Pests, Plagues & PoliticsPests, Plagues & PoliticsLecture 15 Chemical ControlLecture 15 Chemical Control

Pre- & Post DDTPre- & Post DDT

XenophonXenophon

Student of SocratesStudent of Socrates

“Crop protectionis in the hands ofthe 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 ValueEarly/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 BotanicalsThe 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 daisyThe pyrethrum daisyChrysanthemum cinerarifoliumChrysanthemum cinerarifolium

http://en.wikipedia.org/wiki/Pyrethrum

First Synthetic Insecticides (the inorganics)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 InsecticidesSynthetic 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.

DDTDDT

•EUREKA!!! - with even minute doses it killed every bug tested.– Potentially the “Silver BulletSilver Bullet”

• Chemical analysis showed it to be:– *D*Dichloro-DDiphenyl-TTrichloroethane– 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)

DDTDDT

• PlusesPluses:– wide spectrum of insecticidal action– simple structure & easy (& cheap) to

manufacture– prolonged stability & residual activity– low mammalian toxicity

"The great "The great expectations held expectations held for DDT have been for DDT have been realized. During realized. During 1946, exhaustive 1946, exhaustive scientific tests have scientific tests have shown that, when shown that, when properly used, DDT properly used, DDT kills a host of kills a host of destructive insect destructive insect pests, and is a pests, and is a benefactor of all benefactor of all humanity."humanity."

TIME MAG.TIME MAG.19471947

http://www.whale.to/a/ddt.html

Lots of Lots of optionsoptions

http://www.tc.umn.edu/~allch001/1815/pestcide/sim/background.htm

DDT – so what happened?DDT – so what happened?

• Went from an Went from an EFFECTIVEEFFECTIVE tool in tool in medical entomology tomedical entomology to

•OverusedOverused & & AbusedAbused tool in tool in agricultural entomologyagricultural entomology

Bio-magnificationBio-magnification

Bio-accumulationBio-accumulation

http://web.bryant.edu/~dlm1/sc372/readings/toxicology/toxicology.htm

Chlorinated Hydrocarbons (CHs)Chlorinated Hydrocarbons (CHs)

• Success of DDTDDT 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)Organophosphates (OPs)

• Concurrent with the development of CH insecticides was work on another group.

• The OPsOPs

– 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 syntheticsProblems with synthetics

• OVERUSEOVERUSE– environmental buildup

• NON-SPECIFICITYNON-SPECIFICITY– toxic to many taxa, including non-target insects

– removal of beneficial insect complexes

• RESISTANCE DEVELOPMENTRESISTANCE DEVELOPMENT– over time a given insecticide loses effectiveness

against the target pest insect

Insecticide ResistanceInsecticide 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 ChangedThings Have Changed

• ECONOMICSECONOMICS– many fewer pesticides now (EPA restrictions

& cost of P-cide development)• EVER GROWING ENVIRONMENTAL ETHICEVER GROWING ENVIRONMENTAL ETHIC

– in the field of economic entomology– by the government (EPA, ODE)

• NEW GENERATIONS OF INSECTICIDESNEW 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 MANAGEMENTINTEGRATED PEST MANAGEMENT

IPMIPM• 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)