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Biocontrol News and Information
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September 1999, Volume 20 No. 3
New Books
Enhancing Biological Control
This book*, edited by Charles Pickett and Robert Bugg, was a second brilliant major review on the subject of conservation biological control to appear in 1998 (the first was edited by Barbosa**). The theme is habitat management to enhance biological control, which the editors, in their introductory chapter define as "the provision of resources to natural enemies to improve their effectiveness at controlling pests". They also stress the important point that habitat management could be used in conjunction with classical biological control or augmentative biological control to enhance the establishment and/or impact of introduced or repeated releases of natural enemies. Like Barbosa's book, this book contains chapters on a wide range of important subjects authored by an international group of scientists: there are 15 contributions including ones from the United States, Finland, Germany, Great Britain, New Zealand, the People's Republic of China, and Switzerland.
Understandably, the `core' of the book, again like Barbosa's, is about effects of vegetational diversity, scale and mosaics on natural enemy diversity and activity and the identification of those resources (e.g. food sources and refuges) that are necessary to enhance the responses of natural enemies to their prey populations. Pickett & Bugg draw attention to the point that, despite the debates about diversity vs stability, most studies show that fewer crop pests are found as the diversity of an agro-ecosystem increases; and this has clearly been a stimulation behind much research underpinning habitat modification for biological control even though "to date, no comprehensive theory has been proposed to predict under what conditions and to what extent vegetational diversity may increase the effectiveness of natural enemies".
There are, however, important differences between this book and Barbosa's which, this reviewer believes, make them complementary. In Pickett & Bugg there is nothing on microbials, or the effects of pesticides or genetically modified (GM) crops on natural enemies. There is also less on ecological theory (but an adequate amount) but much on practical science and experimental design, which is very useful given the subject area. There is also a lot on important predatory groups such as spiders.
Chapters 1 and 6 (counting numerically from the introductory chapter - the chapters are not numbered) provide good reviews on the background and theory relevant to the subject and highlight some of the major issues: the inadequacies of simple host-predator models and the concept of stability for agro-ecosystems, the importance of polyphagous, highly mobile predators, and the dangers of applying simplistic thinking when trying to interpret the importance of vegetational diversity for natural enemy enhancement. Chapter 2 is theoretical and considers the effects and availability of vegetational strips in crops on the response of natural enemies with different dispersal capabilities. One of the model predictions is that when natural enemies are present in interplantings at crop germination, natural enemies are enhanced, even if strips provide more resources than the crop. Thus a key characteristic of vegetation management systems is whether natural enemies can overwinter in the interplantings. Some practical examples are provided for carabid beetles in wheat fields in chapter 15.
The resources necessary or likely for the enhancement of insect predators, parasitoids and spiders are covered in a number of the other chapters. Chapter 5 considers parasitoids and concludes that, contrary to theory, generalist and specialist parasitoids are equally enhanced by an increase in plant diversity. However, effects are variable and thus rather than seeking to increase crop diversity per se, agro-ecosystems should be designed to provide natural enemies with specific resources that will augment their efficiency. Chapters 6 and 4 discuss insect predators and chapters 8 and 13 spiders, and these conclude the same. There is an important discussion of the usefulness of artificial overwintering shelters for predators in chapter 9. The problems of providing resources for the natural enemies of one pest and creating another are illustrated in chapter 3; here various plants used to attract predators of lettuce aphids in California also resulted in population increases in the agromyzid leafminer Liriomyza huidobrensis. This illustrates the point that if pest diversity is high, relatively more may be gained by enhancing generalist predators than by enhancing or introducing a specific enemy against just one pest species. This in turn raises the question of considering agro-ecosystems as whole entities rather than trying to develop a suite of management packages for components such as individual pest species. There are two interesting chapters on this important subject. Chapter 14 discusses `farmscaping' in California while chapter 7 provides an overview of more ambitious integrated farming systems in Switzerland and how this can provide a model for other countries.
Agricultural practices are rapidly changing in many parts of the world. For example, in EEC countries, more farming land is becoming available for `set-aside' because of over-production of cereals. This important book provides guidance to researchers, agriculturalists and policy makers in why and how to design land-use systems that conserve natural enemies of agricultural pests.
*Pickett, C.H.; Bugg, R.L. (eds) (1998) Enhancing Biological Control. Berkeley, CA, USA; University of California Press, 422pp. Hbk. ISBN 0 520 21362 9.
[**Barbosa, P. (ed) (1998) Conservation Biological Control. San Diego, CA, USA; Academic Press, 396 pp. For a review of this title see BNI 19(4) 114N-115N.]
Cotton is one of the world's leading crops, and represents almost half the world's fibre market with cotton fibre production in 1997-98 estimated at 18,888,000 tonnes worldwide. It is grown on all the continents, in tropical, subtropical and warm temperate environments, from the monsoon tropics through Mediterranean climates to arid, near-desert conditions, by all sizes of producers from giant commercial concerns to smallholders. So it is almost inevitable that it should have acquired a vast array of pest and disease problems. For example, although most losses are caused by six species of bollworm, cotton is attacked by close to 50 different insect pests. Thus conventional cotton growing is heavily dependent on chemical inputs (nearly a quarter of insecticides used around the world each year is applied in cotton).
Concern about the environmental effects of cotton production and the welfare of cotton farmers and farmworkers has led to the promotion of a number of organic programmes in cotton, along with a growing niche market for pesticide-free and `ecological cotton'. Some programmes are highly sophisticated in terms of crop management and marketing, while many are organic more by default, where smallholders can no longer afford agrochemicals and cultivate their cotton in low-input mixed cropping systems.
Commercial organic cotton production is a new sector, barely ten years old, and in 1997 still had less than 0.05% of the world market. The independent development of alternative solutions to problems of cotton growing in a diversity of agro-ecological situations has led to a wide range of options being researched, developed and tested. This book* provides a good summary of the experiences of organic cotton production so far, which will help to remedy the dearth of publications in this field. Case study material is given prominence, and is drawn from both well-established and experimental projects to present an overview of developments to date with detailed examples from the USA, Peru, India, Turkey, Egypt and six subSaharan African countries.
The book draws together experience from a diversity of sources, including most of the current organic cotton projects worldwide, to provide the first comprehensive overview of organic cotton production. Chapters are arranged according to the stages in the cotton `chain', from farmer to consumer. The problems of the dominant cotton production systems, debate on the use of genetically-modified cotton varieties and the current state of organic production, processing and use are summarized, with a special emphasis on small-scale farming systems in developing countries. Technical aspects of organic cotton growing, including pest, weed and disease management are covered, as are marketing and project support requirements. Problems at the processing level, and approaches that are more environmentally responsible are discussed. Economic and marketing aspects and developments in regulatory systems are examined, including cost and yield comparisons of conventional and organic cotton, certification, price premiums, labelling and consumer demand. Perspectives on current problems and future developments are reviewed and the book contains a comprehensive list of 100 contacts and sources of support in producer and consumer countries.
Alternative cultural and biological practices to chemical control are outlined for major cotton pests such as boll weevil, bollworms, aphids, bugs and whitefly, within the context of a holistic approach with equal emphasis on soil health, water management and good crop husbandry. Augmentation of natural enemies is carried out by organic farmers in the USA, and some in India, Peru and, occasionally, Egypt and Turkey. In India organic farmers may release Trichogramma wasps and lacewings and use bacterial or viral products or collect viral-diseased larvae to prepare a crude biopesticide. In subSaharan Africa, biocontrol is currently limited to conservation of natural enemies. Many organic farmers in developing countries will also combat pests by sowing repellent plants such as marigold, trapcropping and intercropping, applying home-made botanical preparations and using yellow sticky and pheromone traps.
In Egypt there are now 150 biodynamic farms cultivating over 2000 ha. Biodynamic cotton seed is treated with Trichoderma harzanium and Bacillus subtilis for fungal disease control and sown with biodynamic preparations before covering with quartz sand. The warm sand helps to prevent cutworm (Agrotis ypsilon) attack. Whitefly, aphids, jassids and thrips are countered in early season by the use of yellow sticky traps at 30/ha. Dilute potassium soap solution or neem extract may also be applied. Irrigation timing is carefully regulated to prevent disease attack. Cotton leaf worm, Spodoptera littoralis, is controlled by collection and burning of egg masses and pheromone traps to disrupt mating. Bt sprays may be used if leafworm damage is evident. Delta traps are used for mating disruption of pink (Pectinophora gossypiella) and Helicoverpa bollworms. As a result of pesticide elimination, 64 species of predators, including vertebrates, are now observed in biodynamic fields, with Orius spp. the most common, followed by spiders, ladybirds and lacewings.
*Myers, D.; Stolton, S. (eds) (1999) Organic
cotton. From field to final product. London; Intermediate Technology Publications Ltd.,
267 pp. Pbk. ISBN 1 85339 464 5
Otainable from: Intermediate Technology Publications, 103/105 Southampton Row, London WC1B
4HH, UK.