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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)

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S2 l2 insecticides natural l.jpg

S2 L2 Insecticides - natural

Anna Drew

with slide contribution from Martin Wilks, Syngenta,

& Rhonda Hamm

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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

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Importance of Pesticide Regulation

PESTICIDEREGULATION 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.

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Stages of Risk Assessment

Toxicological Hazard Assessment

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

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World Health Organization (WHO)Classification of Pesticides by Hazard


for the rat (mg/kg body weight)









Ia Extremely

5 or less

20 or less

10 or less

40 or less


Ib Highly

5 - 50

20 - 200

10 - 100

40 - 400


II Moderately

50 - 500

200 - 2000

100 - 1000

400 - 4000


III Slightly

Over 500

Over 2000

Over 1000

Over 4000


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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)

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Stages of Risk Assessment Pesticide Operators

Toxicological Hazard Assessment



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

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The Dose Response Curve Pesticide Operators

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Stages of Risk Assessment Pesticide Operators

Toxicological Hazard Assessment



Human Exposure


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

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Stages of Risk Assessment Pesticide Operators

Toxicological Hazard Assessment



Human Exposure


Risk Characterisation

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

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Toxicology Information in the Development Process Pesticide Operators



  • Physico-chemical properties

  • Acute oral toxicity, mutagenicity

  • Dermal absorption, inhalation toxicity

  • Subacute & subchronic toxicity

  • Reproductive & developmental toxicity

  • Chronic toxicity, carcinogenicity

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Evolution of Crop Protection Product Formulations Pesticide Operators

Soluble Liquid

Soluble and stable in water


Wettable Powder

Solid or unstable in water


SC (suitable only if hygroscopically stable)

Liquids in WSB



Oil in water emulsion

Soluble in organic solvent

Improved EC


Capsule Suspension

1960 1970 1980 1990 2000

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1. Nicotinoids Pesticide Operators

Optically active L form most effective

  • 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

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    -> Neonicotinoids Pesticide Operators

    • 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

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    2. Rotenoids Pesticide Operators

    • 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

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    3. Pyrethrins Pesticide Operators

    • 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

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    Chrysanthemic acid Pesticide Operators

    • 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….

  • Pyrethrolone part


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    -> Synthetic pyrethroids Pesticide Operators

    • 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

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    Non Cyano Pesticide Operators






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    • 4. Ryanodine Pesticide Operators

      • 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

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    • 5. Quassia Pesticide Operators

      • 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

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    • 7. Tar oils Pesticide Operators

      • 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

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    • 9. Neem Pesticide Operators

      • 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

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    • 10. Sucrose octanoate esters Pesticide Operators

      • 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

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    12. Spinosads (spinosyn A, D) Pesticide Operators

    • 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

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    13. Mectins Pesticide Operators

    • 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

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    • 14. Kaolin Clay Pesticide Operators

      • 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

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    • 15. Diatomaceous earth Pesticide Operators

      • 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