Insecticides A Brief Overview of a Complex Subject

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

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

Toxicity to humans or nontarget organisms Most insecticides have the capacity to affect non-target organisms Same as previously discussed Highly toxic – LD50 0 – 50 mg/kg Moderately toxic - LD50 50 – 500 mg/kg Low toxicity - LD50 500 – 5,000 mg/kg Nontoxic - LD50 <5,000 mg/kg

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

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

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

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

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

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

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

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

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

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

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

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

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

Resistance/Resurgence Hazard Low – Minimal potential to develop resistance

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

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

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

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

Organochlorines Also called the chlorinated hydrocarbon insecticides

Organochlorines Characterized by containing chlorine and carbon atoms

Organochlorines Powerful nerve poisons

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

Organochlorines Biochemical mode of action – uncertain

Organochlorines Mode of action chemical dependant

Organochlorines Long persistence and residual activity

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

Organochlorines Most have been banned in the U.S.

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

Organophosphates Also known as the OPs

Organophosphates Characterized by containing carbon and phosphorus atoms

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

Organophosphates Mode of action varies by chemical

Organophosphates Generally only short term persistence and limited residual activity

Organophosphates Unfortunately, often have broad spectrum activity against beneficial insects

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)

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

Organosulfurs Small group of sulfur containing insecticides

Organosulfurs Low insect toxicity, but with good miticidal characteristics

Organosulfurs Have been used in seed orchard work

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

Carbamates Insecticides which are derivatives of carbamic acid

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

Carbamates Generally only short term persistence and limited residual activity

Carbamates Often with broad spectrum activity against beneficial insects

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

Botanicals Chemicals extracted or derived from plants

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

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

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

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

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)

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

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

Synthetic Pyrethroids Often with additional modification to enhance synergistic action

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

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

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

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

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

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)

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

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

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

Soaps and Abrasives Abrasives degrade the epicuticle - same result

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

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

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

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

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

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

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

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

Microbial Derivatives Generally organic chemicals with a nitrogen component

Microbial Derivatives Microbially produced and then extracted and refined

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

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

Repellants Large group of unrelated chemicals

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

Repellants Mostly have found use for people or livestock protection

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

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

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

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 l

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

Oils Forestry registered oils include Sunspray Superior oil

Fumigants Primarily used in forest tree nursery beds and greenhouses

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

Fumigants Small molecules which vaporize at relatively low temperatures

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

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)

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

Transgenic Crops with Insecticidal Properties None in forestry as yet