New Australian Classic

Australia was the source of the first insect natural enemies successfully imported for biological control of an arthropod pest; namely the very successful control of the cottony cushion scale (Icerya purchasi) in California by the vedalia beetle (Rodolia cardinalis) and a cryptochetid fly (Cryptochetum iceryae) in 1888-89. Australia was also one of the first countries to import arthropod natural enemies for biological control following news of this success. Thus, Australia has had more than a century of experience in biological control and is one of the top ten countries importing natural enemies. Thus, this new review1 is most welcome because the previous comprehensive review of biological control results in Australia by Frank Wilson2 was published in 1960 and much progress has been made since then, and some earlier results have been re-evaluated. This new book reviews results obtained against some 98 arthropod pests or groups of pests while Wilson reported on only 53 such attempts. Wilson also included attempts to control weeds, now covered in summary form on a worldwide basis and regularly updated by Mic Julien³.

The term 'classical biological control' to describe the importation of exotic natural enemies to control introduced pests came into general use around the time of the centenary of the introduction of the vedalia beetle into California and is in fact a misnomer, as other forms of biological control involving the augmentation of existing natural enemy species have been in use since at least the 3rd century AD when it is reported that nests of ants were being sold in the market in Canton for control of citrus pests. The meaning of the term is often extended, as in this book, to include natural enemies imported against native pests also.

The book is a fitting memorial to the late Doug Waterhouse who was a lifelong proponent of biological control, first in Australia while working for CSIRO Entomology and after his retirement when he promoted biological control in the Pacific Region and Southeast Asia. During his retirement he wrote, or was co-author of eleven other books reviewing biological control in these regions, showing how further progress might be made and identifying new targets. His co-author, Don Sands, has been actively involved in biological control projects in Australia and the Pacific for more than 20 years.

The main body of the book comprises separate chapters on each of the 98 pests or groups of pests. Each of these comprises a brief précis and succinct accounts of the biology, pest status and biological control. Where appropriate, in addition, there may be comments on the taxonomy of the pest, comments on the outcome of the biological control including suggestions for further work, short accounts of the biology of important control agents and tables listing native natural enemies. The results are summarized in a table that precedes the pest chapters and in a brief overview at the end. There is also a list of localities mentioned in the text and an outline map showing the position of each of them. The book is completed with an extensive reference list, an index of arthropod names (including authorities and classification) and a general index where other groups of organisms are similarly treated.

The final overview shows that highly or moderately effective control has been achieved against 30 out of 44 (i.e. 67%) exotic major pests in all or part of their range. Similarly effective controls have been achieved against 19 out of 28 (i.e. 68%) exotic minor pests but only 5 out of 15 (i.e. 33%) native (or presumed native) pests. Interestingly, 19 (or 63%) of the exotic major pests, 17 (or 89%) of the minor pests and 4 (or 80%) of the native pests against which useful results have been achieved are Homoptera. This follows the trend in other regions and has been frequently noted. However, the overall success rates are high in comparison with other regions and may reflect the isolation of Australia and its unique fauna and flora which has shown little resistance to invasion by exotic pests and, by inference, less resistance to the establishment of exotic natural enemies. In this respect the programme for control of cattle dung and dung breeding flies by the introduction of dung beetles is relevant, since Australia lacked both native ungulate herbivores and dung beetles specialized to utilize their dung prior to the arrival of European colonists.

Another probable reason for the relatively high success rate is the degree of effort, both in terms of research and funding, put into biological control programmes by CSIRO and State entomologists fulfilling DeBach's often quoted dictum that the results of biological control programmes are proportional to the effort. Throughout the 20th century Australia was noted for the extent of its research and insistence on rigorous evaluation of potential control agents before authorizing their introduction which has been shown to enhance the rate of successful introductions.

Since progress in biological control depends on past results which provide valuable information for future programmes against the same or related pests in other regions, this book will be an essential reference for biological control practitioners. It will also be a fruitful source of information for ecologists interested in analysing the results of introductions of exotic species, pest invasions and means to ameliorate their impact on native fauna and flora.

Finally, the book is produced to a high standard, but at a reasonable price for individuals who wish to possess their own copies of this authoritative review of progress in Australia against many widespread invasive pests of importance to agriculture, animal husbandry and human well being.

¹Waterhouse, D.F.; Sands, D.P.A. (2001) Classical biological control of arthropods in Australia. Canberra, ACT; ACIAR Monograph Series No. 77, 560 pp. Hbk. Price A$60.00. ISBN 0642457093 [Also available on CD: Price A$54.00.
ISBN 0642457107]

²Julien, M.H.; Griffiths, M.W. (eds) (1998) Biological control of weeds: a world catalogue of agents and their target weeds (4th ed) Wallingford, UK; CABI Publishing, 240 pp.

³Wilson, F. (1960) A review of the biological control of insects and weeds in Australia and Australian New Guinea. Farnham Royal, UK; Commonwealth Institute of Biological Control, Technical Communication No. 1, 102 pp.

By: D. J. Greathead

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Latest in Canadian Biocontrol

This book* is an extensive review of the biological control programmes against insects, mites, weeds and pathogens conducted in Canada between 1980 and 2000. Although not explicitly mentioned, it is one of the latest of CABI's Technical Communications, a series that is focused on providing a comprehensive review of biological control based on a country/regional basis. The Canadian contribution to this series has been substantial as three of the original series were devoted to reviews of Canadian biological control (No. 2 covered the early 20th century up to 1959; No. 4 dealt with the period 1959-68, and No. 8 1969-80). From this point alone, Canadian biological workers are to be congratulated for keeping their projects and programmes written up and published; biological control is still a practice that relies on previous experience more than on hard science and the Canadian experience is invaluable in this regard.

As the Editors point out, this volume differs from the previous reviews in some important ways. The increasing global problem of invasive species threats is treated as a subject in its own right and there is good discussion on how Canada is trying to balance regulatory legislation for these pests vs legislation for the introduction of biological control agents. The importance of taxonomy to biological control is given prominence. There is also much more on pathogens both as targets and as agents (the latter including pathogenic and antagonistic actions) than in earlier volumes. The pathogenic groups covered include viruses, bacteria, fungi and nematodes. There is also less on the introduction of insect agents, particularly for the management of forest pests. This approach in the book reflects the thrust of Canadian research over the last 20 years or so. The traditional grouping of pest problems in the Canadian volumes has also been changed for the better; insect pests of agriculture and forestry have been grouped together because several insect pests are a problem in both systems.

Canada is still investing heavily in biological control, and this technique of pest management is particularly relevant now environmental concerns have surfaced. Nonetheless, the focus of the Canadian work in biological control is fundamentally changing with more emphasis on the utilization of its own natural enemy resources. Many biological workers have contributed to this volume and the account of their combined experience makes essential reading for anyone engaged in this field.

*Mason, P.G.; Huber, J.T. (eds) (2002) Biological control programmes in Canada, 1981-2000. Wallingford, UK; CABI Publishing, 583 pp. Hbk. Price £95.00/US$175.00. ISBN 0 85199 527 6

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Scelionid Parasitoids of Acrididae

Scelio spp. have the distinction of being the only common hymenopterous parasitoids of Acrididae, which are unusual in having principally dipterous parasitoids. Scelio spp. are also the only important parasitoids of the egg stage of these insects. They have been reported from eggs of acridids on all the inhabited continents and have been studied as potential biological control agents, or important mortality factors, of many pest species. This book*, in spite of its title, contains a critical review of the world literature on the biology, ecology, host relations, and biological control significance of the genus Scelio. Therefore, it will be of interest for all concerned with the ecology or control Acrididae as well as specialists interested in the Scelionidae.

The book begins with a useful chapter detailing and critically reviewing methods for collection and rearing Scelio spp. as well as museum techniques for taxonomic studies. The next two chapters on biology and ecology will be the most useful for non-Australian readers undertaking field studies and pest management. It is shown that although Scelio spp. seldom achieve high levels of parasitism, they may sometimes help suppress host populations. Notably, one species from Malaysia, S. pembertoni, has been introduced in Hawaii for the control of the rice grasshopper, Oxya japonica, and is the only example of successful 'classical' biological control of an acridid pest. The proposed introduction of Scelio spp. into the USA for control of prairie grasshoppers is discussed. It was refused on the grounds that Scelio spp. are not host specific and that non-target species could be at risk. However, the authors also discuss the host range of Scelio spp. and provide a comprehensive world list of host records. They conclude that, at least some species of Scelio may not be as polyphagous as is often believed, and that their further use as biological control agents should not be rejected without further careful field studies to determine more precisely the determinants of host range. It is also suggested that Scelio spp. may be ineffective control agents in many instances because they are unable to adapt to environments modified by agriculture. This also implies that they are sensitive to changes in land use and action may be required to conserve species diversity.

It is stressed that systematic research is essential for establishing a solid framework for ecological studies and biological control alike. The remaining chapters set out to do this. They begin with a detailed description of the external morphology and a phylogenetic study of the genus (with particular reference to Australian species). A key to known males and females precedes the detailed descriptions of the Australian species, including the redescription of 33 species and the description of a further 26 new species. These descriptions are accompanied by drawings and SEM photographs illustrating the sculpture of the cuticle and by distribution maps for each species. The book is completed with a comprehensive reference list and indices to genera and species of scelionids and their hosts.

In conclusion, this is an excellent monograph and could usefully be used as a model for other such studies of taxa containing species of economic importance.

*Dangerfield, P.C.; Austin, A.D.; Baker, G.L. (2001) Biology, ecology & systematics of Australian Scelio: wasp parasitoids of locust and grasshopper eggs. Collingwood, Victoria, Australia; CSIRO Publishing, 254 pp. Price: A$170.00. ISBN 0643067035

By: D.J. Greathead

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Weed Risk Assessment

This book* is a timely publication in a new and expanding discipline: new, because risk assessment has rarely been considered, at least on a scientific basis, for plant species; and expanding, because increasing trade and globalization are leading to increasing plant movement - intentionally, as well as accidentally - between previously-isolated geographic regions, countries and continents. In order to prevent the predicted 'McDonaldization' of the world's flora, urgent action is required to better regulate and monitor such plant exchanges, and, thereby, to identify and 'weed out' the potential invasive species.

The threat from invasive alien weeds to ecosystems is ranked second only to habitat destruction and hence the book is aimed at a wide audience, from applied and theoretical life scientists to quarantine officers and policy makers. As reflected by the background of the editors, there is a strong Southern Hemisphere bias to the contents, although this strengthens rather than weakens the book since most of the relevant work on evaluating and managing alien weeds has been undertaken in this region. The 19 chapters, arranged under three main headings (Overviews, National Perspectives, and Regional Perspectives) with a final synthesis by the editors, embrace recent theories on plant invasions, as well as introducing various models for weed risk assessment and detailing procedures for ranking invasive species on a range of scales to assess weeds of both regional and national significance.

Australia, in particular, has put considerable resources into developing a scoring system for weediness and several chapters report recent significant advances resulting from initiatives by the Australian Weeds Committee which has promoted a National Weeds Strategy. The resultant Weed Risk Assessment System is described in detail (P. C. Pheloung) and generates a numerical score, based on answers to 49 simple questions, which is positively correlated with weediness. The example illustrated is Chromolaena odorata - or Siam weed as it is misleadingly called since it is of neotropical origin - but, from this reviewer's experience at least, several of the answers are questionable. For example, there is no doubt that this weed does exhibit allelopathic traits and that it also acts as a host for agricultural pests and pathogens: e.g. Zonocerus grasshoppers in West Africa and anthracnose (Colletotrichum spp.) in Asia. Nevertheless, there is no doubt that this will prove to be an extremely valuable and user-friendly method of predicting environmental hazards posed by alien plant species. Such a system is now essential since there has been a recent and fundamental shift in the position adopted by the Australian Quarantine & Inspection Service in their approach to regulating plant imports, abandoning a prohibited list in favour of a permitted list. In effect, this means that all plant species not on this permitted list are denied entry until they have been assessed for weediness. Importers previously supplied only details of the genus and species of plant to be introduced and, clearly, there was insufficient information on which to base an informed decision as to their potential weediness and the long-term threat to the environment. This reviewer is in no doubt that similar weed risk assessment systems should be universally adopted not only to keep out invasive alien plants but also the pests and pathogens they may be harbouring.

The book, therefore, is an essential read for all those involved, either directly or indirectly, in plant trade, especially quarantine policy makers; since, as the promotional blurb somewhat self-importantly proclaims, this "may help reduce weed impact and thereby improve living conditions for people throughout the world." It is something of a pity, therefore, that in the final synthesis, there is no attempt to at least summarize actual or potential management strategies for plant species which have already become invasive, especially, of course, the classical biological control approach which has been employed so successfully in the Southern Hemisphere against a number of alien weeds.

*Groves, R.H.; Panetta, F.D.; Virtue, J.G. (eds) (2001) Weed risk assessment. Collingwood, Victoria, Australia; CSIRO Publishing, 244 pp. Price A$80.00. ISBN 0 643 06561 X

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Tropical Weed Management

Weeds have plagued crop growing since the time the first plants were domesticated. Globally, about 8000 species of plants have been termed weeds; of these, around 250 are classed in the literature as serious weeds. The importance of weeds in world agriculture is well illustrated by the amount herbicides now used: during the last two decades, global pesticide sales have increased by about 250% and nearly half of these sales are for herbicides. This excellent book* is about weed management in the humid and sub-humid tropics. These two zones are characterized naturally by forest and savannah biomes respectively, and of course both are also characterized by a wide range of farming and cropping systems. Smallholder farms are particularly common in these regions. The soil fertility in both biomes is mainly an outcome of the balance between rapid plant growth and the breakdown of litter. In evergreen and monsoon forest areas, water erosion is important, and thus most investment is made in tree crops such as coffee, cacao and rubber. At the other end of the spectrum, in dry savannah areas where soil fertility is low, farmers mostly invest in annual crops.

Weeds are mostly a problem because they reduce yields of crops through competition; but weeds can have other important negative impacts such as being alternative hosts of pests and plant pathogens. As van Rijn points out, alarmingly, 17 of the world's worst weeds have a wide range of climatic and soil tolerance and are thus important in both the humid and sub-humid zones. Important species include Cyperus rotundus and Rottboellia cochinchinensis. However, besides these global weeds, there are many other troublesome weeds that are important on a regional basis. Good examples are the neotropical species, such as Chromolaena oderatum, which is highly invasive in the forests of tropical Asia, and other species such as Digitaria horizontalis and Euphobia heteropsylla, which are problematic in upland farming areas.

Van Rijn's book is an excellent review of the subject area. There is broad coverage and it is well referenced. The sequence of subjects is also satisfying. The first chapters cover weed impacts, ecology, and weeds in relation to different farming and cropping systems/crop performance in tropical regions. The section on weed ecology is refreshing as it underpins most of the book. All too often texts on weed science tend to focus on the problems related to particular management strategies whereas successful control can depend on a good understanding of the dynamics of the weed in question. Plants can have complex ecologies and van Rijn includes the important human dimensions that contribute to the dynamics of species such as human-mediated dispersal.

The next chapters in the book provide a brief review of the main weeds of the humid and sub-humid zones and then a review of main control methods. Ecological, cultural and mechanical control are obviously important in the zones covered by the book and these forms of management are given due prominence. Reviews of the current state of weed management in the major cropping systems are covered in the remaining chapters. There are sections on cereals, tuber crops, fruit crops, grain legumes/vegetable crops, plantation crops and weed fibres; there are also two additional sections by other authors covering pastures (L. 't Mannetje) and aquatic weed management (A. H. Pieterse). These sections leave a strong impression of the huge constraints that weeds pose to farmers. While those involved in cash crops may be able to afford herbicides, many smallholders still rely heavily on traditional methods of management. There is still much to be done to transfer the benefits of integrated management to smallholders. There is also scope for the development of biological control to complement traditional practices.

This is a book for researchers and extensionists. Most importantly, it will be an important resource for workers in the developing world where access to up-to-date information is sometimes hard to get. This book is a broad 'toolkit' of knowledge which introduces the interested worker to the current state of play and also provides the necessary links to other works with more detailed information.

*van Rijn, P.J. (2000)Weed management in the humid and sub-humid tropics. Amsterdam, The Netherlands; Royal Tropical Institute, 234 pp. Pbk.
Price i31.50. ISBN 90 6832 123 4

Contact: KIT Press, PO Box 95001,
1090 HA Amsterdam, The Netherlands
Email: publishers@kit.nl
Fax: +31 20 568 8286
Website: www.kit.nl

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