S2 L2 Insecticides - natural

Anna Drew

with slide contribution from Martin Wilks, Syngenta,& Rhonda Hamm

Insecticide history• Inorganics – arsenic, sulphur• Botanicals – pyrethrum• Petroleum oils – horticultural/summer/foliar oils• Organochlorines (DDT, cyclodienes)• Organophosphates (Class 1)• Insect growth regulators• Pyrethroids (Class 2)• Microbial toxins (Bt)• Pheromones

Importance of Pesticide Regulation

PESTICIDE REGULATION is designed to protect the health of those who apply pesticides, those who are exposed as bystanders, and those who are exposed to residues in food and water.

Stages of Risk Assessment

Toxicological Hazard Assessment

Identification of intrinsic toxicological properties and assessment of their relevance to humans

World Health Organization (WHO) Classification of Pesticides by Hazard

LD 50 for the rat (mg/kg body weight)

Class Oral Dermal

Solids Liquids Solids Liquids

Ia Extremelyhazardous 5 or less 20 or less 10 or less 40 or less

Ib Highlyhazardous 5 - 50 20 - 200 10 - 100 40 - 400

hazardous 50 - 500 200 - 2000 100 - 1000 400 - 4000

III Slightlyhazardous Over 500 Over 2000 Over 1000 Over 4000

II Moderately

Key Toxicological Studies Used in Risk Assessment for Pesticide

Operators

• 90 day, sub-acute oral dosing study

• 21/28 day dermal dosing study

• Reproductive toxicity studies

• 1 year oral dosing study (depending on use pattern)

Stages of Risk Assessment

Toxicological Hazard Assessment

Dose-ResponseEvaluation

Determination of quantitative relationships between internal dose and effects for the endpoints of concern

                                                                                        

The Dose Response Curve

Stages of Risk Assessment

Toxicological Hazard Assessment

Human ExposureAssessment

Dose-ResponseEvaluation

Assessment of intensity, frequency, duration and routes of human exposure for the purpose of quanti-fication of internal dose

Stages of Risk Assessment

Toxicological Hazard Assessment

Human ExposureAssessment

Risk Characterisation

Dose-ResponseEvaluation

Integration of available information to produce conclusions on the probability of adverse effects

Early

Late

• Physico-chemical properties• Acute oral toxicity, mutagenicity• Dermal absorption, inhalation

toxicity• Subacute & subchronic toxicity• Reproductive & developmental

toxicity• Chronic toxicity, carcinogenicity

Toxicology Information in the Development Process

Evolution of Crop Protection Product Formulations

Soluble and stable in water

Solid or unstable in water

Soluble in organic solvent

1960 1970 1980 1990 2000

Soluble Liquid

Wettable PowderWettable Powder

WP in WSB

WG

SCSC (suitable only if hygroscopically stable)

EmulsifiableEmulsifiableConcentrateConcentrate

Liquids in WSBLiquids in WSB

Improved ECImproved ECOil in water emulsionOil in water emulsion

Micro-emulsionMicro-emulsionCapsule SuspensionCapsule Suspension

1. Nicotinoids

• History: 1763 for aphids as a ‘tea’ from tobacco

• From: Nicotiana tabacum, N.rustica

• Other sources: – Solanaceae: Duboisia hopwoodii, Anthocercis sp, Cyphanthera

sp, Crenadium sp– Erythroxylum sp, Asclepius syriaca, Anabsis aphylla

• Active constituent: nicotine (alkaloid), nornicotine, anabasine

• Uses: systemic» soft bodied insects eg aphids» almost non-phytotoxic» toxic to humans – only used in confined spaces

• Action: interfere with nerve impulses

Optically active L form most effective

-> Neonicotinoids• Imidacloprid

• Type: chloronicotinyl– Readily absorbed by plants

• Uses: fleas, beetle larvae, termites, many crop pests– Acts quickly on piercing-sucking insects

• Action: neurotoxic to insects» binds irreversibly to post-synaptic nicotinergic acetylcholine

receptors» chlorination inhibits degradation of acetylcholine esterase» toxic to honeybees

• Thiamethoxam

2. Rotenoids• From: roots of

» Derris eliptica, D.malaccensis (Malay peninsula, Burma, Thailand)

» Lonchocarpus utilis (Peru, Brazil)» Tephrosia vogelis (West Africa)

• History: 1649 to paralyse fish, 1848 against caterpillars

• Constituents: isoflavenoids - rotenone» Others: eliptone, deguelin, toxicarol

• Uses: soft bodied insects, red spider, greenfly, caterpillar, wasps

• Action: contact and stomach poison» on mitochondria / electron transfer balance» cause respiratory depression -> paralysis» low human toxicity» some mammalian toxicity – limits its use

• Formulation: insoluble, unstable in alkali

3. Pyrethrins

• From: young flower florets of Chrysanthemum cinerariifolium

• Synonyms: pyrethrum, Dalmatian pyrethrum, Tanacetum cinerariifolium, Pyrethrum cinerariifolium

• Source: Kenya, Tanzania, Rwanda, Equador

• Conditions: 1900-2700m altitude, 76-180cm rainfall

• Market: 1986 13000 tonnes dried flower heads; US$36M

• Transport: baled, mostly powder / standardised liquid extract

• Active constituents: mixed esters» pyrethrin I & II, jasmolin I & II, cinerin I & II

• Action: very rapid paralysis at the nerve ganglia in thoracic region of the insect

» if used with another insecticide -> death» not phytotoxic» not toxic to humans

• Labour intensive picking flowers….

R’

Chrysanthemic acid

Pyrethrolone part

-> Synthetic pyrethroids• Permethrin

• Formulation:» with dipiperonyl butoxide – enhances activity» poor water solubility – with oils or solvents» not very light stable, store in dark, low temps

• Uses: foliar for many crop pests, insect repellant» resistance develops quickly

• Action: neurotoxin, prolongs sodium channel activation» non-toxic to humans» toxic to cats, fish, honeybees

CH3

O

CH2CH=CH2CO2

CH3

CH3

CHC

CH3

CH3

HH

Bioallethrin

C CHCl

ClCH3

CH3

CO2CH OCN

Cypermethrin

Cl CHCO2CH

CH(CH3)2

CNO

Fenvalerate

OCH2CO2

CH3

CH3C

Cl

ClCH

Permethrin

Non Cyano Cyano

• 4. Ryanodine• From: South American plant Ryania speciosa

• Constituent: alkaloid – a complex ester

• Use: traditionally on poison darts» against the codling moth (apple), European corn borer

• Action: binds to ryanodine calcium channel receptors in skeletal/heart muscle

» low concentrations locks the receptor half open» higher concentrations causes influx of calcium from

sarcoplasmic reticulum

• Biodegradable, deleafs forests

• 5. Quassia

• Wood (simple) extract of Quassia amara

• Saponins – good against aphids

• Use may revive due to aphid resistance

• 6. Cevadilla (sabadilla) seed• From: Schoenocaulon officinale, Mexico to Venezuela

• Constituents: mixed alkaloids ‘veratrine’» main ones: cevadine, veratridine

• Uses: controls thrips and true bugs that attack vegetables» powdered seeds or veratrine preparations used a dust or

spray

• Action: increases sodium permeability of axons

• 7. Tar oils• From wood of pine and juniper

• Used a long time

• Very phytotoxic» only used on dormant plants ‘winter wash’» eg fruit trees, rose bushes

• Acts on most fungal pests as well as insects

• Cheap and effective

• 8. Acorus calamus• Rhizome and leaf oils

• Constituents: asarone (β and α), linalool

• Use: by the Chinese a long time» against diamond-backed moth

• Action: may have anti-juvenile hormone activity

• 9. Neem• From: Azadirachta indica

» margosa (seed) oil, leaf extracts

• Constituents: 25+ active compounds» limonoids (nortriterpinoids) - azadirachtin

• Use: believed to work against many insects» including borers, leaf beetles, fruit flies

• Action:» Anti-feedent: suppresses the insect's desire to feed and,

therefore, no damage is caused » Repellent: Insects simply stay away from areas sprayed

with Neem and, therefore, no damage is caused » Insect Growth regulator: Neem disrupts the insect's

delicate hormonal balance so it dies before it molts to the next life stage

• Formulation: applied as a foliar spray or as a soil drench for systemic control

• 10. Sucrose octanoate esters• Sucrocide: found on tobacco leaf hairs• Action: dissolves insect exoskeleton• Use: aphids, leafhoppers, bugs, caterpillars, mites

• 11. Other plants• Anethum graveolens (dill)• Nigella sativa (black cumin)

– concentration dependent inhibition of » larvae -> pupae» pupae -> adult

– against red wheat flour beetle – by fumigation of essential oil from fruits

• Pistia stratiotes• Cyperus rotandus

– please find information!

• Desmodium caudatum• Oregano

12. Spinosads (spinosyn A, D)• New: chemical class of natural insecticide, novel action

• From: Saccharapolyspora spinosa, rare actinomycetes or soil fungus – fermentation products

• Uses: contact and stomach activity, good larvicidal» fruit flies, caterpillars, leafminers, thrips, termites, sawflies,

spider mites, leaf beetle larvae» long residual activity

• Action: disrupts binding of ACh in post-synaptic nicotinic acetylcholine receptors causing overstimulation of the nervous system

» low toxicity for mammals» highly toxic for bees» non-phytotoxic for most crops

13. Mectins• From:

– Steptomyces avermitilis – fermentation products– Abamectin

» local systemic qualities permitting it to kill mites in leaf’s underside when only upper surface is treated

» -> analogs: avermectin, emamectin, milbemectin– Emamectin

» contact and stomach insecticide» lepidopterus larvae

• Use: insecticidal, acaricidal, nematicidal

• Action: block GABA at the neuromuscular junction» visible activity soon after exposure» death may not occur for several days

• 14. Kaolin Clay• From: Kaolinite (China clay)

– a mineral clay– Al2Si2O5(OH)4

• Formulation: spray– on fruit, vegetables

• Action: creates a physical barrier– irritates the mouthparts of chewing insects– prevents oviposition (egg laying)

• Use: for boring or mining larvae

• 15. Diatomaceous earth• Diatomite, Kieselguhr• naturally occurring soft chalk-like sedimentary rock

– fossilised remains of hard-shelled algae, diatoms– very porous– typically 86% silica, 5% sodium, 3% magnesium, 2% iron

• Action: physico-sorptive properties– Insects: fine powder absorbs lipids from their cuticle ->

dehydration– Gastropods: also works against eg snails/slugs