PLANT-DERIVED INSECTICIDES

Nicotine Source: –Nicotiana tabacum, Nicotiana rusticum Characteristics –Colorless liquid –Oxidizes to brown –Hygroscopic –Water miscible below 60 o –Soluble in many organic solvents

Nicotine Source: –Nicotiana tabacum, Nicotiana rusticum Characteristics –Colorless liquid –Oxidizes to brown –Hygroscopic –Water miscible below 60 o –Soluble in many organic solvents

Nicotine Uses: –Against sucking insects Stomach and contact poison Formulations –Sprays: % 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 LD 50 –Rats, po: 50 mg/kg –Rabbits, dermal: 50 mg/kg Symptoms –Vomiting, tremors, convulsions, altered blood pressure –Death from block at respiratory neuromuscular junctions

LD 50 = 450 mg/kg

Sabadilla Sabadilla CAS # = 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

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 –LD 50 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 LD 50 –Rats po: 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 LD 50 po, rats: mg/kg

Strychnine Source –Strychnos bux vomica tree seeds Mechanism –Antagonizes strychnine- sensitive glycine receptor ligand-gated chloride channel in CNS Uses –Against vertebrtates LD 50 1 mg/kg po Current Regulatory Status –????