Pests, Plagues & Politics
Lecture 15 Chemical Control
Pre- & Post DDT
Xenophon
Student of Socrates
“Crop protection
is in the hands of
the Gods.”
Key Points:
Chemical control
• Important ancient pesticides
• Botanical insecticides
• Underlying reason for development of
synthetic insecticides
• Advantages/Disadvantages of DDT
• Define Integrated Pest Management (IPM)
Pesticide(s)
• Include
–Insecticides
–Herbicides
–Fungicides
–Rodenticides
–et alia
Early/ancient Insecticides of Value
• Tobacco & other botanicals
• Soapsuds [renewed with Safer’s Soap]
• Fish & Whale oil
– known as DORMANT OIL
• Dusts
–
–
–
–
charcoal & soot
sulfur & ground tobacco
lime powder
Plaster of Paris (ground)
The Botanicals
•
•
•
•
Tobacco (nicotine)
Rotenone (So. American)
Hellebore (1787 - France)
Pyrethrum - the most famous!!!
– From a daisy
– native to the Caucasus Mts. of eastern
Europe
– 1st commercialized in Armenia in 1807
– 1st U.S. in 1885 - still viable today.
– Ragwort - alkaloids
http://en.wikipedia.org/wiki/Tobacco
The pyrethrum daisy
Chrysanthemum cinerarifolium
http://en.wikipedia.org/wiki/Pyrethrum
First Synthetic Insecticides (the inorganics)
• Bordeaux Mix (hydrated lime & copper
sulfate)
• Paris Green (copper acetoarsenite)
• The elementals
– Antimony - Arsenic - Mercury - Selenium
• Hydrocyanic gas (a fumigant in citrus - ca.
1880)
Synthetic Organic Insecticides
• World War II - major problem with insect
vectored disease
• *“Arbor” disease {ARthropod BORne)
– malaria, typhus, dengue fever, encephalitis
• Major effort to find effective insecticides
• USDA - evaluated DDT from the Swiss
Geigy Company.
DDT
• EUREKA!!! - with even minute doses it killed
every bug tested.
– Potentially the “Silver
Bullet”
• Chemical analysis showed it to be:
– *Dichloro-Diphenyl-Trichloroethane
– a chlorinated hydrocarbon (CH)
– first synthesized in 1874 by Othmar Zeilder in
Germany
• Between 1941 & 1976 over 4.5 million tons
produced (about 1.5 pound for every living
human on earth today)
DDT
• Pluses:
– wide spectrum of insecticidal action
– simple structure & easy (& cheap) to
manufacture
– prolonged stability & residual activity
– low mammalian toxicity
TIME MAG.
1947
"The great
expectations held
for DDT have been
realized. During
1946, exhaustive
scientific tests have
shown that, when
properly used, DDT
kills a host of
destructive insect
pests, and is a
benefactor of all
humanity."
http://www.whale.to/a/ddt.html
Lots of
options
http://www.tc.umn.edu/~allch001/1815/pestcide/sim/background.htm
DDT – so what happened?
• Went from an EFFECTIVE tool in
medical entomology to
• Overused & Abused tool in
agricultural entomology
Bio-magnification
Bio-accumulation
http://web.bryant.edu/~dlm1/sc372/readings/toxicol
ogy/toxicology.htm
Chlorinated Hydrocarbons (CHs)
• Success of DDT led to the development of
additional CHs:
– Lindane, Dieldrin, Chlordane, Methoxychlor,
Heptachlor
• Prime characteristic being
– Environmental Persistence
• CHs are lipophilic & were eventually
spread throughout “spaceship earth”
Organophosphates (OPs)
• Concurrent with the development of CH
insecticides was work on another group.
• The OPs
– extremely toxic in small doses (hot)
– high mammalian & avian toxicity
– less persistent in the environment
• Malathion, Parathion et alia
In 1932, German chemist Willy Lange and his graduate student, Gerde von Krueger, first described the cholinergic nervous system
effects of organophosphates, noting a choking sensation and a dimming of vision after exposure.
Problems with synthetics
• OVERUSE
– environmental buildup
• NON-SPECIFICITY
– toxic to many taxa, including non-target insects
– removal of beneficial insect complexes
• RESISTANCE DEVELOPMENT
– over time a given insecticide loses effectiveness
against the target pest insect
Insecticide Resistance
• 1945: E.H. Strickland writes:
– “Could the Widespread Use of DDT be a
Disaster?”
• 1946 - houseflies resistant to DDT (Sweden)
• 1967 - 224 cases of documented resistance
• 1992 - 500+ cases!!!
Things Have Changed
• ECONOMICS
– many fewer pesticides now (EPA restrictions
& cost of P-cide development)
• EVER GROWING ENVIRONMENTAL ETHIC
– in the field of economic entomology
– by the government (EPA, ODE)
• NEW GENERATIONS OF INSECTICIDES
– ENVIRONMENTALLY SAFER
– MORE TARGET SPECIFIC
– VERY COSTLY
4th Generation Insecticides
• Insect Growth Regulator ‘mimics’
– Hormones that interfere with an insect’s
growth & development
• GMO
– Bt corn, cotton, et alia
– Developing problems here with resistance
INTEGRATED PEST MANAGEMENT
IPM
• Commencing in the 1960ties
• The use of multiple techniques & strategies
to control pest insect populations below an
economic level
• Chemicals are still used, but in combination
with other methods in a broader
understanding of a pest insect’s life history
Key Points:
Chemical control
• Important ancient pesticides
• Botanical insecticides
• Underlying reason for development of
synthetic insecticides
• Advantages/Disadvantages of DDT
• Define Integrated Pest Management (IPM)