Chapter 16 – Pests and Pest Control

27/10/2010 01:07

1. Define pests. Why do we control them?

Pest is any organism that is noxious, destructive or troublesome. Agricultural pests are organisms that feed on ornamental plants or agricultural crops or animals. Bringing pests under control has three main purposes: to protect our food, to protect our health, and for convenience.


2. Discuss two basic philosophies of pest control. How effective are they?

Chemical treatment seeks a “magic bullet” that will eradicate or greatly lessen the numbers of the pest organism. Although it has had much success, this approach gives only short-term protection. Furthermore, the chemical often has side effects that are highly damaging to other organisms. Ecological control seeks to give long-lasting protection by developing control agents on the basis of knowledge of the pest's life cycle and of ecological relationships. Ecological control emphasizes the protection of people and domestic plants and animals from damage from pests, rather than eradication of the pest organism. Integrated pest management (IPM) incorporates both above mentioned methods. IPM is an approach to controlling pest populations by using all suitable methods – chemical and ecological – in a way that brings about long-term management of pest populations and also has minimal environmental impact. This method is suitable where pesticides are seen as undesirable because of health risks or if the cost of pesticides is prohibitive.


3. What were the apparent virtues of the synthetic organic pesticide DDT?

DDT was extremely toxic to insects and seemed non-toxic to humans and other mammals. It was very inexpensive to produce. It was effective against a multitude of insect pests. DDT was also persistent, hence provided lasting protection and eliminating both material and labour costs of repeated treatments.


4. What adverse environmental and human health effects can occur as a result of pesticide use?

Chronic effects on human health: pesticides might have chronic effects even at low levels of exposure, including cancer, dermatitis, neurological disorder, birth defects, and infertility. Long term exposure to pesticides can trigger Parkinson’s disease. Endocrine disruptors: Numbers of pesticides interfere with reproductive hormones; at very low levels a number of chemicals are able to mimic or disrupt the effects of estrogenic hormones (sexual hormones that are highly potent at low concentrations). Environmental effects: abnormal sexual development of alligators and other animals in the wild; drastic declines in populations of many species of birds that feed at the tops of food chain, because their eggs break in the nest before hatching; bioaccumulation and biomagnification.


5. Define bioaccumulation and biomagnification.

Bioaccumulation – process where products that are absorbed with food or water are trapped and held by the body’s lipids, while the water and water-soluble wastes are passed in the urine. Because synthetics (e.g. pesticides) are unnatural compounds (usually highly soluble in lipids), the body cannot fully metabolize them and has no mechanism to extract them. Accordingly, trace levels consumed over time gradually accumulate in the body and may produce toxic effects sooner or later. Biomagnification – each organism accumulates a concentration of contaminant in its body that is many times higher than that in its food. In effect, the next organism in the food chain now has more contaminated food and accumulates contaminant to yet higher level. Finally, due to this multiplying effect the concentration of a contaminant builds up through the food pyramid.


6. Why are nonpersistent pesticides not as environmentally sound as first thought?

They are persistent enough to “ride the food supply from farmer to consumer”. Many of the nonpersistent pesticides are far more toxic than DDT. For instance organophosphates are responsible for an estimated 70% of all pesticide poisonings. Nonpersistent pesticides may still have far-reaching environmental impacts. For example in Argentina in 1995 farmers used organophosphates to control grasshoppers in sunflower farms, this caused terrible decrease (5% in one year) in Swainson’s hawks populations. Desirable insects (e.g. pollinating bees) may be just as sensitive as pest insects to nonpersistant pesticides. Nonpersistent chemicals are just as likely to cause resurgences and secondary-pest outbreaks as are persistent pesticides, and pests become resistant to nonpersistent pesticides just as readily too.


7. Describe the four categories of natural or biological pest control. Cite examples of each and discuss their effectiveness.

Cultural control (1) is nonchemical alteration of one or more environmental factors in such a way that the pest finds the environment unsuitable or is unable to gain access to its target. E.g. eliminating the plants that act as attractants (e.g. roses) and growing those which act as repellents. Control by natural enemies (2): introduction of natural enemies to the field/crops to cut down pests. For instance, various caterpillars have been controlled by parasitic wasps. The problem with using natural enemies is finding organisms that provide control of the target species without attacking other, desirable species. Effective natural enemies are not always readily available. Genetic control (3): most genetic control strategies are designed to develop genetic traits in the host species that provide the same incapability – that is, resistance to attack by the pest. E.g. cultivation of potato that is resistant to blight. This method holds unpredictable consequences in terms of biodiversity: definite possibility of developing “super weeds” that are resistant to the herbicides or plant viruses, as resistance genes are shared. Insects are more likely to develop resistance to Bacillus thuringiensis (Bt) plants much more readily than they would to occasional spraying of the Bt insecticide directly. All these methods are not well suited in developing countries as they foster a dependence on a costly annual supply of seeds under current corporation practices. Natural chemical control (4) aim is to isolate, identify, synthesize, and the use an insect’s own hormones or pheromones to disrupt its life cycle. Natural chemicals are nontoxic and they are highly specific to the pest in question. The enormous potential of natural chemicals has been recognized for at least 30 years.


8. Define term economic thershold as it is related to pest control. What are cosmetic spraying and insurance spraying?

Economic thershold means that damage caused by pests should be considered significant only when the economic losses due to the damage considerably outweigh the cost of applying a pesticide. The objective of pest control should not be to eradicate a pest totally. All that is needed is to keep population levels below the economic thershold (see Figure 16-19 on page 429). Insurance spraying – the use of pesticides to prevent losses to pests. Use of pesticides by growers that believe his/her plantings might be at risk. Cosmetic spraying – the use of pesticides to control pests that harm only the item’s outward appearance. Cosmetic spraying accounts for a significant fraction of pesticide use, does nothing to enhance crops yield or nutritional value, and results in an increase in pesticide residues remaining on the produce.


9. What are the four steps in IPM? Explain how IPM worked in Indonesia.

Integrated Pest Management aims to minimize the use of synthetic organic pesticides without jeopardizing crops: (1) Set action thresholds, identification of a point at which pests populations or environmental conditions indicate that some control action is needed; (2) Monitor and identify pests, trained staff (field scouts) identifies and monitors if pests populations exceeds the economic threshold; (3) Prevention, cultural and biological practices from the core of IPM; (4) Control, if pest control is still required in spite the preventive methods, here pesticides may be used, but quantities and brands that damage natural environment least. In Indonesia intensive use of pesticides were replaced by IPM by educating farmers who later on spread the knowledge in entire local municipality. Instead of heavy pesticide praying light spraying is used to preserve pests’ natural enemies. Introduction of IPM helped Indonesian government to save millions of dollars annually from pesticides and spraying equipment.


10. What is organic food, and how is it now certified?

Organically grown food is grown by employing traditional farming methods with diverse crops. According to USDA no product involving genetically engineered or irradiate foods or food fertilized with sewage sludge can be certified as 100% organic. The standards also prohibit the use of conventional pesticides, antibiotics, growth hormones, and chemical fertilizers. To market certified organic foods, farmers now must have their operations scrutinized by USDA-approved inspectors.


11. How does FIFRA attempt to control pesticides? What new perspectives does FQPA bring to the policy scene?

FIFRA requires manufacturers to register their pesticides with the EPA before marketing them. The registration includes testing toxicity to animals (and, by extrapolation, to humans). From the tests usage standards are set. FQPA established act where following requirements are listed:

-          The new safety standard is “a reasonable certainty of no harm” of substances applied to foods.

-          Special consideration must be given to the exposure of young children to pesticide residues.

-          Pesticides and other chemicals are prohibited if, when consumed at average levels over the course of a lifetime.

-          All possible sources of exposure to a given pesticide must be evaluated, not just exposure from food.

-          All older products on the market before 1996 must be reassessed according to the new requirements.

-          The same standards are to be applied to raw and processed food.


12. Discuss recent policy regarding the export of pesticides to developing countries.

The U.S. currently exports more than 200 000 tons of pesticides each year. Some 25% of this total consists of products banned in U.S. itself. However there is now a process of prior informed consent (PIC), whereby exporting countries inform all potential importing countries of actions they have taken to ban or restrict the use of pesticides or other toxic chemicals. In addition an international Code of Conduct on the Distribution and Use of Pesticides (2002) has also improved the situation on market by stating in detail the conditions of safe pesticide use. On the other hand this act (Code of Conduct) is voluntary and not legally binding. Nevertheless, there has been a great progress in addressing this difficult problem in developing countries.