PLANT-DERIVED INSECTICIDES

Nicotine

• Source:– Nicotiana tabacum, Nicotiana rusticum

• Characteristics– 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

• Uses:– Against sucking insects

• Stomach and contact poison• Formulations

– Sprays: 0.05-0.1%• Easier form to manage

– Dusts:1-2%• Irritant• More likely to cause applicator

exposure• Minor use insecticide since

synthetics were developed

• Mechanism– Mimics acetylcholine at nerve

synapse• Site of action:

– CNS– Autonomic nerves– Some voluntary peripheral nerves

• LD50 – Rats, po: 50 mg/kg– Rabbits, dermal: 50 mg/kg

• Symptoms– Vomiting, tremors, convulsions,

altered blood pressure– Death from block at respiratory

neuromuscular junctions

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– 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

– 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 strychnine-sensitive glycine receptor

• ligand-gated chloride channel in CNS

• Uses– Against vertebrtates

• LD50 1 mg/kg po

• Current Regulatory Status– ????