Chapter 23The Pesticide Dilemma
Pests
Pest – any organism that interferes in some way with human welfare or activities
grouped by target organism they attack Insecticides – kills insects Herbicides – kills plants Fungicides – kills fungus Rodenticides – kills rodents
Agriculture
Sector that uses the most pesticides (85% world wide)
Narrow spectrum pesticides – pesticides that kill only the organism for which it was intended.
Broad spectrum pesticides – pesticides that kill a wide variety of organisms.
Additional problems with pesticides – more in environment, don’t degrade.
What is a Pesticide Broad spectrum pesticide
A pesticide that kills a variety of organisms, not just the targeted organisms
First generation pesticide Inorganic compounds
Lead, mercury and arsenic
Organic compounds (Botanicals- plant derived pesticides) Nicotine and pyrethrin
What is a Pesticide
Second generation pesticide Synthetic poison Ex: DDT
Major Groups of Insecticides
Chlorinated Hydrocarbons Organic compound containing Chlorine Ex: DDT Slow to degrade and persist in the environment Banned or largely restricted Endosulfan, lindane & methoxychlor still in use
Organophosphates Organic compounds that contain phosphorus Most poisonous insecticide Very poisonous & toxic to birds, bees and aquatic
organisms Do not persist as long as chlorinated hydrocarbons
Cabamates Derived from cabamic acid, not toxic to mammals, broad
spectrum
Major Kinds of Herbicides Selective Herbicides
Kill only certain types of plants Can be classified to the type of plant they kill
Broad-leaf herbicides-which kill broad-leaf plants but not grasses
Grass herbicides-kill grasses but not other plants
Ex: 2,4-D Non selective herbicides-kills all vegetation Famous example – Agent Orange: mixture of two
herbicides that contain dioxins
includes a variety of health effects: tissue cancer, skin diseases, urological disorders & birth defects
Benefits and Problems with Pesticides Benefit: Disease control, crop protection
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
Benefits and Problems with Pesticides
Benefit: Crop Protection Pests eat and destroy
1/3 of world’s crops Farmers save $3 to $5
for every $1 they invest in pesticides
Problem: Evolution of Genetic Resistance Pest populations are
evolving resistance to pesticides (right)
“Pesticide Treadmill” Cost of applying pesticide increases
Because they must be applied more frequently or in larger doses
While their effectiveness decreases Because of increased genetic resistance in pests
Resistance Management Strategies for managing genetic resistance in order to
maximize the period in which a pesticide is useful Delays the evolution of genetic resistance
Refuge of untreated plants-leave some population untouched to prevent resistance
Pesticide Resistance
Benefits and Problems with Pesticides
Problem: Imbalances the Ecosystem Spraying to kill insects can affect birds,
rabbits, etc. Despite 33-fold increase in pesticides since
the 1940s, crop loss has not really changed
Benefits and Problems with Pesticides Problem: Creation of New Pests
Infestation of red scale insects on lemons after DDT sprayed to control another pest
Benefits and Problems with Pesticides Problem: Persistence, Bioaccumulation, and
Biological Magnification Bioaccumulation
The buildup of a persistent pesticide or other toxic substance in an organisms body
Biological magnification Increased
concentration of toxic chemicals in tissues of organisms at higher trophic levels
Ex: Peregrine falcons (right)
Benefits and Problems with Pesticides Problem: Mobility in the Environment
Do not stay where they are applied Move through soil, water and air
Risk of Pesticides to Human Health
Short-term Effects of Pesticides Handling food with pesticide residue
Mild case: nausea, vomiting, headaches
Severe case: damage to nervous system
Lead-neurological development
Mercury-biomagnification via
fish and crabs
Risk of Pesticides to Human Health
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 Using cultivation methods to control pests
Interplant mixtures of plants (alternating rows) Strip cutting-leaving strips of un-harvested crops Proper timing of planting, fertilizing, and irrigating Crop rotation
Biological Control Use of naturally occurring disease organisms,
parasites or predators to control pests (such as lady bugs and praying mantises)
Must take care that introduced agent does not attack unintended hosts
Alternatives to Pesticides Pheromones and Hormones
Can use pheromones to lure pests to traps By applying insect hormones at wrong time in life cycle, insects
can be killed off Reproductive Controls
Sterilizing some of the members Sterile male technique
Genetic Controls Genetically Modified plants (GMOs)
Bt toxin Potential problem: may affect non-target species (monarch butterfly)
Quarantine Restriction of the importation of exotic plant and animal material
that might harbor pests Effective, but not foolproof
Systems Approach- Integrated Pest Management (IPM)
IPM Combination of pest control
methods that keeps pest population low without economic loss
Conventional pesticides are used sparingly when other methods fail
IPM uses 3 premises1. Management rather than eradication2. Economic injury-don’t take action until
this point, use non toxic first3. Education-educate farmers as to all
the alternativesScout and spray-monitor for pests & only
spray when they become a problemCalendar Spraying-regular spraying
whether need or not
Rice Production in Indonesia
Systems Approach- Integrated Pest Management (IPM)
IPM Introduce
d
Alternatives to Pesticides
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 Food, Drug, and Cosmetics Act (1938) recognized need to regulate pesticides but had no teeth Pesticide Chemicals Amendment (1954) established acceptable levels of pesticides in food Delaney Cause (1958) prohibits cancer-causing substances in food (applies only to
pesticides) Federal Insecticide, Fungicide, and Rodenticide Act
(1947) regulated pesticide sale to prevent the sale of lemon (pesticides that
don’t work) requires disclosure of active ingredients but not inert ingredients Food Quality Protection Act (1996) Established pesticide residue limits in both raw and processed foods
Manufacture and Use of Banned Pesticides
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) Stockpiles of banned pesticides, predominantly in
developing countries
Manufacture and Use of Banned Pesticides
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