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Pyrethroids

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Currently make up 20% of the total volume of insecticides used all over the world ... States reaches 1000 tons per year, kerosine extracts replace powder in home use ... – PowerPoint PPT presentation

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Title: Pyrethroids


1
Pyrethroids
Melissa Hardstone mch38_at_cornell.edu March 10, 2008
2
Why do we care?
  • Currently make up 20 of the total volume of
    insecticides used all over the world
  • Low mammalian toxicity
  • 2 class of insecticide used today (OPs are 1)

3
Discovery and history
  • Early 1800s housewives in Persia would keep
    dried flowers around to kill insects (cultivation
    starts in 1840)
  • 1860 - pyrethrum powder exported to the United
    States
  • 1914 - due to World War I, the cultivation of
    pyrethrum is suspended in Persia, with Japan
    slowly taking over the market
  • 1919 - pyrethrum import in the United States
    reaches 1000 tons per year, kerosine extracts
    replace powder in home use

4
  • 1924 - identification of the active substances
    structure from pyrethrum extract
  • 1928 - the use of pyrethrum powder almost ceases
  • 1945 - Kenya is the world's main pyrethrum
    producer (and still is)
  • 1972 - world pyrethrum production amounted to
    more than 21,000 tons (with production in Kenya,
    Tanzania, Rwanda, Ecuador and Japan)

5
Botanical Chrysanthemum cinerariaefolium
  • Flowers are harvested by hand, dried, and
    extracted
  • Extracted product contains 1-3 pyrethrins by
    dry weight (3-4 mg pyrethrins/flower)
  • Casida (1980) Envir. Health Persp.
  • Remainder of product is made of waxes and
    pigments
  • Pyrethrins are especially good for knockdown of
    insects

6
Development/Manufacturing
  • 1960s Dr. Casida in Berkeley
  • Identified major pathways of breakdown of
    pyrethrins and early pyrethroids
  • 1960s and 1970s Era of synthesis
  • Pyrethroids take 2nd place as most widely used
    class, beating out carbamates
  • 1980-1997 Commercial development begins
  • Dr. Elliott _at_ Rothamsted, Sumitomo, Roussel UCLAF

7
Whats in the crude extract
68
22
10
Katsuda (1999) Pesticide Science
8
Type 1 versus Type 2
  • Type 1
  • Better knockdown
  • Type 2
  • Better kill

Casida (1980) Environ. Health Persp.
9
Properties
  • No strict parent structure
  • Properties vary within the class
  • Toxicity varies with conformational structure
  • Generally
  • Broad spectrum - selectivity between pest and
    nat. enemy
  • Toxic to fish, but otherwise not too bad in
    nature - plankton
  • Dermal irritation
  • Insecticidal properties trans 2x gt cis

Acid moiety
Ester linkage
Alcohol moiety
10
Toxicity of isomers
  • Varies depending on conformation
  • Example Cinerin I isomers to housefly

11
Examples(based on modified acid moeity)
Katsuda (1999) Pesticide Science
12
  • Permethrin

How many isomers?
  • Broad spectrum
  • Raid, Dragnet, Ambush
  • First marketed in 1977
  • Rat oral LD50 4000 mg/kg
  • House fly topical LD50 1.1 ug/g

13
  • Cypermethrin

How many isomers?
  • Broad spectrum
  • Ammo, Cymbush, Cynoff, Demon
  • Rat oral LD50 250 mg/kg
  • House fly topical LD50 0.35 ug/g

14
  • Deltamethrin

(R)
(R)
  • All activity due to single isomer 1-R cis or
    trans, a-S
  • Broad spectrum
  • Used worldwide, but not in US
  • Rat oral LD50 135-5000 mg/kg
  • House fly topical LD50 0.1 ug/g

15
  • Fenvalerate
  • Broad spectrum
  • Pyrdrin, Sumicidin
  • Rat oral LD50 450 mg/kg
  • House fly topical LD50 4.2 ug/g

16
Examples (based on modified alcohol moiety)
Katsuda (1999) Pesticide Science
17
Allethrin
  • 1st synthetic pyrethroid - 1948
  • trans isomer most toxic (often 41 transcis
    mixture)
  • 1R-trans 4(RS)(l-allethrolone d-trans acid)
    bioallethrin
  • 1R-trans 4S (S) bioallethrin
  • Rat oral LD50 1110 mg/kg

How many isomers?
23 8
18
Phenothrin
  • Sumithrin, Anvil, Duet
  • Fleas, ticks, head lice - use cancelled in 2005
  • Adverse side effects hair loss, death of animals

19
Other examples
20
  • Bifenthrin
  • Cotton and greenhouse ornamentals - acaricide
  • Capture, Ortho Home Defense Max, Talstar
  • Rat oral LD50 55 mg/kg
  • House fly topical LD50 1.4 ug/g

21
  • Tefluthrin
  • Soil insecticide
  • Force
  • Rat oral LD50 20-35 mg/kg

22
  • Esfenvalerate
  • S, S isomer
  • Asana
  • Rat oral LD50 75-460 mg/kg

23
Pyrethroid-like compound examples
Claims that pyrethroids are highly toxicity to
fish, so not used in water systems. True in the
lab, but not nature because plankton metabolize
the compounds. Some alternatives sought out.
24
  • Etofenprox

Notice anything about the structure?
  • Broad spectrum
  • Not registered in the US
  • Trebon
  • Rat oral LD50 gt42000 mg/kg
  • House fly topical LD50 0.4 ug/g

25
Silafluofen
  • High insecticidal activity
  • Low mammalian/fish toxicity
  • LD50 trout gt1000 mg/L (permethrin 0.0025 mg/L)
  • High chemical stability
  • Contact/stomach poison

Katsuda (1999) Pesticide Science
26
Useful nomenclature
  • Pyrethrum dried flowers/plant
  • Pyrethrum extract
  • How many compounds in the extract?
  • Pyrethrins purified isomers from crude extract
  • Pyrethroids synthetic analogs of pyrethrins
  • Early pyrethroids those made from 1948-1964
  • Agricultural pyrethroids used in the field

27
Next time
  • Poisoning symptoms
  • Mode of action
  • Metabolism
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