Evaluation of Pesticidal Properties of Euphorbia tirucalli L. (Euphorbiaceae) against Selected Pests Mwine Tedson Julius Promoter: Prof. Dr. ir. Patrick Van Damme Faculty of Bioscience Engineering, Department of Plant Production, Laboratory of Tropical and Subtropical Agriculture and Ethnobotany [email protected] Chairman of the jury: Prof. Dr. Bernard DeBaets, Faculty of Bioscience Engineering, Department of Applied Mathematics, Biometrics and Process Control, University of Gent, Coupure links 653, Gent, [email protected] Members of the jury: Prof. Dr. ir. De Clercq, Patrick, Faculty of Bioscience Engineering, Department of Plant Protection, University of Gent, Coupure links 653, Gent, [email protected] Prof. Dr. Kiseka, Joseph, D/Vice chancellor, Uganda Martyrs University, P. O. Box 5498, Kampala, [email protected] Prof., Dr. Papenbrock, Jutta, Institute of Botany, University of Hannover, Herrenhäuser Straße 2, 30419 Hannover, Germany, [email protected] Prof. Dr. ir Steurbaut, Walter, Faculty of Bioscience Engineering, Department of Plant Protection, University of Gent, Coupure links 653, Gent, [email protected] Prof. Dr. ir. Van Damme, Patrick, promoter, Faculty of Bioscience Engineering, Department of Plant Production, Laboratory of Tropical and Subtropical Agronomy and Ethnobotany, Coupure Links 653, B- 9000 Gent, [email protected] Dean: Prof. Dr. ir. Guido Van Huylenbroeck Rector: Prof. Dr. Paul Van Cauwenberge JULIUS TEDSON MWINE EVALUATION OF PESTICIDAL PROPERTIES OF EUPHORBIA TIRUCALLI L. (EUPHORBIACEAE) AGAINST SELECTED PESTS Thesis submitted in fulfillment of the requirements of the degree of Doctor (Ph.D.) in Applied Biological Sciences Dutch translation: EVALUATIE VAN PESTICIDE-EIGENSCHAPPEN VAN EUPHORBIA TIRUCALLI L. (EUPHORBIACEAE) OP GESELECTEERDE PLAGEN Front and back cover photographs by Julius Mwine Front cover photo: Euphorbia tirucalli young pencil-like branches Back cover photo: Cabbage (Brassica oleracea L.) plants treated (R) and untreated (L) with E. tirucalli latex Correct citation Mwine J. T. 2011. Evaluation of Pesticidal Properties of Euphorbia tirucalli L. (Euphorbiaceae) against Selected Pests. PhD thesis. Faculty of Bioscience Engineering, Ghent University, Belgium 145pp. ISBN-number: 978-90-5989-423-5 The author and promoter give the authorization to consult and to copy parts of this work for personal use only. Every other use is subject to copyright laws. Permission to reproduce any material contained in this work should be obtained from the author Chapter one --------------------------------------------------------------------------------------------------------- Introduction Chapter one Introduction 1.1 Background and justification of the study During the last few decades, environmental concerns have become an inevitable part of human livelihood. As a result, the search for safer and environmentally-friendlier implements for both agricultural and human use has become an important branch of science. More and more scientists are today involved in research trying to establish why there are now more catastrophes than ever before in terms of tsunamis, landslides, torrential rains, hurricanes, wild fires, severe pest attacks and more virulent and incurable diseases in plants and animals, wild and domestic, just as in humans. For example, Kundzewicz (2003) reports an increase of world floods frequency and severity in the last decade, while Van Aalst (2006) says that hurricanes have become harsher in the last two decades. Advanced technology i.e. computerized high precision implements and state of the art biotechnology, expected to solve these problems and ease man’s work, appears to be causing more problems than it is solving. Consequently, one generation after another, more and more unexpected happenings are inherited to the chagrin of not only man but the whole biosphere. The billion dollar question is: has man interfered with natural systems so much that there is a danger of complete breakdown of natural orders? Are calamities becoming the new order of events? 1.1.1 Climate change, environment and agriculture Probably, the most daunting problem for everyone today and among the most widely discussed issues as likely causes for prevailing environmental dilemmas, are global warming and climate change. The latter two are attributed to numerous causes including gaps created in the ozone layer by Ozone Depleting Substances (ODSs) such as organochlorides/chlorofluorocarbons (CFCs) and methylbromide, as well as an abnormal accumulation of Green House Gasses (GHGs), like carbon dioxide, methane and others that increase atmospheric thermal retention (Guo et al., 2001; Joos et al., 2001; Weatherly and Arblaster, 2001; Zillman, 2001). For example, Crowley (2000) observed that a 21st-century global warming projection far exceeds the natural variability of the past 1,000 years and is greater than the best global temperature change estimate for the last interglacial period. He continues to say that natural variability only plays a subsidiary role in this global warming and that the most parsimonious explanation for most of the warming is an anthropogenic increase in GHGs. Evidence in support of his views has been provided in form of numerous models that have been developed (Gabric et al., 2005; He et al., 2005; Lo Monaco et al., 2005; Schultz and Lebon, 2005) and through direct observations of abnormal environmental occurrences (Allan et al., 2010; Thomas et al., 2004; Walther et al., 2002; Wolf and Woolf, 2005). Some specific observations include: changes in coral reef composition and rate of formation (Baker et al., 2004); decline in number and breeding behaviour alterations of migratory birds (Both et al., 2006); changes in outbreak ranges of insects 2 Chapter one Introduction (Williams and Liebhold, 2002) as well as change in precipitation trends (Kasei et al., 2010; Zhu and Meng, 2010) among others. CFCs and methylbromide which are said to be the main ODSs (Butchart and Scaife, 2001; Fraser, 1997; Tokioka, 1990) are mainly anthropogenic (Dameris et al., 2007; Manning et al., 1996; Tanhua et al., 2006). Main sources have been identified as: industrial, agricultural and domestic (Cartwright, 1993; Fraser, 1997; Gros et al., 2003). Mitigation measures should therefore focus on the reduction of emissions of ODSs as recommended by the Montreal and Kyoto protocols (Velders et al., 2007; Wittneben et al., 2006). The climate change story may be vast and mind-boggling but the sober truth is that each of us has in a way contributed to the problem and should therefore play his role of whatever magnitude in order to mitigate its ugly impact. As agronomists, our cardinal function is to produce food. We should ensure that safe food is available in required quantity and quality not only for today but also for tomorrow. It is our obligation to ensure that production means used do not overexploit or adulterate (pollute) the environment for the benefit of the next generation. As a Kashmiri proverb puts it ‘we have not inherited the world from our forefathers, we are borrowing it from our children’. The implication is that resources ought to be used rationally for purposes of sustainability. Therefore, agronomists should be environmentalists. They should bear in mind how the environment may be affected by agricultural activities. Zinn and Blodgett (1989) lament, that there is a gap between agronomists and environmentalists. They state that numerous agronomists focus on maximizing production, regardless of environmental impact. This implies that they over/misuse resources in such a way that what matters to them is just the harvest. In the same perspective, Goldburg (1992) reports that some pesticide-producing companies promote environment-unfriendly chemicals and block research into alternative technologies that are environment-friendly to improve their sales. This is likely to be dangerous to the environment. It should be remembered that most resources used in agricultural production i.e. soil, water, air and vegetation are consumables. They can be exhausted whereas their productivity depends upon how they are used. There are numerous examples where soil exhaustion has caused low harvests (Gold et al., 1999) and desertification has occurred due to poor methods of farming such as deforestation prior to cultivation (Anjum et al., 2010; Mulitza et al., 2010). Similarly, cases of diversity reduction and organism poisoning as a result of pesticide over/misuse have also been reported (Brittain et al., 2010; Rico et al., 2010). All these scenarios reflect the precarious balance of natural resources and remind us of how agriculture in particular and life in general can be affected by environmental degradation. 3 Chapter one Introduction 1.1.2 Pesticides and the environment Casida and Quistad (1998) predict that because of their unequalled and invincible characteristics, synthetic pesticides are bound to be ubiquitous and here to stay. Indeed, the invention of DDT was hailed by everyone and was seen as a panacea to all pest problems, while its inventor, Paul Müller, won a Nobel Prize in 1948. But as Palumbi (2001) comments, before the Nobel ceremony, resistance had been reported in house flies whereas resistance in mosquitoes followed by 1960s. These cases were shortly followed by The Silent Spring (Carson, 1962) where she states “.. chemicals have the power to kill every insect, the good and the bad, to still the song of birds and the leaping of fish in the streams,