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Arthropod Environmental Management 2 Topics for Session 2 Botanical Insecticides Sabadilla, Nicotine, Ryanodine, Quassia, Rotenone, Pyrethrum, Neem Extracts,

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Presentation on theme: "Arthropod Environmental Management 2 Topics for Session 2 Botanical Insecticides Sabadilla, Nicotine, Ryanodine, Quassia, Rotenone, Pyrethrum, Neem Extracts,"— Presentation transcript:

1 Arthropod Environmental Management 2 Topics for Session 2 Botanical Insecticides Sabadilla, Nicotine, Ryanodine, Quassia, Rotenone, Pyrethrum, Neem Extracts, Essential Oils Synthetic Insecticides Organochlorides, Pyrethroids, Organophosphates, Carbamates, Neonicotinoids Growth Regulators Moulting hormone mimics, Juvenile hormone mimics, Chitin Synthesis Inhibitors

2 Arthropod Environmental Management 2 Botanical Insecticides Phytochemicals (plant chemicals) Often Secondary Plant Substances (in contrast to primary substances) Examples include alkaloids (eg nicotine), phenolic compounds, and terpenoids Use dates back ca years (continues in native cultures) Western use since 16 th C explorations

3 Arthropod Environmental Management 2 Botanical Insecticides – Current Interest Cost of developing new insecticides Small proportion of plants evaluated Previous success with carbamates and pyrethroids Newer successes with neonicotinoids and with neem extracts Still used in native cultures

4 Arthropod Environmental Management 2 (some) Plants Still Used in Native Cultures for Pest Control Custard Apple, Sweet Flag, Chrysanthemum, Spearmint, Derris, Garlic, Sabadilla, Neem, Quassia, Chilli, Turmeric Some authors suggest that ca. 2,400 species are used at the local level

5 Arthropod Environmental Management 2 Botanical Insecticides – Issues with Commercial Development Farmers regard botanicals as old-fashioned Not on official lists Often do not get dramatic kills of pests Light and Air may inactivate May be seasonal availability Costs may be high May be of variable toxicity

6 Arthropod Environmental Management 2 Botanical Insecticides - Examples Sabadilla Nicotine Ryanodine Quassia Rotenone Pyrethrum Neem Extracts Essential Oils

7 Arthropod Environmental Management 2 Sabadilla Powdered seeds used by S. American Indians to protect crops from insect attack (from Sabadilla officinarum – a plant in the Lily family) Discovered by European explorers Exported to Europe from 16 th C to WWII (over 120,000 tonnes to USA in 1940s, use declined because of advent of DDT) Actives are alkaloids, rapidly inactivated by exposure to sunlight and air (as are many botanicals)

8 Arthropod Environmental Management 2 Sabadilla Contact and Stomach poison that is neurotoxic (sodium channels). This is similar to DDT and the pyrethroids Good for pre-harvest treatments (because it is rapidly inactivated) Use has largely been phased out because of cheaper alternatives, cannot be synthesised, must be extracted – still used in native cultures

9 Arthropod Environmental Management 2 Nicotine Alkaloid nicotine from tobacco plants Discovered by European explorers, in use by American Indians By 17 th /18 th Century widely used in Europe AI was named nicotine in 1828, in 1904 it was chemically synthesised

10 Arthropod Environmental Management 2 Nicotine Contact insecticide that works as an agonist for acetylcholine receptors on post-synaptic membranes Not very selective (high mammalian toxicity in contrast to sabadilla), rapidly inactivated (48 hrs) Still available for use in Europe in professional situations More costly than modern synthetics so use largely phased out (originally made from low grade tobacco) Like sabadilla is still used in native cultures

11 Arthropod Environmental Management 2 Quassia From Central American tree Quassia amara Exported from 18 th C to WWII to Europe (from commercial plantations in Venezuela) Contact and stomach poison from bark and branches. Active ingredient is called quassin. Has not yet been synthesised

12 Arthropod Environmental Management 2 Quassia May have some systemic activity (nicotine and sabadilla do not, they are contact and stomach poisons) Has not been synthesized and exact mode-of- action not clear Like most botanicals it is too costly in comparison to modern chemicals Still used in native cultures and there is a revival of interest in quassia in the West.

13 Arthropod Environmental Management 2 Ryanodine First botanical to be discovered as a result of an official screening programme (in 1940s in USA) Active is an alkaloid from a South American shrub in the genus Ryania It is a contact/stomach poison and is much more stable than other botanicals (up to a week)

14 Arthropod Environmental Management 2 Ryanodine Mode-of-action is to bind to calcium channels. Cells then are flooded with calcium molecules and poisoned species die It has a moderate mammalian toxicity (750mg/kg in contrast to more than 4,000 for sabadilla and to 50 for nicotine) It cannot be synthesised and so costs associated with its commercial production are prohibitive. Still used in native cultures.

15 Arthropod Environmental Management 2 Rotenone Extracts from plants of American & Asian origin (unlike other botanicals) Used in native cultures as fish poison Used in Western countries from 1840s but has now declined because of cheaper alternatives

16 Arthropod Environmental Management 2 Rotenone Chemical structure was determined in 1930s. At least 10 related chemicals called rotenoids have now been described from over 70 different plant species. Cannot be synthesised. AIs disrupt mitochondria reducing oxygen uptake so poisoned species suffocate. Is of moderate mammalian toxicity Rapidly inactivated by exposure to light and air In 2000 could still buy amateur and professional formulations in the UK. Still used in native cultures

17 Arthropod Environmental Management 2 Pyrethrum Best known botanical. From Chryanthemum. Extracts from flower heads Use since start of 19 th C to present. Still used today. Kenya and Tanzania grow most of the plants that are used commercially Very unstable, good pre-harvest and safe to use in domestic situations

18 Arthropod Environmental Management 2 Pyrethrum Natural pyrethrins are a mixture of AIs. All are contact insecticides that act on sodium channels. Mammalian toxicity is 1,600 mg/kg. Synthetic versions of natural pyrethrins have now been produced (first in 1949/1950 was an AI called Allethrin)

19 Arthropod Environmental Management 2 Neem Extracts Extracts from Asian neem tree. Main active is thought to be azadirachtin These trees are now grown throughout the world including the USA (plantations in California and in Florida) Best extracts from seed but all plant parts have been used Azadirachtin cannot be synthesised. Full chemical structure published in 1985

20 Arthropod Environmental Management 2 Neem Extracts Main AI is azadirachtin but further AIs are continually being discovered, e.g. nimbin and sallanin. Crude extracts always more potent than azadirachtin. Since 1990s has been increasing interest in these extracts and a number of formulations now exist Works by disrupting development of larvae (hormonal interference) and as an antifeedant (has systemic activity). Very high mammalian toxicity (> 5,000 mg/kg) Inactivated by sunlight. Interest in neem formulations continues to grow

21 Arthropod Environmental Management 2 Essential Oils Many are recorded as having insecticidal activity, primarily as repellents rather than as toxicants Most well known are eucalyptus, peppermint and citronella Most are highly volatile and are extracted in such small amounts that they are uneconomic to develop on a large scale Still used in native cultures

22 Arthropod Environmental Management 2 Botanicals - Summary Most success with Pyrethrum, neem is of current interest All contact/stomach poisons except neem and quassia extracts (systemic) Most act of nervous system, some on respiration (rotenone), some on development (neem) Most are unstable (except ryanodine) and difficult to synthesise (except pyrethroids and nicotine)

23 Arthropod Environmental Management 2 Botanicals – Questions?

24 Arthropod Enviornmental Management 2 Chemical Insecticides Organochlorides Pyrethroids Organophosphates Carbamates Neonicotinoids Growth Regulators

25 Arthropod Environmental Management 2 Organochloride Insecticides First extensively used group of insecticides Comprised of three groups: DDT group, HCH group, and cyclodienes

26 Arthropod Environmental Management 2 Organochloride Insecticides - DDT DDT (DichloroDiphenylTrichloroethane) First prepared in 1874, insecticidal properties discovered in 1939 Used during war to control vectors of malaria and typhus (mosquitoes and fleas) 1948 – Paul Muller was awarded Nobel prize for medicine for his discovery of DDT Cheap and stable molecule Now banned throughout Europe and other Western countries

27 Arthropod Environmental Management 2 Organochloride Insecticides - DDT Fat soluble (lipophilic) so biomagnifies or bioconcentrates Species GroupDDT ConcentrationConcentration Factor Water ppmnot applicable Zooplankton0.04 ppmca. 13,000 Small Fish0.5 ppmca. 17,000 Large Fish2 ppmca. 700,000 Fish-Eating Birds25 ppmca. 8 million

28 Arthropod Environmental Management 2 Organochloride Insecticides - DDT Toxicity of DDT DDT appears to disrupt calcium metabolism in birds leading to egg-shell thinning This caused particular problem for predatory birds (e.g. eagles) Main mode-of-action is as neurotoxin Interferes with sodium channels on nerve axons Is a contact/feeding poison with no systemic activity Still used in Africa and Asia for mosquito control

29 Arthropod Environmental Management 2 Organochloride Insecticides - Summary Extremely stable group, half lives measured in years Chemically composed of C, H, and CL groups 10 – 20 actives developed are marketed No longer used in Western countries, most used in developing countries They are cheap, stable and effective, especially for control of vectors of disease

30 Arthropod Environmental Management 2 Pyrethroid Insecticides Synthetic pyrethroids First was marketed in 1950 (allethrin), since then ca. 30 AIs have been produced. Examples include permethrin, deltamethrin, cypermethrin Synthetic development has focussed on stabilising the natural version (pyrethrum) of the active molecule

31 Arthropod Environmental Management 2 Pyrethroid Insecticides Comparisons between pyrethum and synthetic versions

32 Arthropod Environmental Management 2 Pyrethroid Insecticides Comparisons between pyrethum and synthetic versions

33 Arthropod Environmental Management 2 Pyrethroid Insecticides Comparisons between pyrethum and synthetic versions Much more photostable, sites of auto-oxidative attack removed. Natural pyrethrum open to hydrolytic, esteratic and oxidative attack Synthetic chemicals are cheaper to produce Much more toxic than natural pyrethrum, can be applied at far lower application rates

34 Arthropod Environmental Management 2 Pyrethroid Insecticides – Mode of Action Contact & stomach poisons, no systemic activity Interfere with sodium channels on nerve axons (like DDT) Have a rapid knock-down effect suggesting that the peripheral nervous system is affected immediately

35 Arthropod Environmental Management 2 Organophosphate Insecticides Developed from wartime research on potential nerve agents (sarin and tabun) First insecticide was schradan (now replaced), 80 – 100 AIs developed All tri-esters of phosphoric acid

36 Arthropod Environmental Management 2 Organophosphate Insecticides Break down in days – weeks Some are systemic Examples of OPs include malathion, parathion, chlorpyrifos Very widely used group of insecticides worldwide

37 Arthropod Environmental Management 2 Organophosphate Insecticides Mode of Action Neurotoxins – interfere with synaptic transmission of nerve impulses Block the enzyme that breaks down acetylcholine Acetylcholinesterase binds OPs and the neurotransmitter builds up in synapses In human poisoning the acetylcholine inhibitor atropine is administered

38 Arthropod Environmental Management 2 Carbamate Insecticides First (carbaryl) marketed in 1956 Developed from knowledge that a natural carbamate (physostigmine) had anti- cholinesterase activity Ca. 30 AIs developed, all with an N-methyl carbamate group

39 Arthropod Environmental Management 2 Carbamate Insecticides Physostigmine is very hydrophilic, synthetic carbamates are much more lipophilic Examples include pirimicarb and aldicarb, the most toxic insecticide marketed to date Overall, their use is declining but they are still widely available.

40 Arthropod Environmental Management 2 Carbamate Insecticides – Mode of Action Like OPs they block the enzyme acetylcholinesterase The process is called carbamylation (rather than phosphorylation) Like OPs atropine is used in cases of poisoning

41 Arthropod Environmental Management 2 Carbamate Insecticides – Bhopal 1984 – factory in India producing carbaryl released a cloud of Methyl Isocyanate Of the 800,000 people living in Bhopal, 2,000 died immediately, at least 10,000 have died subsequently and at least 300,000 people were affected This remains the worlds worst industrial accident where human lives are concerned In 1989 a final settlement was supposed to have been reached ($470 million) Many people think that more still needs to be done – Bhopal is still contaminated

42 Arthropod Environmental Management 2 Neonicotinoids Newest group of synthetic insecticides Imidacloprid was marketed in 1991, now 4 others available All have contact and systemic activity Based on the alkaloid nicotine

43 Arthropod Environmental Management 2 Neonicotinoids Like nicotine they work as agonists to acetylcholine This leads to a build up of acetylcholine which causes death Now one of the most extensively used group of insecticides worldwide

44 Arthropod Environmental Management 2 Synthetic Insecticides - Summary EnvironmentalExposureNumber Stabilityand Toxicityof A.I.s OrganochloridesMonths toContact &ca YearsFeeding Poisons. OrganophosphatesWeeksContact, Feedingca & Systemic Poisons PyrethroidsWeeksContact &ca Feeding Poisons CarbamatesWeeksContact, Feedingca & Systemic Poisons NeonicontinoidsWeeksContact, Feedingca. 5-7 & Systemic Poisons

45 Arthropod Environmental Management 2 Insect Growth Regulators Chemicals that affect growth and development Usually applied through conventional application equipment Mostly effective against juvenile stages (timing important) Three groups: juvenile hormones, moulting hormones, chitin synthesis inhibitors

46 Arthropod Environmental Management 2 Insect Growth & Development All arthropods have exoskeletons (support, movement & prevent dehydration) These must be shed to grow, a process controlled by hormones Moulting hormone: determines whether a moult occurs Juvenile hormone: determines type of moult Studies on hormones for back 40 years (not new)

47 Arthropod Environmental Management 2 Juvenile Hormone (JH) Mimics Studies on plant extracts (firs & ferns) indicated compounds with JH activity Led to production of farnesol (first synthetic hormone) Keeps insects in juvenile stage (limited use), does not penetrate cuticles well Some commercial successes: kinoprene, methoprene

48 Arthropod Environmental Management 2 Juvenile Hormone (JH) Mimics Most uses against pests of public and animal health (i.e. fleas) Break down fairly rapidly on exposure to light and air Compounds with Anti-JH activity have been developed but none sufficiently active

49 Arthropod Environmental Management 2 Moulting Hormone (MH) Mimics MH causes a moult to occur Can be used against juvenile stages Examples include: tebufenozide, halofenozide They cause a precocious moult to occur in treated pest species Used against a range of pest species

50 Arthropod Environmental Management 2 Chitin Synthesis Inhibitors Most successfully developed group of IGRs > 10 formulations marketed All cause a reduction in chitin synthesis (structural polysaccharide) Disrupt the enzyme chitin synthetase Insects die from dehydration, predation, etc. Very successfully used in locust control operations in Africa

51 Arthropod Environmental Management 2 Insect Growth Regulators – Summary Most success with CSIs (only effective against juveniles, adults do not moult!) Some other successes with MH and JH mimics, particularly for control of public health pests All highly specific with zero impact on vertebrates Overall, still a relatively small section of pest control market


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