests an apparent preadaptation of the Salvador thrips to lower temperatures than those experienced at the locations they were collected in Brazil. The Ouro Preto thrips had similar fecundity on two Florida Schinus haplotypes, whereas lower fecundity on haplotype A was found for the Salvador thrips. Based on these results, the Ouro Preto population may be better adapted to the climatic conditions and plant haplotypes found in Florida. Moreover, greenhouse studies indicated that Schinus growth was greatly reduced by thrips feeding, which may result in lower weed reproduction and densities in the field.     

The potential for biological control of invasive alien aquatic weeds in Europe: a review

A retrospective analysis shows that invasive, alien, free-floating and emergent aquatic weeds in Europe are good targets for classical biological control, and that genus-specific chrysomelid and curculionid beetles offer the most potential. Ludwigia spp., Azolla filiculoides, Lemna minuta, Crassula helmsii and Hydrocotyle ranunculoides should be prioritised as targets. Fungal pathogens have been under-utilised as classical agents but, whilst they may have some potential against free-floating weeds, they appear to be poor candidates against submerged species, although the suitability of arthropod agents against these difficult targets still merits investigation. The use of indigenous pathogens as inundative agents (mycoherbicides) shows some promise.     

Genetic diversity of alligator weed ecotypes is not the reason for their different responses to biological control

Biological control of alligator weed Alternanthera philoxeroides (Mart.) Griseb. using Agasicles hygrophila, a Chrysomelid beetle, has been successful in limiting growth in water, but not on land. In order to understand a possible genetic basis of this difference, technique using inter-simple sequence repeats (ISSR) markers was applied to analyse genetic diversity of this invasive weed. No genetic variation was detected not only within or between populations growing in the same habitats, but also between land- and water-grown populations. Thus we consider that the genetic variation is not the baseline factor resulting in the biological control difference in China. The differential success of pupation by the beetle may be related to the phenotypic plasticity of the plant stem diameter, rather than to genotypic factors.     

Opportunities for biological weed control in Europe

The development and application of biological weed control offer greatopportunities not only for farmers, nature conservationists and othervegetation managers but also for institutions and companies that wish tosell plant protection services and products, and for the general publicthat demands safe food and a visually attractive and diverseenvironment. Despite the obvious opportunities for biological weedcontrol, few control agents are actually being used in Europe. Potentialagent organisms have features that make them particularly strong anduseful for biological control, but they also have weaknesses. Weaknessesinclude a too narrow or too wide host specificity, lack of virulence, orsensitivity to unfavourable environmental conditions.Developing specific knowledge on the interaction between weeds andpotential biological control agents, as well as expertise to increasethe effect of control agents and so achieve sufficient weed control in acost-effective manner, should have the highest priority in researchprogrammes. From 1994 to 2000 most ongoing research on biological weedcontrol in Europe was combined in a cooperative programme. This COSTAction concentrated on the interactions between five target crop weedsand their antagonists (pathogens and insects), on furthercharacterisation of the specific blems and potential control agents andon the most suitable biological control approach.The next major challenge will be to apply the findings provided byCOST-816 to the development of practical control solutions. The leadingobjective of a new concerted research programme with European dimensionswill be to stabilise or even promote biodiversity in the most importantEuropean ecosystems by integrating biological weed control in themanagement of these systems.     

A proposal to use plant demographic data to assess potential weed biological control agents impacts on non-target plant populations

Weed biocontrol programs aim to reduce the spread and population growth rate of the target plant while stabilizing or increasing populations of those native species considered under threat by invasive plants. This goal is not unique to weed biocontrol but applies to all other invasive plant management techniques, though such information is rarely collected. Without this information, success of management interventions can be ambiguous, and regulatory agencies, the public, policy makers, funders and land managers cannot be held accountable for chosen treatments. A fundamental reform, including use of demographic studies and long-term assessments, are essential to guide weed biocontrol programs. We propose to add use of plant demography (an assessment of how environmental factors and ecological interactions, for example competition, disease or herbivory, may affect plant populations by altering survival, growth, development and reproductive rates of plant individuals) during host specificity risk assessments of potential biological control agents. Demographic models can refine assessments of potential impacts for those plant species that experience some feeding or larval development during host specificity testing. Our proposed approach to focus on impact on plant demography instead of attack on plant individuals is useful in appropriately gauging threats potential weed biocontrol agents may pose to non-target species after field release.     

外来入侵杂草传统生物防治的生态风险及其防范对策

长期大量实践说明,引进天敌防治外来入侵杂草的传统生物防治方法是治理外来入侵杂草的一条切实可行的有效途径,但对其潜在的生态风险——对本土生物的直接或间接不良影响不容忽视。利用传统评价方法预测候选天敌的生态风险存在缺陷,主要表现在：（1）寄主专一性测定过分依赖室内进行的生理寄主范围测定结果,对生态寄主范围（实际寄主范围）问题重视不够,后者指在新环境中的一系列物理和生物条件下的寄主利用预测;（2）在生理寄主范围测定中,过分依赖完成生长发育的可能性,对行为、遗传性状以及系统发育关系重视不够;（3）在风险评估中,过多强调对经济作物的风险,而对自然生态系统的风险重视不够。对此,建议：（1）鼓励对已释放的天敌进行回顾性跟踪研究,从而为杂草生物防治实践提供生态学理论支撑;（2）在运用生物防治手段对付外来入侵杂草实践中,建议采用“有害推论”的预防性原则,以避免在面临入侵生物重大威胁时草率做出释放天敌的决策;（3）在评估候选天敌风险中重视生态效应的风险评估。     

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.     

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.     

Strategies for the biological control of invasive willows (Salix spp.) in Australia

Abstract  Willows ( Salix spp.) are Weeds of National Significance in Australia where a large number of taxa are naturalised in temperate regions and can cause serious environmental degradation of riparian and wetland habitats. Several species are of economic or ornamental value and conflicts of interest could arise with planning their suppression. Biological control of six willow species ( S. alba L., S. cinerea L . , S. fragilis L., S. nigra Marshall, S. viminalis L., S . x  rubens Schrank) is under consideration in Australia using three approaches based on targeting different morphological structures. A rich phytophagous biota associated with Salix in their regions of origin indicate a range of organisms are available for development as biological control agents. Implementation strategies will depend on the host species targeted for biological control, their reproductive strategies, the level of control required to reduce environmental impacts and the level of conflict of interest associated with a biological control program.     

Biological control of alligator weed: Unsuccessful attempts to control terrestrial growth using the flea beetleDisonycha argentinensis [Col.: Chrysomelidae]

Biological control of alligator weed growing in aquatic habitats in Australia is successful but the agents, a flea beetleAgasicles hygrophila and a mothVogtia malloi, do not control terrestrial growth. Consequently another flea beetleDisonycha argentinensis was introduced into Australia specifically to control the terrestrial growth. Progeny of adults collected in Brazil from areas similar in climate and habitat to areas infested with alligator weed in Australia, were released but failed to become established. Eggs were laid by females released into a large field cage and some completed development, but the new adults failed to reproduce. Tentative conclusions are that microclimate or predation may have prevented establishment ofD. argentinensis but the results should not preclude attempts to establish this insect in North America, China or elsewhere.      

Optimizing nutritional conditions for the liquid culture production of effective fungal biological control agents

Spores of fungal pathogens of weeds and insects are unique in their ability to actively infect and kill their pest host. While these capabilities are advantageous in terms of their use as a contact biological control agent, or biopesticide, they also require special consideration during spore production. Directed approaches to medium optimization must consider not only spore yield but also spore qualities such as desiccation tolerance, stability as a dry preparation, and biocontrol efficacy. Nutritional conditions during culture growth and sporulation should direct the accumulation of appropriate endogenous reserves so that newly formed spores possess these advantageous qualities. Studies with the bioherbicidal fungus Colletotrichum truncatum and with the bioinsecticidal fungus Paecilomyces fumosoroseus have demonstrated the impact of nutrition on spore ‘fitness’ for use as a biological control agent. The optimization strategy used in these nutritional studies as well as a comparison of the results are presented. Received 06 February 1997/ Accepted in revised form 29 May 1997     

Impact of mowing and weed control on broadleaf weed population dynamics in turf

Abstract

Various turf management activities may influence weed population dynamics and interfere with weed control. The effects of a biocontrol agent, Sclerotinia minor, a chemical herbicide, Killex?, and mowing height on broadleaf weed dynamics were examined in two turfgrass stands for two consecutive years. Mowing did not reduce the population densities of dandelion or the ground cover of broadleaf weeds. In the second year, mowing significantly reduced white clover density, but significantly increased broadleaf plantain density, particularly at the closest mowing height (3–5 cm). Apart from the close height, the S. minor and Killex? treatments were equally effective in suppression of dandelion, white clover, broadleaf plantain, and prostrate knotweed in the second year. Common mallow increased in the herbicide treated plots and other species including yellow woodsorrel, yellow toadflax and lambsquarters increased in abundance in plots mowed at the 3–5 cm height and in plots treated with Killex?. Significant differences between the Killex? and S. minor treatments on dandelion population dynamics were rarely present and did not favour either treatment. S. minor did not damage the turfgrass, but Killex? reduced turf quality in 25% of the plots. The application of S. minor with a regular, medium height (～7 cm) mowing regime was highly effective in controlling broadleaf weeds in temperate Kentucky bluegrass turf.     

Plant-mediated interactions: Considerations for agent selection in weed biological control programs

Plant-mediated indirect interactions among herbivores (arthropods and pathogens) are common and extensively reported in the ecological literature. However, they are not well-documented with respect to weed biological control. Such interactions between biological control agents can have net positive or negative impacts on total weed suppression depending on the strength of the interaction(s), the relative importance of the agent indirectly impacted, and the combined weed suppression that results. A better understanding of plant-mediated interactions may improve decision-making about which agents to introduce in classical biological control programs for greatest impact on invasive weeds. This paper reviews the subject, including examples from the biological control literature; outlines the need for research on indirect effects of herbivores on other herbivores; discusses how such knowledge may strengthen classical biological control programs for invasive weeds; and provides recommendations for the kind of studies that should be done and how information about plant-mediated interactions could be integrated into agent evaluation protocols, to assist in decision-making about agents for importation and release.     

Biological control of waterhyacinth in Sinaloa Mexico with the weevils Neochetina eichhorniae and N. bruchi

Water hyacinth (Eichhornia crassipes (Mart.) Solms.)creates severe problems in the irrigationdistricts of Mexico, particularly in westernSinaloa. Therefore water hyacinth weevils(Neochetina eichhorniae Warner and N. bruchi Hustache), imported from the USA in1993, were used to initiate a biologicalcontrol program. Precautionary screeningrevealed that some were infected with amicrosporidian so disease-free colonies wereproduced by eliminating infected breedinglines. To demonstrate effectiveness prior toopen field releases, weevils were firstreleased in cages at field sites. Weevilintensity increased to 6.3 weevils/plant after320 days when the plants were all dead ordying. More than 8,600 N. bruchi and14,500 N. eichhorniae were then releasedat various sites during January 1995 to August1996. Waterhyacinth coverage declined atBatamote reservoir (134 ha) from 95% to <3%by 1997; at the 12-ha Hilda reservoir from100% in May 1995 to 1% by March 1998; at the42.3-ha Arroyo Prieto reservoir from 100% to1% during the same interval; and at theMariquita reservoir (492 ha), the largestreservoir in the Humaya system, from 394 ha(80%)to 98.4 ha (20%).     

Host range of the defoliator Strepsicrates sp. is too broad for biological control of the invasive weed Rhodomyrtus tomentosa

In its native range the invasive weed, Rhodomyrtus tomentosa is host to a suite of herbivores. One, Strepsicrates sp. (Lepidoptera: Tortricidae), was collected in China in 2014, introduced under quarantine in Florida, USA, and tested against related species to determine its host range and suitability for biological control. In no-choice tests, neonates fed and completed development to the pupal stage on several species of Myrtaceae, including the target weed R. tomentosa, the exotics Melaleuca quinquenervia, and Eucalyptus camaldulensis, and three native species, Eugenia axillaris, Mosiera longipes and Morella cerifera (Myricaceae). Due to the broad host range exhibited in quarantine testing, this species will not be pursued as a biological control agent of R. tomentosa.     

Success and safety in the biological control of environmental weeds in New Zealand

Biological control, using specialist insect herbivores and plant pathogens, can be a self‐sustaining, cost‐effective and low‐risk tool for the management of environmental weeds. Agents have been recorded attacking non‐target plants in New Zealand and elsewhere, but the effects are usually minor and/or transitory. It seems probable that only two cases, worldwide, will result in significant damage to non‐target plants (representing 0.5% of the nearly 400 insect, mite, or fungal species used in classical weed biocontrol). Both of these cases were predictable from host range testing. Negative indirect, or ‘downstream’, ecological effects from specific weed biocontrol agents are difficult to predict and measure. They are probably insignificant compared to the impacts of the invasive plants that the agents are introduced to control. However, it is necessary to balance the risks associated with any introduction against the environmental benefits from controlling a weed to a predicted level. Recent analyses suggest that success rates are better than generally perceived. For New Zealand programmes, where enough time has lapsed to allow assessment, we calculate a full/partial success rate of 83%. Many of the costs associated with environmental weeds are difficult to quantify. Detailed risk assessment will make biological control programmes more expensive and time‐consuming, so that reliance on non‐biological management methods for environmental weeds may actually increase. The costs of biocontrol programmes against some New Zealand weeds can be kept down by using research already carried out in Australia and other countries, and the process is reciprocal. Developing international consortia of sponsors is also a potential way to fund programmes against weeds shared by several countries.