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