A scientific approach to agent selection

Abstract  The prioritisation of potential agents on the basis of likely efficacy is an important step in biological control because it can increase the probability of a successful biocontrol program, and reduce risks and costs. In this introductory paper we define success in biological control, review how agent selection has been approached historically, and outline the approach to agent selection that underpins the structure of this special issue on agent selection. Developing criteria by which to judge the success of a biocontrol agent (or program) provides the basis for agent selection decisions. Criteria will depend on the weed, on the ecological and management context in which that weed occurs, and on the negative impacts that biocontrol is seeking to redress. Predicting which potential agents are most likely to be successful poses enormous scientific challenges. 'Rules of thumb', 'scoring systems' and various conceptual and quantitative modelling approaches have been proposed to aid agent selection. However, most attempts have met with limited success due to the diversity and complexity of the systems in question. This special issue presents a series of papers that deconstruct the question of agent choice with the aim of progressively improving the success rate of biological control. Specifically they ask: (i) what potential agents are available and what should we know about them? (ii) what type, timing and degree of damage is required to achieve success? and (iii) which potential agent will reach the necessary density, at the right time, to exert the required damage in the target environment?     

Host range tests reveal Paectes longiformis is not a suitable biological control agent for the invasive plant Schinus terebinthifolia

The most critical step during a weed biological control program is determination of a candidate agent’s host range. Despite rigorous protocols and extensive testing, there are still concerns over potential non-target effects following field releases. With the objective to improve risk assessment in biological control, no-choice and choice testing followed by a multiple generation study were conducted on the leaf-defoliator, Paectes longiformis Pogue (Lepidoptera: Euteliidae). This moth is being investigated as a biological control agent of Schinus terebinthifolia Raddi (Sapindales: Anacardiaceae), which is one of the worst invasive plant species in Florida, USA. Results from no-choice testing showed higher larval survival on S. terebinthifolia (48 %) and its close relative Schinus molle L. (47 %), whereas lower survival was obtained on six non-target species (<25 %). When given a choice, P. longiformis females preferred to lay eggs on the target weed, but oviposition also occurred on four non-target species. An improved performance on the native Rhus aromatica Aiton was found when insects were reared exclusively on this non-target species for one or two generations. Results from host range testing suggest that this moth is oligophagous, but has a preference for the target weed. Non-target effects found during multiple generation studies indicate that P. longiformis should not be considered as a biological control agent of S. terebinthifolia.     

Spatiotemporal variation in the strength of density dependence: implications for biocontrol of <Emphasis Type="Italic">Centaurea solstitialis</Emphasis>

Invasive plants often occupy large ranges in the introduced region and consequently, local population dynamics vary in ways that affect the potential for biological control. We used matrix models to describe how density and population growth rate of Centaurea solstitialis varies in time and space. Matrix models were parameterized with data collected over 4 years from invasions at the coast, interior valleys and Sierra Nevada Mountains in California (USA). Asymptotic population growth rates (λ) varied dramatically across all populations and years (0.24–6.45), density varied by an order of magnitude and had a measurable effect on survival and λ in all populations. We used simulations to estimate the degree to which a biocontrol agent would need to reduce plant survival to control the weed. Because seedling survival was dependent on density, an agent that reduced seedling density had the effect of increasing the probability that the remaining plants survived to flowering. Interestingly, this meant that in the highest density populations the plant had the largest compensatory response to agent attack and experienced decline (λ ≤ 1.0) only after heavy losses (≥90%) to the agent. Conversely, in populations where density was so low that it had only a weak effect on survival, the agent was able to control the plant (λ ≤ 1.0) at much lower levels of attack (≤50%). In other words, the impact of a biocontrol agent is predicted to be lower where the plant reaches its highest densities because the surviving plants, now experiencing less intraspecific competition, are more likely to survive to flowering and produce more seeds. This may also be true for other invasive species in which strong density dependent processes are operating. For this reason, prospective agents ought to target density-independence vital rates.     

Experts know more than just facts: eliciting functional understanding to help prioritise weed biological control targets

Prioritising investments in classical weed biological control (biocontrol) is a common decision-making challenge: biocontrol programmes can yield substantial benefits but are typically long-term and costly, and the outcome uncertain. Experts are often relied upon to help, but their role is generally restricted to providing facts and judgements to populate an existing prioritisation model, which in turn receives little scrutiny. We developed and applied a new prioritisation framework to guide biocontrol investment decisions by livestock industries that required eliciting experts’ functional understanding (including their in-depth knowledge of the theoretical and practical drivers of weed biocontrol programmes). This consultative and transparent framework drew on expertise from most biocontrol practitioners in Australia through a structured workshop, and the literature. Each of the 75 weed taxa considered was placed in a matrix according to their impact (current or potential) and the prospects of biocontrol achieving pre-defined management goals. There was considerable knowledge uncertainty regarding potential impacts, which is of concern when making pre-emptive investments. Feasibility (likelihood of finding host-specific agents) and likelihood of success (management goals being met, assuming that host-specific agents are available) of biocontrol were both assessed as low for 51 % of taxa. Predicted barriers to successful biocontrol were diverse and idiosyncratic, suggesting that application of more quantitative prioritisation approaches would be challenging. A short-list of 13 weed taxa was identified for further consideration as biocontrol targets, based on the trade-off between potential impact and prospects for biocontrol. Research priorities emerged from the prioritisation process that would maximise investment outcomes for each taxon. Only two short-listed taxa are new targets, reflecting the maturity of the biocontrol discipline targeting weeds of livestock industries in Australia. Accessing the in-depth functional understanding of experts resulted in explicit characterisation of the barriers to successful biocontrol and if/how they might be overcome, improved characterisation of uncertainty, and provided directed guidance for investment. Such an approach would be readily applicable to analogous decision-making challenges in other sectors and countries.     

Establishment and impact of insect agents deployed for the biological control of invasive Asteraceae: prospects for the control of <Emphasis Type="Italic">Senecio madagascariensis</Emphasis>

Several invasive Asteraceae have been targeted for biological control worldwide, with variable success. Senecio madagascariensis Poiret, which invades agricultural lands in Australia and Hawaii, is a recent target. Since several potential insect agents were recorded in the plant’s native range in South Africa, we assessed biocontrol efforts against asteraceous weeds to determine those most likely to deliver success. Some 108 insect species, from five orders and 23 families, were deployed against 38 weed taxa, mostly in the mainland USA, Canada, Australia and New Zealand. Coleoptera (mainly Curculionidae and Chrysomelidae), Diptera (Tephritidae) and Lepidoptera (Tortricidae) featured the most. Despite high establishment success (73% of releases across countries), only 37% of successful releases achieved meaningful impact. Although root-feeding and stem-feeding insects appeared to be the best candidates, neither insect family nor feeding guild significantly influenced the probability of success. This synthesis of the global contribution of different guilds of specialist herbivores to the management of invasive Asteraceae is guiding the selection of candidate agents for the biocontrol of S. madagascariensis in Australia.     

Factors affecting the cost of weed biocontrol programs in New Zealand

Many national schemes for setting priorities for invasive weed management have emphasized the current or future impacts of the weed more than the cost or feasibility of control, perhaps because the latter may be difficult to estimate. As part of a project to improve prioritization of weed biocontrol targets in New Zealand, we investigated factors that were hypothesized to influence the cost of conducting weed biological control, using data from New Zealand programs. Taxonomic isolation of the target weed, relative to commercially important plants and native flora was not a significant influence on program cost, although we present evidence that disease, which to date has only affected agents released against taxonomically isolated weed targets, has masked the importance of taxonomic isolation in New Zealand. Opposition to biocontrol has caused delays, but has not had a major influence on the cost of biocontrol in New Zealand, probably because weed species with the greatest potential for opposition were identified during feasibility studies and avoided, or because conflicts were resolved by conducting cost-benefit analyses that were minor components of the total program costs. Only two factors explained virtually all the variance in program cost: program type (repeat programs were cheaper than novel/pioneering programs); and the number of agent species released. The predicted cost of future weed biocontrol programs can now be incorporated into decision-making tools ranking New Zealand weed biocontrol targets. Efficiencies in future programs are most likely to be gained by better agent selection so that fewer agents are released. For repeat programs this could be achieved by waiting until monitoring has been conducted overseas, so that the best agents or combination of agents can be selected for any particular weed. This reiterates the need for better post-release evaluation of weed biocontrol agent effectiveness worldwide.     

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。     

Ecological,practical, and political inputs into selection of weed targets: What makes a good biological control target?

The topic of ecological, practical, and political considerations in the selection of weed targets for biological control has been widely discussed during the past two decades, mostly from the perspective of insect herbivores. For conceptual and practical purposes, plant pathogens have been treated in these discussions as if they are a subset of inoculative biocontrol agents, with little said about the inherent differences between pathogens and insects as biocontrol agents or the selection of weed targets for control by the inundative, bioherbicide strategy. Herein, I attempt to address the question of what makes a good biological control target for plant pathogens used as inoculative as well as inundative agents, basing my analysis on examples from the past three decades. Despite the small number of examples available for this analysis, the following generalizations can be made: (1) Weeds with robust capacity for vegetative regeneration are more difficult to control with pathogens than those that lack this trait. (2) A plant’s growth habit is not a reliable guide for target selection; weeds that have been successfully controlled include annual and biennial herbs, perennial shrubs, perennial vines, and trees, while numerous failures have been reported irrespective of the target’s growth habit or reproductive mode. (3) It is more challenging to control species with genetic heterogeneity and capacity for introgression than genetically homogeneous and reproductively conserved species. (4) Matching the target host’s susceptibility with the candidate pathogen’s virulence is of utmost importance for biocontrol success since host–pathogen interactions at the species and subspecies levels are often governed by single-gene differences (e.g., varietal specificity). (5) Practical and political considerations are central to the selection of targets for control with pathogens. (6) Demand from influential stakeholders for control and/or for a nonchemical or economically sustainable control typically drives the initiative as well as the continuance of biocontrol projects to their completion. (7) In the case of inundative, bioherbicide agents, the continuity and ultimate implementation of a project will be dictated by the prospects of economic returns from developing and using a pathogen. (8) The stakeholders’ perceptions of the effectiveness of a biocontrol program can be unpredictable, leading to conflicting views of “success.” In the final analysis, a good weed target for control by a pathogen is one that has strong stakeholder backing and the list of available pathogens for the target suggests a possibility of acceptable control at a cost that is competitive with those of other control options. While this conclusion is also applicable to target selection for insect biocontrol agents, it is more relevant for pathogens because of limited funding and personnel available for development of pathogens and the added cost and technological complexity of implementing bioherbicides compared to classical biocontrols.     

Plant/pathogen interactions observed during host range testing of the rust fungus Uromyces pencanus,a classical biological control agent for Chilean needle grass (Nassella neesiana) in Australia and New Zealand

Nassella neesiana (Chilean needle grass) is a South American grass species that is a serious weed in Australia and New Zealand. The rust fungus Uromyces pencanus is a promising biocontrol agent that could be used to control the weed in both countries. Extensive host range testing has been conducted to explore the specificity of the rust. In this paper we discuss the different degrees of invasion by the rust of the tissues of target and non-target species; the plant defences elicited by such invasion at the cellular level; and their relevance to the biological control of Chilean needle grass.     

Biological control: Premises,ecological input and Mimosa pigra in the wetlands of Australia's Top End

The adverse impacts of weeds on natural ecosystems, together with the inadequate outcomes from treating weeds as a symptom, have escalated interest in finding efficacious control methods. With the aim of protecting wetlands from invasive weeds, this contribution uses the woody shrub Mimosa pigra L. (mimosa) as a case history to examine the methodology of classical biological control and the reasons for the widely accepted 75% failure rate. Overall objectives are for all biocontrol agents to have the opportunity to fully express their potential and to insure that limited resources are spent wisely on attainable weed control. The three main conclusions were that (1) the premises on which biocontrol is based has restricted advancement of this method; (2) monitoring is the logical first step to improving the selection of agents and release sites; and (3) it may be more cost-effective to introduce fewer agents that have undergone agent/plant and host/home range pre- and post-release ecological studies. Weed control may remain elusive unless advantage is taken of every beneficial result. Innovative assistance to agents and the integration of different control methods may preserve a role for weed biological control and has the potential to be of great importance for future weed management. It is proposed that the climate in the Top End of the Northern Territory and the lack of competition on the floodplains has contributed to mimosa's invasiveness. Climate may also underly the difficulties faced by agents. Agents appear unable to impart effective control in the dry season because of low numbers which relates to mimosa's poor growth; nor in the wet season, when the impact from high numbers of agents is outstripped by mimosa's growth.     

Making weed biological control predictable,safer and more effective: perspectives from New Zealand

A persistent problem in weed biocontrol is how to reliably predict whether a plant that supports development in laboratory host-specificity testing will be utilized in field conditions, and this is undoubtedly preventing releases of safe and effective agents. Moreover, the potential for unanticipated undesirable indirect effects of weed biocontrol on ecological networks has raised concerns by policy-makers and the general public. The key to minimizing risks of non-target impacts is prioritizing candidate agents that are both host-specific and effective, such that the number of agents required to bring the weed under control is minimized. As a consequence both the weed and its biocontrol agents become minor components of the local biota. Here we review recent attempts in New Zealand to improve the predictive ability of host-range testing, to avoid potentially safe and effective agents being rejected. Research in New Zealand aimed at predicting whether an agent is likely to experience enemy-release (i.e. reduced parasitism and predation) could assist agent prioritization, potentially making biocontrol both environmentally safer and more effective.     

Melding ecology,classical weed biocontrol,and plant microbial ecology can inform improved practices in controlling invasive plant species

Early research leading to the successful biological control of invasive species such as Opuntia spp., and Hypericum perforatum set examples and provided data useful for research programs that would follow. However, this early work failed to become established as a source of applicable principles for later workers in weed biocontrol. Recently, retrospective and parallel studies have been suggested as a means to reengage with earlier work to derive useful ideas and data to enhance future programs in weed biocontrol. Parallel studies by workers in plant community ecology on the nature of feedback elicited by plant species in their invaded and native range have shown the importance of soil microbial communities in effecting feedback. Retrospective reexamination of previous studies would likely provide clues to other insect–plant pathogen interactions in addition to those described by the author and others. The effects of invasive species in profoundly altering soil microbial communities point to the need for further studies on key microbial species contributing to or driving the impact of biocontrol. These collective data suggest that the desired goal of selecting for and utilizing stronger biocontrol agents to reduce nontarget effects and to increase the impact of biological control programs would be best served by prerelease studies that assess the propensity of a candidate agent for direct or indirect interaction with other agents. This could be assessed through the use of survival analysis. Overall, parallel empirical and retrospective studies should be a necessary part of how biological control is practiced.     

Ecological, practical, and political inputs into selection of weed targets: What makes a good biological control target?

The topic of ecological, practical, and political considerations in the selection of weed targets for biological control has been widely discussed during the past two decades, mostly from the perspective of insect herbivores. For conceptual and practical purposes, plant pathogens have been treated in these discussions as if they are a subset of inoculative biocontrol agents, with little said about the inherent differences between pathogens and insects as biocontrol agents or the selection of weed targets for control by the inundative, bioherbicide strategy. Herein, I attempt to address the question of what makes a good biological control target for plant pathogens used as inoculative as well as inundative agents, basing my analysis on examples from the past three decades. Despite the small number of examples available for this analysis, the following generalizations can be made: (1) Weeds with robust capacity for vegetative regeneration are more difficult to control with pathogens than those that lack this trait. (2) A plant’s growth habit is not a reliable guide for target selection; weeds that have been successfully controlled include annual and biennial herbs, perennial shrubs, perennial vines, and trees, while numerous failures have been reported irrespective of the target’s growth habit or reproductive mode. (3) It is more challenging to control species with genetic heterogeneity and capacity for introgression than genetically homogeneous and reproductively conserved species. (4) Matching the target host’s susceptibility with the candidate pathogen’s virulence is of utmost importance for biocontrol success since host–pathogen interactions at the species and subspecies levels are often governed by single-gene differences (e.g., varietal specificity). (5) Practical and political considerations are central to the selection of targets for control with pathogens. (6) Demand from influential stakeholders for control and/or for a nonchemical or economically sustainable control typically drives the initiative as well as the continuance of biocontrol projects to their completion. (7) In the case of inundative, bioherbicide agents, the continuity and ultimate implementation of a project will be dictated by the prospects of economic returns from developing and using a pathogen. (8) The stakeholders’ perceptions of the effectiveness of a biocontrol program can be unpredictable, leading to conflicting views of “success.” In the final analysis, a good weed target for control by a pathogen is one that has strong stakeholder backing and the list of available pathogens for the target suggests a possibility of acceptable control at a cost that is competitive with those of other control options. While this conclusion is also applicable to target selection for insect biocontrol agents, it is more relevant for pathogens because of limited funding and personnel available for development of pathogens and the added cost and technological complexity of implementing bioherbicides compared to classical biocontrols.     

Laboratory biology and impact of a stem-boring weevil Apocnemidophorus pipitzi (Coleoptera: Curculionidae) on Schinus terebinthifolia

Brazilian peppertree, Schinus terebinthifolia Raddi (Anacardiaceae), was introduced into Florida, USA, from South America as an ornamental plant in the late 19th and early 20th centuries. It eventually escaped cultivation and is a serious threat to the state’s biodiversity. In the 1980s, this invasive weed was targeted for classical biocontrol. Surveys for natural enemies of Brazilian peppertree conducted in the native range resulted in the discovery of several candidate biocontrol agents. A stem-boring weevil identified as Apocnemidophorus pipitzi (Faust) was collected in Paraguay and transported under permit to Florida, USA. A laboratory colony of A. pipitzi was established in April 2007 by caging adults on cut branches of Brazilian peppertree supplemented with leaf bouquets. Adults are defoliators that feed mainly on the upper surface of subterminal leaflets. Females deposit eggs singly inside the stems and larvae feed under the bark where they damage the vascular cambium. There are five instars, pupation occurs inside the stem and a new generation is produced in 3–4 months. Growth of potted plants with and without exposure to weevil herbivory was compared over an 11-month period. Feeding damage by adults and larvae significantly increased leaf abscission and reduced leaf and root biomass accumulation.     

The European Weed Research Society and the Management and Ecology of Freshwater Plants

Attendance at the 9th International Symposium on Aquatic Weeds, held in Dublin in 1994, by 270 delegates from 35 different countries demonstrated the continuing interest in the management and ecology of freshwater plants. The relative importance of the various topics covered in this meeting is compared with that of the previous symposia (1967–1990) for which published proceedings are available. A shift of interest away from aquatic weed control towards ecology, plant-environment interactions and distribution is noted and demonstrates a growing recognition of the need for aquatic plant management. The interest in physical control has remained constant (5–12% of papers) whilst the interest shown in biological control over the period 1971 to 1982 has not been sustained in recent symposia. The international nature of the symposia has increased over the years with papers published rising from eight countries in the 1967, 1971 and 1974 symposia to 23, 18 and 20 in the last three. Consistent numbers of contributions have been made by delegates from the Netherlands, the Czech Republic and the United Kingdom with a significant and sustained increase since 1967 from the United States of America.     

近20年外来生物入侵危害与风险评估文献计量分析

外来生物入侵导致全球生物多样性下降,极大地威胁着生态系统健康,已造成很大的生态损失与经济损失。近年来,随着生物入侵的加剧,全球对生物入侵的研究力度不断加大。外来入侵生物的生态危害与风险评估可以为人们提供对入侵可能性和入侵方式更直接的信息,从而为管理者制定管理策略提供依据。基于最近20年间(1995—2014年)科学文献数据库Web of Science的科学引文索引数据库扩展版(SCI-E)中数据,对外来入侵生物的生态危害与风险评估方面的研究进行了文献计量分析,旨在了解当前国际研究现状,以便推动中国的生物入侵相关研究。为了全面掌握全球外来生物入侵生态危害与风险评估方面的研究,采用Bibexcel与TDA文献计量工具,对Web of Science数据库中相关文献进行了分析,去重后共获取5492篇文献。结果表明:近20年(1995—2014年)入侵生物的生态危害与风险评估方面的研究刊文量呈现前缓后剧增的趋势,2008—2014年进入了快速发展阶段,文献数量急剧增加,2014年达到最高(511篇);美国发文量远超其它国家,占据主导地位,中国刊文量排名第5。美国、澳大利亚、法国、英国、德国的研究论文影响力较大。刊文量最多的研究机构为美国农业部(USDA),中国科学院发文量排名第10位。研究学科主要为昆虫学、农艺学、植物科学、生态学,研究热点集中在生物防治、风险评估、粮食作物和经济作物的病虫害防治、杂草防控,以及生物入侵与气候变化的关系等方面。有关外来入侵生物的生态危害与风险评估的研究多集中于北美、澳大利亚和欧洲,未来要加强亚洲地区,特别是中国外来生物入侵风险评估的研究;要加强气候变化对外来生物物种特性的影响研究,更多关注入侵生物的生态控制与生态恢复方面的研究,以便更好地为今后长期有效地防控入侵生物提供理论与技术指导。     

Melding ecology, classical weed biocontrol, and plant microbial ecology can inform improved practices in controlling invasive plant species

Early research leading to the successful biological control of invasive species such as Opuntia spp., and Hypericum perforatum set examples and provided data useful for research programs that would follow. However, this early work failed to become established as a source of applicable principles for later workers in weed biocontrol. Recently, retrospective and parallel studies have been suggested as a means to reengage with earlier work to derive useful ideas and data to enhance future programs in weed biocontrol. Parallel studies by workers in plant community ecology on the nature of feedback elicited by plant species in their invaded and native range have shown the importance of soil microbial communities in effecting feedback. Retrospective reexamination of previous studies would likely provide clues to other insect–plant pathogen interactions in addition to those described by the author and others. The effects of invasive species in profoundly altering soil microbial communities point to the need for further studies on key microbial species contributing to or driving the impact of biocontrol. These collective data suggest that the desired goal of selecting for and utilizing stronger biocontrol agents to reduce nontarget effects and to increase the impact of biological control programs would be best served by prerelease studies that assess the propensity of a candidate agent for direct or indirect interaction with other agents. This could be assessed through the use of survival analysis. Overall, parallel empirical and retrospective studies should be a necessary part of how biological control is practiced.     

Trends in biological control: public interest,international networking and research direction

We investigated trends in biological control to both capture its evolution and explore future opportunities. We examined recent changes in public interest, international networking and peer-reviewed research. A Google Trends analysis revealed that the popularity of biological control is decreasing in terms of search hits on the internet. This trend is potentially worrying for the biological control community, given that public interest tends to drive political decisions regarding regulatory processes and governmental funding of research. To examine patterns of international collaboration, we established the list of authors who published their work in the three main biological control journals from the early 1990s to 2016. International co-authorship has intensified and the biological control sector is increasingly characterized by multilateral collaboration. We surveyed papers published in BioControl and Biological Control over the last 25 years to identify research trends with respect to target pests, commodities, biological control agents and biological control approaches. Finally, we report that articles on biological control are published in the broad-based scientific journals Science and Nature on a regular basis. This reflects contributions that biological control research makes to scientific discussions in general. Our analyses revealed a thriving scientific discipline with several major research trends in arthropod, plant pathogen and weed biological control.     

Polymorphic microsatellite markers in polyploid Lepidium draba L. ssp. draba (Brassicaceae) and cross‐species amplification in closely related taxa

Heart‐podded hoary cress, Lepidium draba L. ssp. draba (Brassicaceae) is a noxious invasive weed in the USA. At present, efficient biological control of this Eurasian native weed in the USA is hampered by lack of knowledge of its population genetic structure and colonization process. Here, we describe the development of 11 polymorphic microsatellite markers that also reveal the polyploidy of this weed. Successful cross‐species amplification highlights the possibility of using these markers for genetic studies in other closely related species.     

Integration of Herbicides with Arthropod Biocontrol Agents for Weed Control

Classical biological control of weeds using arthropods is being attempted on a large scale in a number of countries, sometimes with spectacularly successful outcomes. However, in many cases biocontrol is not completely effective and use of herbicides on weeds continues to occur, either in the presence of biocontrol agents or as an alternative to them. The ways in which the two techniques may interact are discussed, including direct toxicity of herbicides to biocontrol agents, responses to death of host plants and responses to sublethal changes caused by herbicides with different modes of action. A literature review for selected weed taxa showed that the great majority of publications relate to either chemical or to biological control techniques separately, with integration of the two seldom addressed. Possible reasons for this situation are discussed and some suggestions for future priorities are made.