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Biocontrol News and Information
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June 2000, Volume 21 No. 2
New Books
An Antipodean Perspective on Host-Specificity Testing
This slim A4 booklet* presents nine papers and a synthesis from a one-day workshop organized by the Co-operative Research Centre for Tropical Pest Management entitled `Introduction of exotic biocontrol agents - recommendations on host specificity testing procedures in Australasia' which was held in Brisbane on 3 October 1998. The papers are by a range of Australian and New Zealand scientists involved in biological control of weeds and arthropods, and provide a useful perspective of the different approaches currently being used or developed to assess host specificity of insect biological control agents.
This is a timely publication, given the current concerns regarding possible non-target effects of introduced biological organisms. In this debate, I think it is useful to distinguish between the science-based assessment of the potential host range of a biological control agent as opposed to the decision-making process itself. This has become obvious in the recent discussion of some of the non-target effects reported in the popular as well as the scientific literature. For example, the host range studies on Rhinocyllus conicus clearly showed that a range of thistles would be likely to be attacked if this weevil were released in North America, and hence the fact that it has now been able to do so should not come as a surprise. When R. conicus was first introduced into North America in the 1950s, the decision-making process did not consider the fact that it might feed on other thistles as a matter of sufficient concern to prevent its introduction (watch out for André Gassmann's useful review to be published by CABI in the proceedings of the IOBC Conference in Montpellier, October 1999 [see BNI 21(1), 14N-16N (March 2000) for a conference report], and the post-hoc review in preparation by André Gassmann and Svata Louda). It can be argued that the science was correctly carried out, but the decision-making process was contemporary, and that society's values change over time.
The subject matter of the volume reviewed here and the workshop it reports refers to the scientific process of evaluating the potential host range of biological control agents and does not consider the decision-making process. The editors have conveniently summarized the contents of the papers in the preface as follows:
"The first seven chapters focus on the various methodologies commonly used in the host specificity testing of candidate agents for biological control of weeds. Richard Hill explains the political and scientific usefulness for the commonly utilized no-choice trial. He takes the concept further than just the no-choice starvation test, but also considers extended fecundity and developmental trials of herbivorous insects and mites under no-choice conditions. Both Michael Day and Bill Palmer add to the understanding of the breadth and application of no-choice trials. Michael Day considers how results over multiple generation on non-target hosts can be interpreted, while Bill Palmer reviews the biological control literature and finds no evidence that using cut foliage for no-choice trials rather than whole plants can drastically alter the outcomes, at least for foliage feeding insects. Tim Heard summarizes a technique for host range testing insects that utilize discreet resources and which have mechanisms, such as the use of an oviposition-deterring pheromone, that tend to prevent them from over-exploiting resources. Penelope Edwards defines what constitutes a choice test, considers the usefulness of such tests, and make recommendations about their role, particularly as pertains to ascertaining oviposition and/or feeding preferences between plant species. David Briese reviews the literature surrounding open field host range tests, their rationale, and interpretation. His recommendation for a two-phase methodology appears to overcome a number of the current concerns about field tests. Andy Sheppard provides a thorough review of the biological control literature and reveals that, to date, no significant sequence of assay type has been predominant. He has produced an insect biology-based decision flowchart to suggest how the selection of the initial host range assay type could be most appropriately made.
"The next two papers discuss methods used in host specificity testing of parasitoids for biological control of arthropod pests. Barbara Barratt and co-authors provide an overview of requirements for host specificity testing of parasitoids. The regulatory requirements as well as the complexities of assay design for parasitoids are considered, and some modern technological aids to host range assessment are introduced. Michael Keller discusses the importance of having an understanding of the processes involved in host selection and clearly illustrates the relevant concepts with mainly parasitoid examples.
"Finally, Toni Withers discusses prospects for developing an integrated approach to host specificity testing to improve the accuracy of predicting field host range. How the order of host specificity testing assay type can be altered so that applications for released biological agents fit within a `best practice risk assessment' framework is discussed."
One thing that comes out very clearly from these reviews is the diversity of detail in the approaches used by scientists to assess the host specificity of the arthropods they study. I found this a very useful summary and reminder of some of the assumptions, difficulties, and potential pitfalls relating to the different approaches. It is clear that to test biological control agents for insect pests to the same level of predictability as for weed biological control agents will be challenging, time consuming and expensive.
Who needs to read this volume? Scientists involved in the study of host specificity of biological control organisms are the obvious audience. Scientists concerned with the potential impact of biological control organisms on non-target organisms should read it, and scientists who are tasked with the evaluation of applications for permission to introduce biological control organisms should certainly be familiar with the contents. It is not a how-to guide, but would be a very useful information source in developing such a guide. It is a snapshot of how biological control scientists in Australia and New Zealand were thinking in late 1998.
The binding on my copy is not very robust, and since in some sections the margins of the pages come close to the spine, I am not sure that it will last very well.
*Withers, T.M.; Browne, L.B.; Stanley, J. (1999) Host
specificity testing in Australasia: towards improved assays for biological
control. Indooroopilly, Queensland; Department of Natural Resources, 98
pp. Pbk.
Price: Au$30.00 + p&p; discounts for multiple purchases; credit card
payments accepted.
Obtainable from: (quoting item M12975): Scientific Publishing, Natural
Sciences Precinct, A Block, 80 Meiers Road, Indooroopilly, Queensland
4068, Australia
Email: Tanya.M.Brown@dnr.qld.gov.au
Fax: +61 7 3896 9672
By: Matthew Cock, CABI Bioscience.
A Handy Quarantine Reference
World trade in biological material for agriculture or forestry purposes (e.g. seed, new cultivars) is now at an all-time high; as with other world trade, this is largely a consequence of the impact of the General Agreement on Trade and Tariffs (GATT). A whole spectrum of national and international agricultural organizations is now demanding information on containment facilities and detection procedures that significantly reduce the risks of pests (insects and mites) or pathogens ending up in the wrong place. There is additional interest from the environmental sector and the general public concerned about the accidental introduction of non-indigenous species that may have adverse effects on ecosystems. Quarantine facilities are also of relevance to biological control workers meeting new demands for the screening of exotic biological control agents.
This book* attempts to meet all of these demands and by any measure is a brilliant effort. Kahn and Mathur have assembled a good cross section of authors who, together, provide a truly international and holistic view on the subject. Chapters are grouped under four main headings: background regulatory and biological concepts with two nice reviews by Kahn; safeguards and facilities mostly for seeds with some interesting reviews of facilities and safeguards at the international agricultural research centres; facilities and safeguards with emphasis on vegetative propagating materials with a good cross-section of reviews from the USA, Western Europe, Kenya, Malaysia and China; and lastly, facilities and safeguards for the deliberate importation of plant pests and pathogens which contains chapters covering plant pathogens, nematodes and general principles of design.
The stated objectives of the book are to "provide information about how quarantine and research services perceive the risk associated with exotic plants and other organisms, and how this risk may be managed through containment facilities and safeguards." To achieve this, the authors collate much widely scattered published and grey literature into a single-source reference about principles, concepts and guidelines relating to the design and function of containment facilities for high and low risk activities. The authors do not attempt to set particular international scientific `standards' but instead, provide examples of how various international research centres, governments and others have dealt with issues related to the import and export of plants, plant products and other organisms.
The magnitude of the problems to be grasped is nicely illustrated in the chapters covering the quarantine facilities at CIAT (International Center for Tropical Agriculture) and IITA (International Institute of Tropical Agriculture). The exchange of plant germplasm is an activity of major importance in the genetic improvement of cultivated species. The Genetic Resources Unit (GRU) of CIAT has been involved with the movement of some 65,000 bean seed samples to 83 countries and at least 27,000 tropical forage germplasm samples to 71 countries (chapter 5). Clearly there are real phytosanitary risks associated with the international movement of germplasm of this scale; in the case of CIAT, safe movement is managed by their GRU.
A knowledge of the life cycles of organisms to be contained is one of the most important factors necessary for the proper design of containment facilities and for implementing safeguards. Kahn (chapter 3) provides a good background discussion on this and on other biological concepts including pathway analysis; the latter is an evaluation of a pest's biology to assess the various ways that it could arrive in a new area. Kahn reminds us that quarantine activities are designed to reduce the risks of entry via manmade, and not natural, pathways.
In the chapters covering specific quarantine facilities, authors have included floor plans, diagrams, etc., and suggested biological and environmental standards, equipment needs, phytosanitation procedures, staffing and the results of pest and pathogen tests.
This book will be of interest to all those involved with the regulation of movement of biological material and is likely to become a standard reference text.
*Kahn, R.P.; Mathur, S.B. (eds) (1999) Containment facilities and safeguards for exotic plant pathogens and pests. St Paul, MN, USA; American Phytopathological Society, 213 pp. Hbk. ISBN 0 89054 197 3. Price: US$69.00
Obtainable from: APS Press St Paul Office, 3340 Pilot
Knob Road, St Paul, MN 55121-2097, USA
Fax: +1 651 454 0766
Email: aps@scisoc.org
APS Press Europe Branch Office,
Broekstraat 47, B-3001, Heverlee, Belgium
Email: apspress@pophost.eunet.be
Fax: +32 16 202535
American Phytopathological Society Website: http://www.scisoc.org
Nontarget Effects of Biological Control
Until about twenty years ago little consideration was given to the impact of biological control agents (principally exotic species introduced for control of introduced pests) on non-target organisms, except for efforts to avoid damage to crop plants by agents applied for weed control. Methodology for host range screening of weed control agents was developed primarily for this purpose, but agents for control of arthropods and other invertebrate pests were not screened. In fact, it was often stated that the existence of alternative hosts was an advantage in maintaining natural enemy populations when the target pest was scarce or absent. Decisions relating to the introduction, release and distribution of biological control agents were then taken chiefly by agricultural departments and other institutions, working on behalf of farmers.
The situation changed dramatically with the rise of concern for the environment and the preservation of biodiversity. Biological control practitioners who had proclaimed the advantages of relatively target specific control over the use of broad-spectrum chemicals suddenly found themselves accused of causing extinctions and other irreversible environmental damage. At first those questioning the practice of biological control focused chiefly on introduced agents, quoting supposed examples of non-target effects on native species, many of them based on hearsay or speculation. Documented examples are required so as to move from accusation to rational debate founded on facts and from there towards policies that will avoid or minimize non-target effects. To this end a symposium was held at the 1997 Annual Meeting of the Entomological Society of America. This book* contains chapters based on the eight presentations made at the meeting and a further nine others, written especially for it, on aspects of the biological control of insects by insects or weeds by insects. The editors explain the background in their preface and their intention "to achieve a balanced treatment of the diverse viewpoints and approaches" in order to "stimulate thinking and activity in this neglected area of applied biology". Have they succeeded?
The majority of the contributors are from the United States - only three of the 17 chapters are by scientists from other countries and focus on work undertaken elsewhere. Consequently, the majority of chapters dwell on the consequences of past introductions into the USA and the need for more effective regulation of introductions into that country. However, the contributions from New Zealand (Barbara Barratt et al.) and Australia (Toni Withers et al.) outline the strict and apparently effective procedures already in force in their countries. Also, little mention is made of the 1996 FAO Code of Conduct for the Import and Release of Exotic Biological Control Agents which has provided the stimulus for debate and legislation in a number of developed and developing counties that so far lack mechanisms for regulating biological control introductions.
The book is a compilation rather than a coherent text, no effort appears to have been made to edit the individual contributions so as to avoid repetition and improve readability - for example, most chapters begin with similar statements defining biological control and non-target effects and cite the same references in support. The grouping of chapters into sections on Perspectives, Parasitoids and Predators, Weeds and, lastly, Pathogens is not the most satisfactory arrangement as chapters describing the past, current effort to avoid future problems, and techniques for detection or evaluation of non-target effects occur in each section. Most contributions are concerned with the long term impact of introduced agents but the chapter on Trichogramma (David Orr et al.) in the Parasitoid and Predators section and the three chapters in the Pathogen section deal with the, chiefly short term, consequences of augmenting entomopathogenic fungi and nematodes and the effects of Bt sprays on non-target forest Lepidoptera. There is no editorial comment, except in the Preface, and no conclusion or synthesis to complete the work.
In the Perspectives section L. E. Ehler provides an introductory chapter discussing issues raised by past classical biological control of insects and calls for "a sensible balance between economic reality and environmental ethics". Jeffrey Lockwood follows with a philosophical discourse on the need to monitor ecological processes rather than individual species when measuring non-target effects. Peter Stilling and Daniel Simbeloff try to measure the importance of non-target effects by considering the average number of recorded hosts of introduced biological control agents and their attack rates on non-target hosts in order to counter the view of many practitioners that non-target effects are both weak and infrequent. Finally, Russell Messing discusses the impact of concerns about non-target effects on the conduct of biological control and calls for clear streamlined national regulations to allay fears of exotic species and to ensure the future for cost effective and environmentally sound biological control of exotic pests. Elsewhere in the book P. B. McEvoy and E. M. Coombs attack the "lottery model" of biological control whereby practitioners are under pressure to introduce many agents quickly in the hope that they will sort themselves out and some will bring about control.
More generally valuable are the chapters including case histories summarizing experimental work or quantitative observations made to measure non-target effects. These provide the facts which can help refine methodology that will minimize the chance of unwanted side effects from future introductions. Barbara Barratt et al. show that pre-release investigations on host ranges of braconid weevil parasitoids introduced into New Zealand were generally predictive of post-release field results. Peter Follett et al. describe studies on the impact of introduced parasitoids on Hawaiian Pentatomoidea and Jian Duan and Russell Messing evaluate non-target impacts of introduced fruit fly parasitoids in Hawaii. John Obrycki et al. discuss non-target effects of the introduction of generalist aphidophagous Coccinellidae into the continental USA. Toni Withers et al. outline the procedures used in Australia for risk assessment of weed control agents, using an example of an agent recently approved for release. Svata Louda summarizes her ongoing work on the adverse impact of the introduced weevil, Rhinocyllus conicus, on native American thistles and in the next chapter the background to this work is discussed by James Nechols in an overview of musk thistle (Carduus nutans) control in North America.
Several of chapters deal, in part, with techniques for evaluating non-target effects but the contribution by Jane Memmott is devoted entirely to describing food webs and their potential as a tool for qualitative and quantitative analysis of interactions between plants, herbivores and natural enemies.
So, to answer the question, the book provides fuel for thought and some facts for discussion but is very much concerned with the USA and the problems resulting from a decentralized nation state and a multiplicity of agencies participating in biological control. Much of the book dwells on past actions and their consequences, some contributors are judgmental but neglect to allow for changing attitudes and the pressures placed on practitioners to find solutions to what were perceived to be major threats to agriculture. Other authors recognise the need to strike a balance between economic necessity and preserving the environment so that biological control can continue to be used as an effective means of providing long term suppression of exotic arthropod pests, plant pathogens and weeds with minimal disturbance of non-target species.
In conclusion, the book provides a useful compendium of views, case histories and techniques which will stimulate further debate rather than a balanced overview of the subject or a recipe for future action.
*Follett, P.A.; Duan, J.J. (eds) (1999)
Nontarget effects of biological control. Boston; Kluwer Academic
Publishers, 316 pp. ISBN 0 7923 7725 7.
Price: US$140.00; UK£96.75;
Dutch Guilders 325.
