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Insecticides A Brief Overview of a Complex Subject.

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Presentation on theme: "Insecticides A Brief Overview of a Complex Subject."— Presentation transcript:

1 Insecticides A Brief Overview of a Complex Subject

2 Modes of Entrance into Insect Contact - dermal – through the skin Stomach - oral – through the mouth Respiration - inhalation through the nose or gills Systemic - combination of above

3 Mode of Toxicity in Insects Physical poison General protoplasmic poison Cellular enzyme poison Nerve poison Growth regulator Disease causing agent Repellant

4 Toxicity to humans or nontarget organisms Most insecticides have the capacity to affect non-target organisms Same as previously discussed  Highly toxic – LD 50 0 – 50 mg/kg  Moderately toxic - LD – 500 mg/kg  Low toxicity - LD – 5,000 mg/kg  Nontoxic - LD 50 <5,000 mg/kg

5 Toxicity to insects natural enemies Most insecticides have the potential to affect populations of beneficial insects.

6 Toxicity to insects natural enemies Highly toxic - Pest populations recover much faster than enemy populations in nature

7 Toxicity to insects natural enemies Moderately toxic – Pest populations recover somewhat faster than enemy populations in treated environment

8 Toxicity to insects natural enemies Low toxicity – Natural enemies are maintained to a degree & quickly attack recovering pest populations

9 Toxicity to insects natural enemies Nontoxic – Normal enemy population levels are maintained which quickly attack recovering pest populations

10 Environmental hazard Environmental hazard of insecticides is generally evaluated as a function of persistence often compared to effectiveness

11 Environmental hazard High – Environmental persistence far greater than period of effectiveness (> 5 months and often > a year)

12 Environmental hazard Intermediate – Persists beyond effectiveness (3-5 month half-life)

13 Environmental hazard Low – Persists about the period of effectiveness (up to about 3 months) and then degrades completely over several months

14 Environmental hazard Very low – Persists for short periods (>45 days) and degrades completely

15 Resistance/Resurgence Hazard The hazard of populations developing resistance and resurging is evaluated for most insecticides

16 Resistance/Resurgence Hazard High – Strong potential to develop resistance and resurge

17 Resistance/Resurgence Hazard Intermediate – Moderate potential to develop resistance in treated environments

18 Resistance/Resurgence Hazard Low – Minimal potential to develop resistance

19 Resistance/Resurgence Hazard None – No resistance developed, no resurgence after many treatments

20 IPM Attributes IPM is especially important when discussing the use of insecticides due to the potential for the development of resistance and subsequent resurgence of pest populations repeatedly treated with a single insecticide Repeated treatment with a single pesticide imposes artificial genetic selection on insect populations

21 IPM Attributes However, IPM must be effective and so there are several criteria to evaluate  Effectiveness in controlling pest populations  Cost of treatment  Human and nontarget-animal toxicity  Environmental persistence

22 Insecticide groups The following slides present a system in which insecticides are generally catagorized It is not the only system Lumpers and splitters of names have created very different categories, depending on their emphasis

23 Organochlorines Also called the chlorinated hydrocarbon insecticides

24 Organochlorines Characterized by containing chlorine and carbon atoms

25 Organochlorines Powerful nerve poisons

26 Organochlorines Most affect a broad spectrum of non- target organisms along with the target pests

27 Organochlorines Biochemical mode of action – uncertain

28 Organochlorines Mode of action chemical dependant

29 Organochlorines Long persistence and residual activity

30 Organochlorines Several were used in forestry  DDT  Lindane  Dicofol (Kelthane)  Endosulfan (Thiodan)

31 Organochlorines Most have been banned in the U.S.

32 Organochlorines Very few still available for our use  Endosulfan is sometimes used on ornamentals and in seed orchards  Lindane is still registered for Southern Pine Beetle control but no product is available in the marketplace

33 Organophosphates Also known as the OPs

34 Organophosphates Characterized by containing carbon and phosphorus atoms

35 Organophosphates Chemical and often habitat dependant effect on non-target organisms

36 Organophosphates Mode of action varies by chemical

37 Organophosphates Generally only short term persistence and limited residual activity

38 Organophosphates Unfortunately, often have broad spectrum activity against beneficial insects

39 Organophosphates Several used in forestry or applied to forests for public health purposes  Malthion (Malathion and Cythion)  Acephate (Orthene)  Methyl parathion (Methyl parathion)  Diazinon (Diazinon and Spectracide)  Chlorpyrifos (Dursban and Lorsban)  Azinphos methyl (Guthion)

40 Organophosphates Most have been lost to forestry due to FQPA (Food Quality Protection Act) review performed by the EPA

41 Organosulfurs Small group of sulfur containing insecticides

42 Organosulfurs Low insect toxicity, but with good miticidal characteristics

43 Organosulfurs Have been used in seed orchard work

44 Organosulfurs Only a single product relevant to this discussion  Propargite (Omite)

45 Carbamates Insecticides which are derivatives of carbamic acid

46 Carbamates Non-target toxicity is chemical specific, ranging from low to very high

47 Carbamates Generally only short term persistence and limited residual activity

48 Carbamates Often with broad spectrum activity against beneficial insects

49 Carbamates Very few used in forestry  Carbaryl (Sevin)  Aldicarb (Temik)  Methomyl (Lannate)

50 Botanicals Chemicals extracted or derived from plants

51 Botanicals May be present and subsequently extracted from the plant material (a constitutive chemical), or

52 Botanicals May be activated in the plant as a response to insect activity (inducible chemicals)

53 Botanicals Limited numbers of extractable chemicals have performed well enough to have been made commercially available

54 Botanicals Some are chemically modified after extraction to enhance their insecticidal properties

55 Botanicals Only a few have found a niche in forestry, and generally even these are subsequently replaced by more target- specific, less persistent synthetic chemicals  Pyrethrins  Resmethrin (Pyosect, Synthhrin)  Azadirachtin (Azatin)

56 Synthetic Pyrethroids Modified esters of chrysanthemate a chemical similar to that which is derived from chrysanthemums

57 Synthetic Pyrethroids Alterations in the acid components yield a reduced degradation rate compared to natural pyrethrins

58 Synthetic Pyrethroids Often with additional modification to enhance synergistic action

59 Synthetic Pyrethroids Rates are often 10% of the rates of OPs

60 Synthetic Pyrethroids Several have been used in forestry, seed orchard or nursery work  Permethrin (Pounce, Ambush, Dragnet)  Cypermethrin (Ammo)  Esfenvalerate (Asana)  Lamda cyhalothrin (Karate)

61 Synergists or activators Chemicals which perform any of a variety of actions which enhance the action of an insecticide

62 Synergists or activators Increase the toxicity of the initial chemical above that expected from the combination of the two products  Block detoxification of insecticides by insect defensive systems  Induce the functioning of otherwise benign chemicals

63 Synergists or activators Two primary chemicals used in insecticide formulation  Piperonyl butoxide  Sesamin

64 Soaps and Abrasives Produced by rending (cooking) animal fat (lard), fish oil or vegetable oil with an alkali metal such as sodium hydroxide (= hard soap) or potassium hydroxide (= soft soap)

65 Soaps and Abrasives Soft soaps from fish oils were the most common insecticidal soaps in the past since they are the most effective insecticidal soaps

66 Soaps and Abrasives Soft soaps made from vegetable oils are most common at the present time due to a better smell (not greater efficacy)

67 Soaps and Abrasives Soften or wash off the waxy epicuticle covering an insect allowing it to dehydrate

68 Soaps and Abrasives Abrasives degrade the epicuticle - same result

69 Soaps and Abrasives Two soaps are commonly used  Potassium salts of fatty acids (Safer soaps, M-Pede)  Boric acid

70 Soaps and Abrasives A single abrasive is currently registered as a forestry insecticide  Borax

71 Microbial Pathogens Fungi, bacteria, viruses, etc. which can be used to cause disease in an insect population

72 Microbial Pathogens Relatively narrow spectrum of activity, not broad spectrum insecticides

73 Microbial Pathogens Several have been genetically engineered to kill target insects more rapidly

74 Microbial Pathogens Bacteria in forestry  Bacillus thuringiensis var. karstaki (Dipel, Thuricide, Foray, Agrobac, Javelin, Cutlass)

75 Microbial Pathogens Virus in forestry  Baculovirus (Nucleopolyhedrosis virus or NPV; Gypchek, TM- Biocontrol-1)

76 Microbial Pathogens Bacteria applied over forests for public health protection  Bacillus thuringiensis var. israeliensis  Bacillus sphaericus

77 Microbial Derivatives Generally organic chemicals with a nitrogen component

78 Microbial Derivatives Microbially produced and then extracted and refined

79 Microbial Derivatives Some are toxic to the target organisms at very low doses

80 Microbial Derivatives Only one used in forestry at present  Avermectin (derived from Streptomyces avermitilis)  Also available are: spinosad (Tracer) pyrroles (Pirate)

81 Repellants Large group of unrelated chemicals

82 Repellants Many experimental chemicals – but to the present no truly effective forest protectant chemical

83 Repellants Mostly have found use for people or livestock protection

84 Repellants Forestry insect repellants include  Verbenone  4-allyl anisole (4AA) Both are anti-aggregant chemicals designed to disrupt pine beetle aggregation and thwart ‘spot’ formation

85 Repellants Forester protective repellant  Deet (Off, Deep-Woods-Off)

86 Oils Lightweight petroleum oils mixed with emulsifiers may be used as insecticides in some cases

87 Oils Broadly defined in two groups:  Dormant oils are designed to be used to protect dormant plant materials and may have bad effects if used during the growing season  Summer oils may be used to protect growing plants

88 Oils Oils kill by suffocation (scales, mealy bugs and aphids)

89 Oils Forestry registered oils include  Sunspray  Superior oil

90 Fumigants Primarily used in forest tree nursery beds and greenhouses

91 Fumigants Fumigants generally contain a halogen (chlorine, bromine, fluorine, etc.) in their molecules

92 Fumigants Small molecules which vaporize at relatively low temperatures

93 Fumigants Many are now or will shortly be banned in the US

94 Fumigants Fumigants which have held forestry or ornamental insecticide registration  Methyl bromide (MC33, MC98, Brom-o- Sol, etc.) – NFTA should eliminate this fumigant from the US by 2005  Dichloropropene  Chloropicrin  Metam-sodium (Vapam, Busan, Sectagon)

95 Transgenic Crops with Insecticidal Properties Plants genetically engineered to enhance insecticidal properties

96 Transgenic Crops with Insecticidal Properties None in forestry as yet


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