Transcript plant-derived insecticides

PLANT-DERIVED INSECTICIDES
Nicotine
• Source:
– Nicotiana tabacum, Nicotiana rusticum
• Characteristics
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Colorless liquid
Oxidizes to brown
Hygroscopic
Water miscible below 60o
Soluble in many organic solvents
Nicotine
• Source:
– Nicotiana tabacum,
Nicotiana rusticum
• Characteristics
– Colorless liquid
– Oxidizes to brown
– Hygroscopic
– Water miscible below 60o
– Soluble in many organic
solvents
Nicotine
• Mechanism
– Mimics acetylcholine at nerve
synapse
• Stomach and contact poison
• Site of action:
• Formulations
– CNS
– Sprays: 0.05-0.1%
– Autonomic nerves
• Easier form to manage
– Some voluntary peripheral nerves
– Dusts:1-2%
• LD50
• Irritant
– Rats, po: 50 mg/kg
• More likely to cause applicator
– Rabbits, dermal: 50 mg/kg
exposure
• Symptoms
• Minor use insecticide since
– Vomiting, tremors, convulsions,
synthetics were developed
altered blood pressure
– Death from block at respiratory
neuromuscular junctions
• Uses:
– Against sucking insects
LD50 = 450 mg/kg
Sabadilla
• Sabadilla CAS # = 802-85-77
• Source:
• Seeds of Schoenocaulum officinale
– Member of lily family
• Toxin not present in other plant parts
• Active ingredients are alkaloids
– Veratrine and cevadine thought to be primary toxicants
– cevine, cevacine, and sabadine
– Other alkaloids also present and contribute to toxicity
• Characteristics
– Poor selectivity
– Generally used as ground up seeds
– Toxic to honey bees
Sabadilla
Sabadilla
• Internally
– Anthelmintic (obsolete)
• Externally
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– Against lice? (Also obsolete?)
Gardening
– 5-20% dust or spray
– Contact and stomach poison
– Labeled for use on
vegetables
– Controls
• caterpillars, leafhoppers,
thrips, stink bugs, squash
bugs.
• Toxicology
– Veratrine and cevadine may be
critical toxicants
– Mechanism
• Affect voltage-dependent Na
channels
– Delays channel shutting
– Increases probability of
channel opening
– Direct effect on muscle
contraction
– Heart stops in systole as
contractions become fewer
and longer
– LD50 of sabadilla
• Rats, po: 4,000-5,000 mg/kg
• Blackbirds, po: 18 mg/kg
Rotenone
• Source
– Various tropical legumes, including
• Derris elliptica, D. malaccensis (Malaysia)
• Lonchocarpus utilis, L. urucu (South America)
• 5 active ingredients known
– Rotenone most effective
» 5-10x activity of other compound
Uses
• Labeled for
– Vegetables, berries, tree fruits, nuts, forage crops, sugar cane
– Dusts, wettable powders, sprays
• Usually < 5%
• Original use included fishing
• Is used to control undesirable fish in managed waters
• Active 1-2 days on plants
Toxicology
• Mechanisms
– Inhibits NADH ---> NAD by cytochrome b
– Same in insects and mammals
– Efficiently metabolized by mammalian liver
• LD50
– Rats
• po: 60-130 mg/kg
• ip: 1-2 mg/kg
– Other effects
• Contact dermatitis
• Chronic effects
– Fetotoxicity at maternally lethal doses
– Carcinogenic?
• Delays progression of cells through cell cycle
– Mechanism uncertain
Ryanodine
• Source
– Powdered stem of Ryania
speciosa
– Water-soluble extract
contains several
structurally related
ryanoids
• Uses
– Apple and citrus
– Voluntary cancellation
by manufacturers in
1990s
– Sales did not warrant
carrying out required
toxicity studies
Toxicology
• Mechanism
– At µM levels, irreversibly activates Ca++ channel in sarcoplasmic
reticulum of muscle
• Floods muscle cell with Ca++ ions
• Induces sustained contraction of skeletal muscles
• Paralysis results
– Ryanodine receptor
• Calcium channels in muscle, other excitable aimal tissue
• Several subtypes
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RyR1 in skeletal muscles
RyR2 in heart muscle
RyR3 - wide distribution; also in brain
RyR4: only in fish
• Major mediator of Ca-induced Ca-release
• LD50 po, rats: 750-1250 mg/kg
Strychnine
• Source
– Strychnos bux vomica tree
• seeds
• Mechanism
– Antagonizes strychninesensitive glycine receptor
• ligand-gated chloride
channel in CNS
• Uses
– Against vertebrtates
• LD50 1 mg/kg po
• Current Regulatory Status
– ????