Seminar Paper, 2007, 35 Pages
1.1 Theory and Tactics of Pest Management
2 Conventional insecticides
2.1 DDT and chlorinated hydrocarbons
2.2 Botanical insecticides
2.3 Pyrethrum vs. Pyrethroid
3 Biological control
3.1 Natural enemies
3.2 Biocontrol of cassava pests
4 Insect growth regulators
4.1 Juvenile hormone agonists
4.2 The practice of IGRs
5.1 Bacillus thuringiensis
5.2 Management of maize pests in agribusiness
6 Conclusions and prospectus
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.
There are various approaches to control pests in agriculture. According PEDIGO 1996, there are four main strategies to deal with insect pests:
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
reducing the carrying capacity so that the general equilibrium position2 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:
“useofvariousmethodstocombatpestsasopposedtoutilizinga single approach (chemicals)”[www.biotech.ca]
to a complex proposal:
“Asystemsapproachthatcombinesa 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 economically damaging levels”[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
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.
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
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.
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
1 cp.: Natural Resource Institute in: Thomas 1999, p. 5944
2 the pest’s long term average density
3 cp.: Pedigo 1996, p. 286ff
4 cp.: Oregon State University 2007, http://oregonstate.edu/~muirp/pesthist.htm
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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