Integrated Pest Management in African Agriculture

Table of Contents

  I Integrated Pest Management in African Agriculture  

1  Introduction  3

1.1  Theory and Tactics of Pest Management  3

2  Conventional insecticides  5

2.1  DDT and chlorinated hydrocarbons  6

2.2  Botanical insecticides  7

2.3  Pyrethrum vs Pyrethroid  8

3  Biological control  10

3.1  Natural enemies  10

3.2  Biocontrol of cassava pests  13

4  Insect growth regulators  18

4.1  Juvenile hormone agonists  20

4.2  The practice of IGRs  22

5  Biotechnology  23

5.1  Bacillus thuringiensis  24

5.2  Management of maize pests in agribusiness  25

6  Conclusions and prospectus  28

  II Bibliography  31

  2  

1 Introduction

The history of mankind is a history of ambitions to get control over the environment. With the beginnings of agriculture, people suffered from crop losses due to insect pests that they henceforth tried to control.

Today global losses caused by pests are estimated to be US$ 300 billion annually,

an amount equal to 30-40% of potential food, fiber and feed production. 1 Facing the predictions of ongoing human population growth, there is a need to increase food production. Since World War II the use of chemical pesticides for agricultural intensification has led to dramatic yield increases in crops. But the control of insect pests on a long-term has not been achieved, rather severe problems concerning pest resurgence, undesirable environmental effects and human health problems have been the consequences - especially in developing countries. With the evident need of adapted pest control, the concept of integrated pest management yields hope to become a sustainable method of pest control for the future.

1.1 Theory and Tactics of Pest Management

There are various approaches to control pests in agriculture. According PEDIGO 1996, there are four main strategies to deal with insect pests:

1. Doing-Nothing

2. Reduce number of pest insects

3. Reduce susceptibility of the host

4. Combinations of 2 and 3.

At first sight, the Doing-Nothing Strategy seems to be preposterous, as a pest is harming the plant. But often, the host plant tolerates the insect pest with no consequences on economic losses in crop production. Therefore, the Doing-Nothing Strategy is always appropriate when pest densities are below the economic threshold. When densities reach the economic threshold as well as in a preventive manner, the Reduce-Number Strategy is applied. It is the most widely used strategy in pest management and various tactics are utilized. Most of the tactics aim to increase mortality of the pest by creating of intensifying hazards to insects. This may be via natural enemies, insecticides, many resistant cultivars, ecological modifications or insect growth regulators. The Reduce-Number Strategy can work on

1 cp.: Natural Resource Institute in: Thomas 1999, p. 5944

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reducing the carrying capacity so that the general equilibrium position 2 is lowered and highest population peaks will not reach the economic threshold. When the general equilibrium position is low compared to the economic threshold, dampening population peaks is the tactic. The strategy to reduce crop susceptibility does not modify the insect population at all. It minimizes crop losses by involving elements of host plant resistance or manipulations of the crop environment (e.g. fertilizer). Reducing the susceptibility to insect injury is considered to be one of the most effective strategy, while the last strategy, the combination of Reduce-Number and Reduce-crop-susceptibility has less vulnerability to failure. The diversification of strategies prevents economic losses when one tactic fails. 3 The integration of several compatible tactics to a sustainable pest management program is the goal of Integrated Pest Management (IPM). The application of a single tactic often fails in the long term because of insect’s ability to adapt to it. When several tactics are used in a combined program, the possibility to recover is lowered and sustainability of the pest management system can be achieved. Due to the application of different tactics, the use of pesticides decreases, so that integrated pest management systems are also less harmful to the environment. Definitions of Integrated Pest Management are various, ranging from a single separation from the conventional use of chemicals:

“use of various methods to combat pests as opposed to utilizing a single approach (chemicals)” [www.biotech.ca] to a complex proposal:

“A systems approach that combines a wide array of crop production practices with careful monitoring of pests and their natural enemies. IPM practices include use of resistant varieties, timing of planting, cultivation, biological controls, and judicious use of pesticides to control pests. These IPM practices are used in greenhouses and on field crops. IPM systems anticipate and prevent pests from reaching [www.soils.ncsu.edu].

This paper aims to give a general overview of selected practices of IPM methods, accentuated on African agriculture.

As the insecticide era began with the discovery of DDT in 1939, chapter 2 outlines the importance and impact of conventional insecticides. To demonstrate that the term 2 the pest’s long term average density

3 cp.: Pedigo 1996, p. 286ff

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insecticide does not always imply the devastating characteristics of DDT, .also botanical insecticides as part of IPM systems will be presented.

Moving from the insecticide era to the emerge of pest management in the 1950s, Chapter 3 deals with biological control as the axiom of integrated control. The African staple crop cassava, one of its major pests and the control by natural enemies will be portrayed as a typical case study of biological control.

The integration of control techniques expanded in later years to include other techniques. Referring to this, chapter 4 deals with the capabilities of insect growth regulators with emphasises on juvenile hormone agonists.

Chapter 5 moves to today’s daily headlines: the use of insect-resistant genetically modified plants for cultivation and human food consumption.

A final conclusion summarizes the different tactics of Integrated Pest Management

and leads to a critical perspective on the approach of truly integrated pest management.

2 Conventional insecticides

Derived from the Latin suffix „cida“ [killer], the word insecticide literally means killer of insects. The word pesticide is used in a more general context, meaning killer of any pest. Besides insecticides, pesticides include acaricides (mite and tick killers), herbicides, fungicides and nematicides. Conventional insecticides are mostly chemicals used for the control, prevention, destruction, repellence or mitigation of pests. Most conventional insecticides are nerve poisons killing insects very quickly while nonconventional insecticides, such as microbial insecticides and insect growth regulators, show slower actions and are not operating on the insect’s nervous system.

Pesticides are some of the most important chemicals for the wellbeing of humans. As they are maintaining human beings nutrition they have a great impact on our existence. Pesticides in agriculture are sustining and irreplaceable for the current quality and quantity of food and fibre production. After the development of modern synthetics in the 1940s, pesticide use increased constantly till the early 1980s when it reached an all-time high. For now, insecticides account for over one third of pesticides used in agriculture of the USA, about 750 insecticidally active ingredients are registered in the US Environmental Protection Agency (EPA). 4

4 cp.: Oregon State University 2007, http://oregonstate.edu/~muirp/pesthist.htm

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The great advantage of insecticides is their short-time effectiveness. Within hours, the active compounds of insecticides are working in the insect’s body and a pest population can be depleted within few days. In an economic sense, insecticides offer an easy way to prevent yield losses. They are easy to apply, even for unskilled persons and cost/crop ratio is around four to five dollars return for every dollar invested. 5 Nonetheless, insecticides have great impacts if they are used frequently. Main disadvantages on the agro-system are insecticide resistance, pest resurgence and pest replacement. Furthermore, insecticides are also harming non-target species like honey bees, fish and wildlife in and around the agroecosystem. Additionally, insecticides can also be toxic to humans, applying insecticides or consuming products treated with insecticides. On that score, the use of insecticides cannot be calculated just by the cost/benefit ratio in terms of the crop. 6 But compared to alternative uses in pest control, the benefits of insecticides still lead to accept the risks. Anyhow, a maximal output with minimal risks has not been achieved in most situations. Therefore alternative pest management technologies are the topic of this paper.

2.1 DDT and chlorinated hydrocarbons

DDT is one of the most popular or better unpopular insecticides. DDT

(dichlorodiphenyltrichloroethane) belongs to the group of chlorinated hydrocarbons, which are containing chlorine, hydrogen, carbon and sometimes sulphur and oxygen. Chlorinated hydrocarbons are the first widely used synthesized organic insecticides but due to environmental and human safety, their use has been restricted in most countries of the world. While insecticides of other groups are relatively unstable and broken down by enzymes in animals, in the environment of microorganisms, heat or ultraviolet light; 7 DDT, DDE TDE, dieldrin, aldrin, HCH and its isomers show high stability and fat solubility. This causes a phenomenon called biomagnification. Unable to be metabolized active pesticide residues are stored in nonlethal doses in the body fat of animals (e.g. cows) fed on plants treated with DDT. From there it gets to the humans body when fat-containing products (e.g. milk) are consumed. 8

5 cp.: Pedigo 1996, p.366

6 cp.: Gatehouse, Gatehouse 1998, p.212

7 cp.: Oregon State University 2007, http://oregonstate.edu/~muirp/pesthist.htm

8 cp.: Pedigo 1996, p. 381

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Besides mammals, also invertebrates fed on plants or detritus (such as predators) store DDT residues in their tissues. Facing the food chain in every ecosystem, rodents, fish, reptiles, amphibians and other insectivores are ingesting and concentrating the insecticide residues. Other top predators (e.g. hawks or owls) fed on these primary predators are yet accumulating higher doses of insecticide concentrations. Looking on the food chain from down to up, the total biomass is decreasing while the concentration of nonmetabolized pesticide residues increases. Thin eggshells and reproductive failures are the consequences, and lead to the decline of predators like ospreys, falcons, eagles, seagulls, pelicans and others. 9

2.2 Botanical insecticides

Botanical (= plant derived) insecticides are natural plant materials or products derived from plant materials. They have been used for centuries in tribal or traditional cultures before introducing to Europe and North America in the late 1800s. In the U.S., the application of botanical insecticides reached its peak in the 1960s. Thenceforward, a steady decrease took place. Today, they represent a very small part of insecticides annually used in the world. 10 Nevertheless a resurgence of botanical products seems to have a great potential because new effective and environmentally safe products have been discovered recently. Thereto novel synthetic insecticides can be developed from insecticidally active plant products. 11 The use of botanical insecticides declined with the discovery and increasing development of synthetic insecticides in the 1940s and 1950s. The newer synthetic organic insecticides were less expensive, longer lasting and more effective than the botanicals, which are expensive to extract, to test for environmental and human toxicity and generally impractical for commercial use. Botanical insecticides are no safer than the synthetics. 12 The word botanicals does also not imply that they are not toxic or “nonchemical”, botanical insecticides are toxic to pest and beneficial insects so that - if they are applied repeatedly - they have the potential to disturb the natural biotic control of pests by natural enemies. It would be adverse to consider plant-derived toxins as

9 cp.: Pedigo 1996, pp. 381-383

10 cp.: Weinzierl 1998, p. 101ff

11 cp.: Pedigo 1996, p. 385

12 cp.: Weinzierl 1998, p.102f

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harmless, although their limited persistence in the environment helps to minimize undesired effects. 13 Nonetheless botanical insecticides remain important in pest control for the following three main reasons:

1. “They sometimes provide the most effective control of insect pests that have

become resistant to other insecticides.

2. Most are short-lived in the environment, and they pose relatively low risks to

nontarget organisms, including the beneficial predators and parasites […], the higher level predators in food chains, and the human consumer of treated crops.

3. They are naturally occurring or derived or manufactured with minimal

technology, so they are sometimes accepted by organic certification programs or by certain consumer groups; they also may be more readily available than synthetic insecticide in developing countries.” 14 Therefore, botanical insecticides, as well as insecticidal soaps and oils, may be agents in biological control systems rather than conventional insecticides, although in practice, they are mostly not.

Currently, botanical insecticides of to plants are used for insect pest control. The first one is neem, extracted from the neem tree (Azadirachta india) and sold under the name Ornazin, AZA-Direct and Azatin. 15 Neem insecticides are acting as insect growth regulators. Therefore, neem will be discussed in chapter 4. The second one is pyrethrum, which is by far the most widely used botanical insecticide.

2.3 Pyrethrum vs. Pyrethroid

Pyrethrum is an extract from flower petals of Chrysanthenum cinerariefolium and the related species C. coccineum which are grown commercially in Kenya, where the flowers have highest concentrations of active compounds. 16 , Moreover pyrethrum daisies grow in Ecuador, and were once cultivated in Eastern Europe, the Middle East and Japan. 17

13 cp.: Weinzierl 1998, p. 103

14 Weinzierl 1998, p.101f 15 cp.: Cranshaw 2003, p.44 16 cp.: Weinzierl 1998, p.104 17 cp.: Casida 1973, Matsumura 1985 in Weinzierl 1998, p.104

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The active compounds of pyrethrum are called pyrethrins. These constituent esters are pyrethrin I and II, cinerine I and II and jasmolin I and II. Pyrethrin I and II, which are the pyrethrole ester of chrysanthemic (I) resp. pyrethric (II) acids, offer highest concentrations in pyrethrum. 18 Pyrethrins are contact poisons acting on the nervous systems. They are influencing the nerve transmission where they are slowing or preventing the shutting the sodium channels in nerve axons. 19 Mammals react with whole body tremors, insects are convulsing or hyperactive. 20 A few minutes after application, the insect cannot fly or move away. But a knockdown dose does not mean the killing of the insect population. Insect pests can recover because the natural pyrethrin is swiftly detoxified by enzyms. Therefore pyrethrins have been synthetically derived. The core chemical structure of synthetic pyrethrin, which is known as pyrethroid resembles natural pyrethrin. To improve features, such as persistence, synthetic pyrethrins have been modified to yield a more stable molecule. Carabamates, organophosphates or synergigsts may be added to delay the enzyme action and a lethal dose is assured. 21 This makes pyrethroids more toxic to humans and nontarget animals than natural pyrethrin. 22 But compared to conventional insecticides, pyrethroids are more effective and safe in application. That is why they are replacing many older insecticides and are the fastest growing group of modern insecticides. Currently, pyrethroids are categorized in four generations of development; the third and fourth-generation pyrethroids are the most widely used. Fourth-generation pyrethroids are the most potent. In comparison with third-generation pyrethroids, only one tenth of third- generation application rates in needed to achieve the same results. Even third- generation application rates are very low; while 1.1 to 2.3 kg of actual ingredient per hectare is needed using organophosphates or carbamates, only 0.11 kg of actual ingredient per hectare is needed to protect various crops using third-generation pyrethroids. 23 The advantages of synthetic pyrethrins are diverse. In contrast to natural pyrethrin, pyrethroids are able to induce quick knockdown effects and less recovery of poisoned insects. They are highly toxic to insects at very low rates and are broken

18 cp.: Weinzierl 1998, p.104

19 cp.: Bloomquist 1996 in Weinzierl 1998, p.104 20 cp.: Weinzierl 1998, p.104 21 cp.: Oregon State University 1994, p.1 22 cp.: Cranshaw 2003, p.42 23 cp.: Pedigo 1996, p.378

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down by ultraviolet light after 4 to 7 days. 24 The most factor important for the integration of pyrethroids in pest management systems is the economic advantage: pyrethrum is too expensive to use commercially and therefore mostly used as a household chemical. Pyrethroids are commercially used in agriculture, especially to maize, soybeans and cotton fields.

3 Biological control

“use nature as a partial ally, not as a total adversary” 25

Perkins 1996

Biological control is the oldest form of managing insect pests. Already in fourth- century China, ants were used by humans to suppress caterpillars and beetles in

citrus horticulture. 26

A natural enemy, like the ant in ancient China, feeds on the host or prey to extend its

own population at the expense of the pest population. Natural enemies are living organisms, which kill or weaken insects so that pest population number reduces. For many species, natural enemies are the main regulating force for their low population number. Other reasons can be unfavourable weather conditions or missing material requisites like food or nesting sites. Since nearly all insect populations are effected by natural enemies, the knowledge about natural enemies leads to the understanding of pest densities and the prediction of pest outbreaks.

Biological control is defined as the pest management tactic in which the manipulation of natural enemies leads to the reduction of a pest population. Different from natural control, biological control, or bio-control, does not implement other agents than

natural enemies, like the use of weather or food. 27

3.1 Natural enemies

In the theory of biological control, the pest population is seen as the perfectly density- independent factor which is regulated by the imperfectly density-dependent factor, the natural enemy. In a self-sustaining system, the pest population density is kept

24 cp.: Pedigo 1996, p.378

25 Perkins in Pedigo 1996, p.

26 cp.: Orr, Suh 1998, p.4f

27 cp.: Pedigo 1996. p.301f

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under the economic injury level, so that food supply and reproductive capability of the natural enemy is ensured without eliminating the pest which would include the death of the natural enemy as well. The changes in natural enemy numbers are called numerical response. When natural enemies destroy more pests per individual, a functional response has taken place. 28 Natural enemies of insects are diverse and include first of all insects themselves, but also vertebrates, nematodes, microorganisms and invertebrates other than insects. They are divided into parasites, parasitoids, predators or pathogens. The following description of these control agents is according to PEDIGO 1996. Parasites

A parasite feeds from the host it lives in or on, weakening or killing it. Insects,

nematodes and to a lesser extent mites are parasites with the greatest impact on insect pest populations. There are frequently many parasites in one specific part of the host.

Parasitoids

A parasitoid is an insect that parasitizes other insects or arthropods at any host

stage. A parasitoid is only parasitic in its immature stage. The free living adult lays its eggs inside the host or attaches them outside.

Parasitoids are the most effective agents in biological control because

- of their good survival,

- they only need one (or less) host for development,

- they survive on low host populations,

- their narrow host range leads to a good numerical response to host density. Nevertheless occur problems with parasitoids in biological control because

- weather and other forces reduce the host searching capacity,

- only the female are searchers

- the best searchers often lay few eggs,

- synchronization is often a difficulty.

The synchronization of the parasitoid life-cycle with that of the host is often interfered by adverse environmental conditions.

86 families in the orders Coleoptera, Diptera, Hymenoptera, Lepidoptera, Neuroptera

and Strepsiptera are known as parasitoids. Small parasitic wasps of the families Ichoneumonidae, Braconidae and Chalcidoidae are the most important parasitoids.

28 cp.: Pedigo 1996. p.303ff

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Besides these Hymenoptera, the Tachinidae of the order Diptera play a significant role in biological control.

Besides beneficial parasitoids, there are some that are nonbeneficial. Parasites living on parasitoids are a threat for the success of a biological control program. The phenomenon of a secondary parasite living on the primary parasite is called hyperparasitism.

Predators Predators are free-living individuals that feed on their prey in their immature and adult stages. Predators need more than one prey to reach maturity, often devouring the whole prey. Insect and mites have been the most successful predators in biological control, especially Coleoptera, Neuroptera, Hymenoptera, Diptera and Hemiptera. They are monophagus and oligophagus predators. In a group, predators are considered polyphagus as they tend to accept a wide range of prey. In terms of biological control, polyphagus species have the advantage that they survive low pest densities as they have the ability to move to alternate prey. This can be also a disadvantage when the predator does not suppress the growing pest population. The difficulty of control lies in the prediction of the density response from food availability alone. Biological control with predators has the advantage that

- predators kill their prey very fast,

- often immatures and matures of both gender are searching for the prey,

- synchronisation of predator and prey life-cycle is no difficulty.

Although parasitoids have been used more often than predators for biological control, it is impossible to predict the best natural enemy as it depends on the particular agroecosystem, the pest and the environmental circumstances. Hence, the best management tactics are those including predators and parasitoids as natural enemies.

Pathogenic microorganisms Pathogenic microorganisms are used as microbial insecticides that are often applied in a similar way to chemical insecticides. Microorganisms with impact on insect pests are bacteria, viruses, protozoan and fungi. Mostly bacteria, fewer viruses and fungi are used for pest control as they kill insects very quick. The spore-forming bacteria are the most important species, particularly the genus Bacillus. The disadvantage of the most successful bacteria (Bacillus popilliae and B. lentimorbus) is that it is difficult and expensive to propagate them in vitro.

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Future advances in biotechnology should allow a modification of fastidious microbial pathogens for easier reproduction. Also the propagation of host-insect tissue from single cells is expected. The expansion of the killing spectrum and improved environmental stability through biotechnology has already been applied on Bt by Ecogen Inc. and Mycogen Corp. The use of Bt as part of genetic engineering will be further discussed in chapter 5.

3.2 Biocontrol of cassava pests

The following case study aims to portray a typical African crop, one of its pests and biological methods to control it.

The cassava host plant Cassava (Manihot esculenta) was introduced to Africa by the Portuguese who took it from South America. It penetrated into the interior of the continent only in the 20 th century but quickly became popular as adaptation has never been a problem. Cassava grows on poor soils and can endure prolonged drought and is easily propagated by its offshoots. Compared to other food crop in Africa, it gives the highest output on the lowest input. Cassava is the crop of the poor. It is the main staple food for about 200 million Africans, particularly in the poor countries. 29 For centuries cassava has been relatively free from insect pest in Africa. Endowed with a high cyanide and latex content in stem, leave and tuber, it has high natural plant defences and was little attacked by arthropods in Africa, whereas in South America co-evolved some 200 insects feeding on cassava. The situation changed dramatically when in the early 1970s two pests invaded simultaneously the African continent. The cassava mealybug was inadvertently introduced into to Republic of Congo and D.R. Congo (former Zaire) in 1973; the first outbreaks of cassava green mite pest were in Uganda. Both pests had been introduced by illegally imported plant material from South America and quickly spread across almost all the African continent. 30 In West Africa it spread at 300km -1 per year, natural barriers like the Rift Valley decelerated the spread of P. manihoti in East Africa. 31 Within 20 years, nearly the entire cassava belt 32 was infested by the cassava mealybug. P. manihoti became the number one pest of cassava on the continent, severely affecting the livelihood of 29 cp.: Lundborg 1999 p.22

30 cp.:Neuenschwander 2003, p.45

31 cp.:Herren, Neuenschwander 1991, p.259

32 Main exceptions are Madagascar and the Indian Ocean Islands

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poor people. 33 The losses of the farmers are estimated to be in the range of US$ 2 billion per year, cassava prices of 1999 were five times higher than two years ago. 34 The cassava mealybug Since the practice of biological control requires a comprehensive study of the organisms involved in the control program, this chapter gives a short overview of the main characteristics and the ecology of cassava mealybug.

Mealybug is the common name for insects of the Pseudococcidae. This family of unarmored scale insects is found in warm, moist climates. The Mealybug is soft- bodied with no outer shell like other scale insect families (e.g. Diaspididae). They are covered by a white waxy powder. Pseudococcidae have filamentous projections around the perimeter. 35 Being sexually dimorphic, female mealybugs are wingless; they exhibit reduced morphology and nymphal characteristics while males have wings and change their morphology during their lives. Like other Homoptera, mealybugs are hemimetabolous insects, meaning that they do not undergo a complete metamorphosis. However, male mealybugs pass a radical change during their life cycle, changing from wingless, ovoid nymphs to flying adults. 36 Mealybugs are considered as pests because of feeding from plant juices of greenhouse plants, house plants and subtropical trees. The females are responsible for the name mealybug because of secreting a powdery wax layer to protect their environment while sucking plant juices. As adults, the males do not feed at all; their short-time adult stage is for fertilizing the female. 37 The most destructive pests are the cassava mealybug and the mango mealybug (Rastrococcus invadens). The cassava mealybug (Phenacoccus manihoti; Homoptera, Pseudococcidae) is a pathenogenic insect with three nymphal instars. It is subsisting from Manihot spp., where it colonizes the cassava tips, but also found on other plants infrequently. 38 The cassava mealybug population size has its optimum in the dry season. Owing to the washing effect of the rain and the renewed growth of the cassava tips, cassava mealybug populations collapse during the rain season. When the plant substrate becomes unacceptable, it also occurs that the population drops even before the rainy

33 cp.:Neuenschwander 2003, p.46

34 cp.:Lundborg 1999, p.22 35 cp.:IPM of Alaska: 2005 www.ipmofalaska.com/files/mealybugs.html 36 cp.:Jahn, Beardsley 1998, p.73 37 cp.:Jahn, Beardsley 1998, p.74f 38 cp.:Herren, Neuenschwander 1991, p.262

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season starts. Dispersal over long distances is by animals and humans. Cassava mealybugs move with crawlers that are picked up by air currents. Also human spread P. manihoti by transporting infested plants. 39 Mealybugs are found in warm, moist climates 40 , the cassava mealybug has a low thermal threshold of 14,7 °C and shows no development above 36 °C. The optimal temperature is about 28 °C. All life table parameters differ from plant varieties, but not by the leaf age. The net reproductive rate is about 500 eggs, on stressed plants, all life table parameters are marginally better. 41 Most mealybugs are stunting the roots of their host plant 42 . P. manihoti is attacking the cassava tips to suck plant sap with its mouthparts 43 . The shoot tips get stunted, leaf distortion, yellowing and total leaf loss are damage symptoms of stunted plants 44 . Due to the stop of leaf production, carbohydrates cannot be accumulated in the tuber ceases. The early mobilisation of sugars causes results in severe quality decline of tubers. Beside the loss of tubers and leaves for alimentation, contorted stems become useless as planting material. 45 The progress of biological control The outstanding biological control program of the International Institute of Tropical Agriculture (IITA) to control cassava pest in African agriculture, exemplifies the different steps towards the implementation of biological control.

With the financial aid from the International Fund for Agriculture Development, the IITA, headed by Hans Rudolf Herren in 1980 and 1981, initiated the Africa-wide Biological Control Project (ABCP). The IITA Biological Control Program developed a control strategy that began with the systematic exploration of the origins of the pest. The second step was the rearing of the most promising natural enemies and their taxonomic and biological characteristics as well as ecological impacts. After that, the release of the selected natural enemies in Africa was started. The study also included an analysis of the socio-economic impact of the pest. 46 Polyphagus and oligophagos predators and parasitoids attack the cassava mealybug, They found a new food source when the cassava mealybug appeared in

39 cp.: Herren, Neuenschwander 1991, p.262

40 cp.:Jahn, Beardsley 1998, p.74f 41 cp.: Herren, Neuenschwander 1991, p.263 42 cp.:Jahn, Beardsley 1998, p.74f 43 cp.:Herren, Neuenschwander 1991, p.262 44 cp.:IPM of Alaska 2005 www.ipmofalaska.com/files/mealybugs.html 45 cp.: Neuenschwander 2003, p.47 46 cp.: Herren, Neuenschwander 1991, p258

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Africa. 20 species are common in Africa and were identified to have some impact. Coccinellid are important predators. They occur when the cassava mealybug infestation is high but suffer from high parasitism. Other predators are the host- specific cecidomyiid Didrodiplosis manihoti and the lycaenid Spalgis lemolea, which occur unsteady. A few indigenous Hymenopterus parasitoids of the genus Anagyrus were found as well. 47 After the detection that the Phenacoccus manihoti in an invasive species which has its origin the Neotropics, several researches started in South America to explore natural enemies of P. manihoti. The parasitoids that were found on what researchers thought to be P. manihoti, did not reproduce on mealybugs in Congo and former Zaire because of misidentification of the cassava mealybug, which was not P. manihoti. After 30 years of research on cassava in the Neotropics, P. manihoti was finally identified in Paraguay in 1981 by A. C. Bellotti, working for the Centro International de Agricultura Tropicana (CIAT). Following explorations showed that the cassava mealybug has its origins in the Paraguay River basin where P. manihoti populations there are low and unsteady. 48 It was Dr. Maajid Yaseen, principal entomologist of the Commonwealth Institute of Biologiacl Control (CIBC), who discovered the parasitoid, which was selected for the use in the biological release program. The encyrted parasitoid Epidinocarsis lopezi is a parasitoid wasp which lays its eggs inside mealybugs where the larva feeds on the intestines, killing the bug. 49 In addition to that “star enemy” 50 , the coccinellid predators Hyperapsis raynevali, H. notata and Diomus spp were introduced as well, but played a marginal role compared to the principal agent E. lopezi. Even many other predators and parasitoids became less abundant after the distribution of the exotic parasitoid. 51 E. lopezi became the most important parasitoid, wherever it was established.

Epidinocarsis lopezi Desantis (Hymenoptera: Encyrtidae) has some special characteristics that made it an effective biocontrol agent:

Due to the shorter generation time compared to the host, its population has the capacity to grow larger than that of the mealybug. Besides host-feeding and the ability for mutilation, E. lopezi prevents the successful reproduction of the mealybug –

47 cp.: Herren, Neuenschwander 1991, p.263

48 cp.: Herren, Neuenschwander 1991, p.260f 49 cp.: Lundborg 1999 p.23 50 Lundborg 1999 p.23 51 cp.: Smith, Bellotti 1996, p.6

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if it is not killed directly. Because of its high specificity, searching and dispersal capacity, it survives even in case of low host population densities. This way, E. lopezi fills an ecological niche without competition less specialized competitors. In addition, E. lopezi shows density-dependent aggregation and reproduction on most host population densities. 52 These features are not given the other tested natural enemies so that E. lopezi was selected for the cassava mealybug control in Africa and successfully did.

By 1987, eight of the 18 species of natural enemies that were found in the distribution area of cassava mealybugs, were sent to England where rearing and host specificity tests were done by CABI Bioscience. After the multiplication by the IITA in Ibadan (Nigeria) and later in Cotonou (Benin), the first natural enemies of P. manihoti were exposed in Nigeria and later send to various other African countries. Within three years, parasitoids has spread over 200 000km 2 in southwestern Nigeria. Until end of 1985, over 50 releases in 12 African countries has been done, by 1990 E. lopezi covered an area of more than 12.7million km 2 consisting of 24 countries. The parasitoid established in all ecological zones that were infested by the mealybug. Currently, the mealybug no longer poses a threat to most cassava growing regions in

30 African countries. 53

The biological control over cassava pest has shown great success in ecological and economical matters.

Cassava yield losses decrease gradually by 10% during the first year to 90% in the fifth year. In an economic sense, a cassava yield worth $1.7 billion will be saved after the eighth year. 54 In the savannah a great reduction of stunted cassava tips from 88% to 3% has taken place, the cassava yield increased by 2500kg/hectre compared to areas were E. lopezi had not been established yet. 55 SCHAAB 1996 estimated the costs and benefits of the whole program from 1974-2013 to $49 million and $9.4 billion so that, depending on the scenario, the cost/benefit ratio ranges between 1:170 and 1:431. NEUENSCHWANDER and HERREN 1991 estimated a cost/benefit ratio of 1:149 which would still be enormous compared to alternative pest control strategies mentioned in the previous chapters.

52 cp.: Herren, Neuenschwander 1991, p.266

53 cp.: Neuenschwander 2003, p.48

54 cp.: Lundborg 1999, p.23

55 cp.: Smith, Belloti 1996, p.6

17

The $49 million required for exploration, biological studies, mass rearing, release and impact studies is a one-shot investment. Once the natural enemies are established, a natural balance between them and the host will follow so that no continuous costs for the farmers are emerging. The case study showed that the classical approach to biological control can be a very successful method for the control of serious insect pests in African agriculture. IITA’s Africa-wide Biological Control Project, under the direction of Hans Rudolf Herren, who was awarded the World Food Price for in 1995, not only saved one of Africa’s major staple crops and farmers billion of dollars, but demonstrated a reliable method of controlling serious insect pests on an international level. The success of the program gives a momentum necessary for future programs to manage other pests like the maize stem borer or insects on cowpeas via biological control. As several exotic pests have invaded and in future times probably will continue invading the African continent, the use of exotic parasitoids and predators will be necessary. The establishment of invasive species always requires a comprehensive study of the plant to be saved, the pest and its natural enemies, the agrosystem and ecosystem to inhibit the threat of imbalances or undesired long-term consequences.

4 Insect growth regulators

Besides the proved success of managing pests by methods of biological control, a lot of anticipation is placed in the use of insect growth regulators to control insect pests. This chapter demonstrates the function and impact of insect growth regulators on insect pests and gives an idea of their use in pest management systems.

Insect growth regulators are pesticides that mimic the action of hormones on the growth of insects. 56 The insect’s developmental physiology is regulated by hormones produced by endocrine glands. Molting and metamorphosis are regulated and initiated by brain hormones, ecdysone and juvenile hormones. Brain hormones are secreted by neurosecretory cells in the location of the pars intercerebralis. After linkage to environmental stimuli with other hormone systems, the brain hormones get in the blood. This causes the stimulation of the prothoracic gland which secretes ecdysone. The result is that the insect molts. The concentration of the juvenile hormones from the corpora allata in the blood is the determining factor for the body form of the

56 cp.: Cranshaw 2003, p.44

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insect. A larva at full growth with a complete metamorphosis has a reduced concentration of juvenile hormones, in the next molt the pupal form emerges. The decreasing concentration of juvenile hormones allows the active growth of imaginal disks. These cells have the potential the express the adult character in the following molt. In a gradual metamorphosis, juvenile hormones reduce gradually so that in the absence of juvenile hormones the adult stage emerges. Juvenile hormones can also have reproductive functions influencing ovary development and egg yolk production. Furthermore, juvenile hormones can stimulate diapause, behaviour, communication, caste differentiation and morphogenesis. 57 As described above, juvenile hormones play a prominence role in the insect life cycle. Through the interaction of hormone agonists and antagonists, growth and metamorphosis can be stimulated. Insect growth regulators offer great potential because of disrupting life processes that are unique to the insects.

Besides these chemicals disrupting metamorphosis there have been also developed chemicals hat are modifying insect’s behaviour. Both are working on systems that vertebrates do not have. Hence they seem to be a safe alternative to conventional insecticides, which have no selective activity. 58 Already mentioned in chapter 2, conventional insecticides affect the insect’s nervous system. Facing that insect’s nervous systems function in the same way like other animal’s nervous systems do, conventional insecticides got a broad poisoning power. The use of these chemicals is hazardous as it can cause harm to nontarget organisms. Insect growth regulators are often attacking only one specific group of insects. 59 For example Lepidoptera show minimal toxicity for beneficial predators and parasitoids. 60 First generation insecticides are the stomach poisons, second-generation insecticides are contact poisons. Due to environmental safety and advanced development, insect growth regulators (IGRs) are described as third-generation insecticides. They are applied with insecticide equipment on a specific area. Different from conventional insecticides, timing is more important and a limiting factor, considering that IGRs can only function on immature insects. 61 Due to this insect’s stage sensibility, it is difficult to achieve a rapid breakdown of the insect pest population and pest presence or levels of injury must be tolerated longer than with

57 cp.: Pedigo 1996, p.456f 58 cp.: Pedigo 1996, p.455 59 cp.: Cranshaw 2003, p. 44 60 cp.: Beckage 1998, p.123 61 cp.: Pedigo 1996, p.455f

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conventional insecticides. This disadvantage can be avoided by using compounds that have a longer in-vivo half life, so that it remains in the body until the insect’s sensibility to IGRs is high. Disrupting the metamorphosis, juvenile hormone antagonists are used for long-term control, whereas ecdysone antagonists cause an unsuccessful molt within 24h. The antifeeding effects of azadirachtin show up

immediately, leading to disruption of molting. 62

4.1 Juvenile hormone agonists

Juvenile hormone agonists are highly effective IGRs causing a wide range of development disturbances. Impacts on susceptible insects are disturbance of embrogenesis, larval development, metamorphosis and reproduction. Compounds of juvenile hormone agonists are the terpenoids methoprene and hydroprene as well as

the nonterpenoids fenocxycarb and pryproxyfen. 63 Azadirachtin Azadirachtin is a tetranortriterpenoid found in the seeds of the Indian neem tree (Azadirachta indica). This plant is for long time known as source for pharmaceuticals

in Asia and Africa. 64 Neem seed extracts contain besides oils several compounds affecting insect development. The most important is azadirachtin. This biological insecticide has a strong antifeedant and repellent activity and shows pleiotropic effects on growth, development and reproduction on chewing and sucking phytophagous insects and stored product pests. More than 200 species are susceptible, including aphids, lepidopterans, hemipterans, cockroaches, beetles and orthopterans. Azadirachtin is translocated into the tissues of infested plants, but can also reach insects via the leaf surface or by direct contact. It also works in water, affecting aquatic species like mosquitoes. The affected insects often die during a

molt, usually a week or longer after treatment. 65 The slow effects and narrow range of susceptible insects are the main disadvantages of neem insecticides. Azadirachtin has shown excellent selectivity, it has minimal effects on nontarget arthropods and no adverse effects on fish and livestock have been detected. There are no environmental effects because residues are broken

down in sunlight and rainfall. 66 Although this fact makes it safe in use, neem’s field

62 cp.: Beckage 1998, p.124

63 cp.: Beckage 1998, p.127 64 cp.: Cranshaw 2003, p.44 65 cp.: Beckage 1998, p.129ff 66 cp.: Pedigo 1996, p.456

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performance has failed in many pest control uses because of low persistence and and limited effectiveness in the presence of rain or sunlight. 67 Nevertheless, its use is highly recommended because of the broad-spectrum control and very low toxicity. 68 Terpenoids Methoprene and kinoprene Methoprene is affective on Diptera, Siphonaptera, Coleoptera and some Lepidoptera and Homoptera. 69 Sold under the name Altosid®, it is used against mosquitoes and horn flies (Haematobia irritans) attacking cattle. 70 It disrupts the embryogenesis and egg hatch. Mosquitoes are killed as larvae and as pupae, preventing the rotation of the male genitalia. In houseflies and other Diptera, methoprene adverts adult emergence. Maggots of the horn flies that feed on cattle dung are killed by methoprene that is administered to animal food. 71 Administered on Lepidoptera, it causes molting to supernumerary instars and formation of intermediates. Kabat® is sold to suppress Coleoptera and Lepidoptera and in stored tobacco. 72 In African cotton farms, as well as in other parts of the world, methoprene is widely used because of enhancing silk production in silk worms (Bombyx mori). Methoprene and also fenoxycarb applied during summer season are helping to get improved cocoon yield. Prolonging the larval life of insects, these two juvenile hormones analogues cause improved quantitative and qualitative parameters of cocoon and silk like cocoon and shell weight, silk filament length, winding capacity or tenacity. 73 Kinoprene is attacking Homoptera, such as whiteflies. 74 Fenoxycarb and pyriproxyfen Fenoxycycarb and pyriproxyfen are nonterpenoidal juvenile hormones that have recently appeared on the market and have been very successful because of greater stability in the environment, compared to the terpenoid juvenile hormone agonists. Fenoxycarb causes sterility, death of insect eggs, permanent larvae, and formation of nonviable intermediates. It interferes with metamorphosis and affects caste differentiation. The non-neurotoxic carbamate shows activity on a wide range of

67 cp.: Weinzierl 1998, p.112

68 cp.: Cranshaw, p.44 69 cp.: Beckage 1998, p.127 70 cp.: Pedigo 1996, p. 460 71 cp.: Beckage 1998, p.128 72 cp.: Pedigo 1996, p. 460 73 Mamatha et al 2006, www.academicjournals.org 74 cp.: Beckage 1998, p.128

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insects, including Heteroptera, Lepidoptera, Hymenoptera, Coleoptera, Diptera, Dictyoptera, Isoptera, and Homoptera.

Besides inducing permanent larvae in the silkworm (B. mori), it successfully inhibits the development of the parasitoids Phanerotoma ocularis and Pseudoperichaeta nigrolineata.

Other IGRs, such as methoprene also have impact on the emergence and methamorphosis of parasitoids, but the effects seem less detrimental compared to the effects of conventional neurotoxis pesticides. 75 Another potent juvenile hormone agonist is pyriproxyfen. It is active on a wide range of arthropods including ants, fleas, mole crickets, mosquitoes, flies, whiteflies, scales, cockroaches, ticks as well as Lepidoptera. Like methoprene, it hinders the emerge of horn flies, face flies and house flies from dung of cattle or other animals fed with pyriproxyfen. Pyriproxyfen can also be applied directly on the horn fly. Like the other juvenile hormone agonists discussed above, pyriproxyfen has multiple impacts on a single species. Applied on the desert locus (Schistocerca gregaria), it disrupts embryogenesis and metamorphic molt and leads to morphological deformities. 76

4.2 The practice of IGRs

The mentioned examples have shown that IGR have a wide range of application against insect pests. For the effective implementation of IGR such as juvenile hormones, which are thought to be the most appropriate for the control of insect pests, STAAL 1975 has set certain requirements. The conditions, under which the pest management should be applied, must include at least one of the following:

1. “Larvae of the pest species do not cause damage; only the adults are

perceived as harmful or nuisance.

2. Individual insects or low numbers are not harmful; only large populations that

expand through several short population cycles are significant (greenhaouse Homoptera, stored product pests, and mushroom pests).

3. Environments where applied have a high degree of protection against

breakdown factors, particulary sunlight (most applications).

4. Environments are enclosed and thus protected against massive reinfestations

(stored products, greenhouses).

75 cp.: Beckage 1998, p.128

76 cp.: Beckage 1998, p.129

22

5. Sedentary insect targets (low mobility) are not likely to resurge quickly

because of reinfestation (scale insects, mealybugs).

6. Special instances exist in which the safety of the compound and the lack of

other control methods are the prevalent considerations (pharaoh ant [Monomorium pharaonis]).” 77 This conditions required show that juvenile hormone agonists are most appropriate where the infestation is from insects pests with short life cycles and enclosures protect residues. In addition, there should be no need for immediate control and a low number of infections can be tolerated.

Facing the selective activity among insects, often specific to one family or one group of insects (for example caterpillars), the use of IGRs is compatible with the activity of natural enemies of insect and mite pests. 78 It can be concluded that IGRs are an acceptable modern pest management technique, offering a compromise in selectivity between the less desirable extremes of narrow specificity and broad-spectrum activity. The selective requirements are satisfied so that a widely integrated use of IGRs and especially juvenile hormone agonists in IPM tactics can be expected in the future.

5 Biotechnology

Biotechnology is the latest strategy to manage insect pests. The use of biotechnology in various areas affecting human beings life is currently on of the most discussed topics. To set an example for the use of biotechnology, this chapter provides vital information about biotechnology and its achievements with Bacillus thuringiensis. The Convention of Biological Diversity defined in 1992 the term biotechnology as “any technological application that uses biological systems, living organisms, or derivatives thereof to make or modify products or processes for specific use”. 79 In the media, the term biotechnology is represented in many different ways and meanings. Biotechnology is a technology that implies:

“1. genetic engineering for producing vaccines and improving plants and animals,

2. monoclonal antibodies for diagnosis of cell proteins,

3. new cell and tissue techniques for rapid propagation of living cells.” 80

77 cp.: Staal 1975, Pedigo 1998, p. 460f

78 cp.: Cranshaw 2003, p.44

79 cp.: World Foundation for Environment and Development 2004 http://www.wfed.org/resources/glossary/

80 Pedigo 1996, p.441

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In agriculture, biotechnology gives hope to solve many insect pest problems by the development of new plant cultivars resistant to insect pests. Even though the revolution in plant breeding and wide-scale mechanism of agriculture have brought high yielding crop varieties and have protected the developed world from food shortage, still famines and chronic shortages of calories supply are present in the developing world.

As demonstrated before, the indiscriminate use of pesticides is a not sustainable agriculture practice in the long term. Many insects have become resistant to pesticides and have become even a greater problem than it was before the pesticide was introduced. Therefore, a number of less harmful pesticides and methods of biological control have been developed. Still, they do not give such high levels of return on a short term level. As demonstrated in the example of managing the mealybug pest on cassava, it took several years to achieve a reduction of pest infestations.

For these reasons, genetic engineering for insect resistance of crops has been enthusiastically adopted by government authorities and the agricultural industry. 81 It is asserted that new transgenic crops will reduce pesticide use and increase productivity – “a promise that developing countries desperately want to believe”. 82 Biotechnology allows the extension of the gene pool available to a specific species. Genetic engineering of natural enemies of insects and mites by using recombinant

DNA technology currently includes viruses, protozoa, predators and parasitoids and

insect pathogens, such as bacteria. 83 At present, resistant plants are developed by inserting the gene responsible for producing delta endotoxin into the plant genome. This gene comes from the insect pathogen Bacillus thuringiensis. 84

5.1 Bacillus thuringiensis

Bacillus thuringiensis (Bt) is a soil dwelling bacterium that also occurs on some plant surfaces and in caterpillars of some moths and butterflies. Upon sporulation, Bt forms a crystalline protoxin protein (cry toxin). The cry toxin is encoded by the cry gene carried on a plasmid within the bacterium. Cry toxins have specific activities against species of Lepidoptera, Diptera and Coleoptera. When these insects ingest the spores, the protoxin is cleaved and active Bt toxin molecules are generated. After 81 cp.: Gatehouse, Gatehouse 1998, p.213

82 Kuyek 2002, p.1

83 cp.: Harrison, Bonning 1998, p.244

84 cp.: Pedigo 1996, p.443

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binding to a specific glycoprotein receptor on the epithelial cells, the toxin inserts itself into the gut cell membrane. There, the bound toxin causes ion channels in the cell membrane of the gut epithelial cells. The free passage of ions leads to an imbalance of ion concentration. The result is the death and lysis of the cells lining the gut, leading rapidly to the insect’s death. The carcass serves as a substrate for the growth of Bt. After sporulation, fresh spores get into the soil so that the cycle is completed.

Thus, Bt serves as an important reservoir of Cry toxins and cry genes for production of biological insecticides and insect-resistant genetically modified crops. The use of Bt preparations (mostly sprays) as an conventional insecticide is very limited. The proteins quickly break down in ultraviolet light and the spray is washed from the plant surfaces in wet weather. But the high toxicity of Bt toxin protein, together with the easy task of isolating the encoding gene made Bt evident for the development of transgenic plants. 85 Currently, there are many discussions about the use of the genetically modified maize, which “will benefit African farmers through increased yields and disease resistant crops” 86 , says biotechnology stakeholder AfricaBio. Therefore, the following case study demonstrates the current discussions concerning the use of bt maize to control insect pests in Africa.

5.2 Management of maize pests in agribusiness

As the focus of previous described pest management systems was given to the practical application, this chapter wants to portray the maize pest with emphasis on the decision-making forces behind pest management.

Maize (Zea mays L. spp. mays) is the second most important food crop in Africa. 95% of total maize production is done by small and medium scale farmers across the whole continent in different ecological conditions. 87 Besides a number of environmental factors like droughts or soil fertility, various insect pests are main constraints to farmers, who grow maize in resource-poor systems. About 20-40% of the potential yield can be decimated by the larvae of certain moths: cereal stemborers. 88 The ICIPE (African Insect Science for Food and Health) even

85 cp.: Gatehouse, Gatehouse 1998, p.214f

86 Venter 2005 http://www.africabiotech.com/news2/article.php?uid=129

87 cp.: DeVries; Toenniessen in Kuyek 2002, p.12

88 cp.: Kuyek 2002, p.12

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estimates to yield losses in chronically infested areas between 10-70%. 89 Gramineous stemborer pests occur in nearly every maize cropping 90 and are therefore considered to be the most damaging insect pests 91 . The various species of cereal stemborer pests in Africa are all indigenous, except Chilo partellus, which invaded the continent from Asia. In 1930, it was first found in Malawi, from where it spread over whole East and Southern Africa, at times displacing indigenous species. Chilo partellus quickly became the most injurious pest for maize and sorghum. 92 But still, indigenous stemborers have an economical importance throughout the continent as their occurance is depending on the elevation. In West Africa the pyralids Eldana saccharina and Mussidia nigrivenella and the noctuids Sesamia calamistis and S. botanephaga occur most frequent. The noctuid Busseola fusca is the main pest in Cameroon and Central Africa, prevalent in all altitudes, while in East and Southern Africa, it causes economic injuries in areas above 1000 meters above sea level. The crambid Chilo partellus has economic importance in both lowlands and mid-altitudes and is moving up to higher altitudes. 93 At present, 50% of all maize plantations in developing countries show insect pest infestations, alone in Kenya, stemborers allayed the ultimate harvest of 15%. 94 The introduction of genetically modified maize seems to be an easy solution to get out of this regression. Crylab, a bt gene that have been introduced into maize and commercially released in the U.S., is proven to be effective against African insect pests. African farmers who used bt maize have seen increased yields with lower inputs of pesticides. The decreased health risks together with increased yields and incomes, must outweigh the risks of the new technology, affirms KANAMPIU 2002, stressing the easy method of application as African farmers “prefer their inputs being in the form their most used to – the seed and not insecticides“. 95 Proponents of biotechnology are claiming that bt maize will relieve hunger around the world. But does bt maize really meet the needs of the vast majority of African small scale farmers? Who is interested in the introduction of bt maize in Africa? Facing the global importance of maize production, it is not surprising that stemborer pest control became a major interest for agribusiness. The industry focussed in

89 cp.: ICIPE 2006 http://stemborer.icipe.org/ 90 cp.: Kuyek 2002, p.13 91 cp.: Youdeowi in Overholt et al 1996, p.1 92 cp.: Overholt at al 1996, p.1 93 cp.: ICIPE 2006 http://stemborer.icipe.org/ 94 cp.:Kanampiu 2002, p.108 95 cp.:Kanampiu 2002, p.108

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particular on the incorporation of bt-gene. All bt maize is sold by large seed Trans National Corporations (TNCs) who also hold the patents on the relevant technologies. In South Africa, where in 1999 over 50 000 hectars of bt maize were planted; the market for transgenic seeds is controlled by the seed TNCs Monsanto, Pioneer Hi-Bred and Pannar. 96 Transnational pesticide corporations are pushing genetic engineering into agriculture by investing in agricultural biotechnology. The buyout of seed companies and financing Research and Development (R&D) secures the monopoly over the control of genes and leads to privatisation of biodiversity. Private and public sector have become allies of the industry that will spread their technologies throughout Africa. Merchandising genes is an industrialist’s interest but does not meet the needs of most African subsistence farmers. 97 The bt maize sold by the TNCs has been incorporated in maize varieties for commercial use and are therefore not suitable for small scale farmers with no market access. Pioneer Hi-Bred runs a program for such subsistence farmers, but without a specific breeding program designed for that area, where the bt hybrid maize was introduces for “philanthropic reasons” 98 . Private and public sector did little research into maize for small scale farmers. For the mid-altitudes of Kenya, where small farmers grow 40% of Kenyans maize, no adapted variety has been developed by the public sector. The Kenya Agricultural Research Institute (KARI) focussed on the high potential lands, where cash crops are grown on big farms.

This case from Kenya is not a single one which demonstrates that governments are not meeting the needs of small farmers.

Fact is that small farmers have already developed cultural control techniques to fight pest infestations. Additionally direct applications such as neem or pyrethrum have shown success in pest management. In the case of maize infestations with stemborers in Kenya, biological control strategies have shown that the infestation rate can be reduced by 53%. In 1991, ICIPE has released the natural enemy of Chilo partellus on different sites in Kenya. The result was that not only the exotic stemborer could be controlled by the parasitic wasp Cortesia flavipes Cameron (Hymenoptera:

96 cp.: Mwangi, Ely 2001, www.biotech-monitor.nl/4803.htm

97 Cp: Kuyek 2002, p.14f

98 Kuyek, 2002, p.13

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Braconidae), but also three other stemborer varieties were attacked by the exotic parasitoid. 99 Concluding that great achievements has already been done in the development of genetically modified crops to control insect pests in the far future, genetically modified crops will not solve the fundamental problems affecting African small farmers. If so, the root causes of poverty, which lay in land distribution, market constraints and affordable technologies and practices that work with on-farm resources, such as soil and water management, biodiversity conservation strategies and mixed cropping systems would be addressed.

6 Conclusions and prospectus

With the beginnings of agriculture people suffered from crop losses due to insect pests and developed various tactics and techniques of pest management. After World War II, the use of conventional insecticides such as DDT was thought to be the solution to eliminate any insect pest. Indeed, pesticides are pre-eminent on their short-time effectiveness, but on a long term the use of pesticides resulted in the direct opposite. Not only insecticide resistance, pest resurgence and pest replacement were the effects; as DDT and related pesticides do not easily break down in the environment, they accumulated in the food chain and spread throughout ecosystems with devastating effects. While conventional pesticides are therefore not suitable for the integration in pest management systems, botanical insecticides quickly break-down in the environment and show lower risks to nontarget organisms. Especially in African developing countries botanical insecticides may be potential control agents as they are naturally occurring and minimal technology is needed for production. But as the comparison between natural pyrethrin and synthetic pyrethroid has shown, the use of botanical insecticides in the practice is limited to the non commercial use while pyrethroids have been established on commercial crop fields. The third generation of insecticides are insect growth regulators. While most pesticides are acting on any nervous system and are therefore toxic to nontarget organisms, insect growth regulators provide environmental safety and high specificity. Juvenile hormone agonists have been widely used to control different pests such as the desert locus, or even enhanced silk production in Africa. Therefore,

99 cp.: Overholt at al 1996, p1ff

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IGRs are highly recommended for Integrated Pest Management because of compatibility with the activity of natural enemies.

The practice of biological control has currently proven to be a successful method to manage pests on the long term. The cassava mealybug, which had become a serious pest throughout the African cassava belt, is nowadays controlled by the Africa-wide establishment of the parasitoid Epidinocarsis lopezi. Different from the application of insecticides, biological control provides a reliable mechanism of pest control by the same time offering an excellent cost/benefit ratio.

Another way to face insect pests is the development of insect-resistant plants by using recombinant DNA technology. Bt maize may be able to fight serious maize pests in African agriculture systems, like the stemborer Chilo partellus. But in a political sense, genetically modified crops do not pose a sustainable method to control insect pest as the use of genetically modified crops is causing unpredictable risks for environmental and human wellbeing. From the viewpoint of African small scale farmers, the use of genetically modified crops additionally creates new dependencies on a socio-economic level in the way that the negative impacts outweigh the suspected benefits. Therefore, genetically modified crops in African agriculture are neither supporting the empowerment of farmers nor following the concept of IPM to be user-orientated.

It has been figured out that various strategies have been developed and applied to control insect pests; all of them seem to have specific advantages as well as disadvantages. The paper has shown that in recent years, the focus of controlling pests has been either on short-term or/and single technology interventions. The biological control program to fight the cassava mealybug for instance, has replaced the use of chemical by another single technology. Strategies of pest management are still dominated by a single technology (e.g. biological insecticides, IGRs or biological control) instead of implementing Integrated Pest Management systems in its true sense which means the break away from the search for the “magic bullet”. Only a combination of different tactics and techniques can address the problems of sustainable agriculture.

No matter which methodological or technical advances in improved food production are identified to become part of IPM, effective implementation with social and economical benefits for African farmers will only be assured by appropriate economic and political support.

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Truly integrated pest management is the only answer to fight food insecurity in its roots which means the reduction of poverty. The eradication of extreme poverty and hunger and an ensured environmental sustainability are point 1 and 7 of the Millennium Development Goals. If the United Nations want them to be realized by 2015 they have to take in account that the implementation of IPM has to become a major subject. So far, the realization of Integrated Pest Management remains one of the most challenging goals to achieve a sustainable food production on a global level.

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Ehrenwörtliche Erklärung

Hiermit versichere ich, dass ich die vorliegende Arbeit selbstständig und ohne Benutzung anderer als der angegebenen Hilfsmittel angefertigt habe. Alle Stellen, die wörtlich oder sinngemäß aus veröffentlichten und nicht veröffentlichten Schriften entnommen sind, sind als solche kenntlich gemacht. Die Arbeit hat in gleicher oder ähnlicher Form noch keiner anderen Prüfungsbehörde vorgelegen.

Bayreuth, den

---------------------------------------------------------------------- Anne Hegge

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