Transcript Slide 1
Chapter 23 The Pesticide Dilemma
Defining Pests
o o o Organism that is oxious, destructive Competes with us for food, invades lawns/gardens, destroys houses, spreads disease Injurious plant or animal
Defining Pests
o Typical Characteristics: • • • • • Reproduce rapidly Migrate quickly Pioneers in ecological succession Compete aggressively against more specialized species Generalists
Defining Pests
o Categories: • • • • • • Agricultural pests: feed on crops or ornamental plants Arachnids: spiders, ticks, flour/grain/cheese mites Crustaceans: woodlice/pill bugs, flour/grain/cheese mites Pathogens: bacteria, viruses, fungi Rodents: house mouse, common rat Insect pest examples: ……
o
Types of Pesticides
Pesticides: (Biocides) Chemicals developed to kill organisms that we consider undesirable. • 1. Insecticides - Insect-killers • 2. Herbicides - Weed-killers • 3. Fungicides – Fungus-killers • 4. Nematocides – Roundworm-killers • 5. Rodenticides – Rat- and Mouse-killers
Pesticide Types
o First-generation pesticides: • • • • • Sulfur – used as an insecticide since 500 BC Arsenic (As), lead (Pb) and mercury (Hg) by the 1400’s Nicotine sulfate – extracted from tobacco leaves in the 1600s Pyrethrum – obtained from the heads of chrysanthemum flowers Rotenone – from the root of the derris plant ***Resistant pest populations developed
Types of Pesticides
o Second-generation: o Since 1950 pesticide usage has increased 50 fold and toxicities have increased 10 fold. o • 10X more synthetic pesticides are used on the average home than on croplands in the US. o • ~75% of synthetic pesticides are used in the developed countries
Types of Pesticides
o o worldwide. In the United States, about 630 different biologically active (pest-killing) ingredients and 1,820 inert (inactive) products. • DDT – 1939, Entomologist Paul Mueller discovered that DDT (dichlorodiphenyltrichloroethane) was a potent insecticide. It soon became the world’s most-used pesticide. Awarded a Nobel Prize in 1948. • Broad-spectrum agents – toxic to many species • Selective-spectrum agents – effective against a narrowly defined group of organisms.
Types of Pesticides
Types of Pesticides
o 1. Persistence – the length of time in which pesticides remain deadly in the environment; this may vary from days to years. o 2. Biomagnification – the process by which toxins accumulate the higher you go in the food chain (generally because the toxin is not water soluble and therefore not easily excreted).
Pesticide Types – Chemical Structure
o Inorganic pesticides (e.g. arsenic, copper, lead and mercury) • Generally highly toxic • Remain in soil forever • Generally neurotoxins
Types of Pesticides
o Natural organic pesticides (botanicals) • Extracted from plants • Nicotine: toxic to a broad spectrum of organisms • Rotenone: used to kill fish • Turpentine and phenols: effective pesticides
Types of Pesticides
o Fumigants (e.g. carbon tetrachloride, carbon disulfide) • • Generally small molecules Gasify easily • • Penetrate rapidly into a variety of materials Used to sterilize soil • • Prevent decay or rodent and insect infestations of stored grain • Very dangerous to workers who apply them Use has been curtailed or banned altogether
Types of Pesticides
- Chlorinated Hydrocarbons (organochlorines) (e.g. DDT, chlordane, aldrin) • Inhibit nerve membrane ion transport and block nerve signal transmission • Fast acting and highly toxic in sensitive organisms • Highly persistent in soil • Stored in fatty tissues of a variety of organisms • Become concentrated through food chains
Types of Pesticides
o Organophosphates (e.g. parathion, malathion) • Inhibit cholinesterase which is an enzyme essential for removing excess neurotransmitter from synapses in peripheral nervous system • Extremely toxic to mammals, birds, and fish • Less persistent in environment than organochlorines
Types of Pesticides
o Carbamates (e.g. carbaryl, aldicarb) • Share many organophosphate properties • Extremely toxic to bees
Types of Pesticides
o Microbial agents and biological controls • Living organisms or toxins derived from them used in place of pesticides • Some species of bacteria kill caterpillars or beetles by releasing a toxin that ruptures that digestive tract. • Some parasitic wasps attack moth and caterpillar eggs
Benefits of Pesticides
o Benefit: Disease control • Fleas, lice and mosquitoes carry disease • Malaria- mosquito born • • • 2.7 million people die each year Few drugs available, so focus is on killing mosquitoes DDT
o
Benefits of Pesticides
Disease Control
• • • Diseases spread by biting insects • o Malaria • o Yellow fever • o Encephalitis • o Sleeping sickness Diseases can be reduced by judicious use of pesticides.
Benefits
o
Crop Protection
• Plant diseases, insect and bird predation, and competition by weeds reduce crop yields worldwide by at least 1/3. • Without modern chemical pesticides, losses might be much higher. • Farmers may save $3 to $5 for every $1 spent on pesticides. o Lower costs and generally better quality for consumers • Cosmetic damage can greatly reduce the economic value of crops
Pesticide Problems
o
Effects on Nontarget Species
• Estimated that up to 90% of the pesticides we use never reach their intended targets. • o Sometimes effects are immediate • A 1999 study linked insecticide (4-nonylphenol) spraying on Canadian forests with dramatic declines in Atlantic salmon
Pesticide Problems
o
Pesticide Resistance and Pest Resurgence
• Pesticides almost never kill 100% of a target species even under the most ideal conditions • The most resistant members of a population survive pesticide genes that enable them to withstand further chemical treatment. • Pest resurgence: because most pests propagate rapidly and produce many offspring, the population will quickly rebound with pesticide resistant individuals. •
Pesticide Problems
o
Creation of New Pests
• Broadcast pesticide spraying may kill beneficial predators that previously kept a number of pests under control • Higher trophic levels are more likely to be knocked out than lower ones.
Pesticide Problems
o
Persistence and Mobility in the Environment
• The qualities that make DDT and other chlorinated hydrocarbons so effective (stability, high solubility, and high toxicity), also make them environmental nightmares. • o Some of the compounds have been discovered far from any possible source and long after they were used. • o Can accumulate in polar regions through a series of evaporation, condensation, and precipitation events. • o Have a high affinity for fat
Pesticide Problems
o Breakdown by-products may still be present in the environment. • In a 1999 study, breakdown by-product of DDT, p,p'-DDE , is found in the amniotic fluid of 30% of a sample of pregnant women in Los Angeles, CA. o o Atrazine and alochlor are widely used herbicides • 30% of all community wells and as much as 60% of all private wells in the mid-western corn belt are contaminated with atrazine and alochlor. o o Because of the ubiquity of these persistent organic pollutants (POPs), there is a widespread movement to ban them.
Human Health Problems
o Pesticide effects on human health can be divided into 2 categories • Short-term effects, including acute poisoning and illnesses caused by relatively high doses and accidental exposures. • Long-term effects suspected to include cancer, birth defects, and immunological problems, and other chronic degenerative diseases.
Health Problems
o The World Health Organization (WHO) estimates that between 2.5 and 5million people suffer from acute pesticide poisoning. • o At least 2/3 of this illness and death results from occupational exposures in developing countries o • • o Children from farming communities where pesticide use is high had diminished growth and development as compared to children with
Alternatives
o In many cases, improved management programs can cut pesticide use between 50 and 90% with reducing crop production or creating new diseases
Alternatives
Behavioral: o Crop rotation (growing a different crop in a field each year in a 2-to6-year cycle) keeps pest populations from increasing. o • Mechanical cultivation can substitute for herbicide treatment, but can increase erosion o • Flooding fields before planting can suppress both weeds and insect pests. o • Burning crop residues and replanting with cover crop can suppress weeds and insect pests.
Alternatives
Behavioral: • Habitat diversification • Growing crops where pests are absent • Adjusting planting times can avoid pest outbreaks • Switching from monoculture to mixed polyculture • Tillage at certain times
Alternatives
o Biological: predators or pathogens that can control many pests more cheaply and safely than broad-spectrum, synthetic chemicals • o Bacteria can be sprayed on crops to control pests. • o Ducks, chickens, and gees can rid fields of both insects and weeds. • o Insects including mantises and ladybugs protect against a multitude of pests.
Alternatives
o Biological • • • Plants with insect-repelling properties such as garlic and marigolds. Herbivorous insects can be used to control weeds. Genetics and bioengineering • Breeding livestock that tolerate pests well •
Integrated Pest Management
o • Integrated pest management (IPM): flexible, ecologically based pest-control strategy that uses a combination of techniques applied at specific times, aimed at specific crops and pests. • Does not give up pest controls entirely. • Enhances growth and diversity of beneficial organisms. • Enhance plant defenses
Systems Approach- Integrated Pest Management (IPM)
o o IPM • Combination of pest control methods that keeps pest population low without economic loss Conventional pesticides are used sparingly when other methods fail
Systems Approach- Integrated Pest Management (IPM)
o Rice Production in Indonesia
IPM Introduced
Benefits and Problems with Pesticides
o Problem: Mobility in the Environment • • Do not stay where they are applied Move through soil, water and air
Risk of Pesticides to Human Health
o Short-term Effects of Pesticides • • • Handling food with pesticide residue Mild case: nausea, vomiting, headaches Severe case: damage to nervous system,
Risk of Pesticides to Human Health
o Long-term Effects of Pesticides • • • • Cancer- lymphoma Breast cancer Sterility Miscarriage • • • Birth defects Decreases body’s ability to fight infection Potential connection to Parkinson’s disease
Alternatives to Pesticides
o Irradiating Food • • • Harvested food is expose to ionizing radiation, which kills many microorganisms Predominantly used on meats Somewhat controversial due to potential for free radicals
Laws Controlling Pesticide Use
o o o o o Food, Drug, and Cosmetics Act (1938) Pesticide Chemicals Amendment (1954) Delaney Cause (1958) Federal Insecticide, Fungicide, and Rodenticide Act (1947) Food Quality Protection Act (1996)
Manufacture and Use of Banned Pesticides
o o o Some US companies still make banned or seriously restricted pesticides • Product is exported May lead to the importation of food tainted with banned pesticides Global ban of persistent organic pollutants • Stockholm Convention on Persistent Organic Pollutants (2004)