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
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
Organochlorines • Also called the chlorinated hydrocarbon insecticides • Characterized by containing chlorine and carbon atoms • Powerful nerve poisons • Most affect a broad spectrum of non-target organisms along with the target pests • Long persistence and residual activity
Organochlorines • Several were used in forestry • DDT • Lindane • Dicofol (Kelthane) • Endosulfan (Thiodan)
Organophosphates • Also known as the Ops • Characterized by containing carbon and phosphorus atoms • Generally only short term persistence and limited residual activity • 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)
Organosulfurs • Small group of sulfur containing insecticides • Low insect toxicity, but with good miticidal characteristics
Carbamates • Insecticides which are derivatives of carbamic acid • Non-target toxicity is chemical specific, ranging from low to very high • Generally only short term persistence and limited residual activity • 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 • May be present and subsequently extracted from the plant material (a constitutive chemical), or • May be activated in the plant as a response to insect activity (inducible chemicals)
Botanicals • Some are chemically modified after extraction to enhance their insecticidal properties
Botanicals • Pyrethrins • Retenone • Ryaia
Botanicals • Pyrethrins • Very toxic to cooled blooded animals, some peoples and cats. • Very effective on most insects. • it rapidly breaks down in sunlight, air and water.
Botanicals • Retenone • Derived from the roots of over 68 plant species and is very toxic to fish, pigs, and cool blooded animals • Used to control leaf eating caterpillars and beetles • Direct contact may cause skin and mucus membranes irritation.
Botanicals • Ryaia • Botanical insecticides made from the ground stem of Ryana speciosa • Ishighly toxic to the fruit moths, and citrus thrips
Nicotine • Nicotine a plant defense alkaloid • Nicotine is a fast acting contact killer for soft bodies but does not kill most chewing insects. • Concentrate is very poisons if inhaled. • Highly toxic to warm blooded animals. • Pale yellow to dark brown liquid.
Nicotine • The effectiveness is similar that of organophosphorous compounds • Nicotine inhibits the function of acetylcholine receptors located at the neuromuscular junctions. • Nicotine is highly lipophilic and can pass through dermal tissues as well as the blood brain barrier.
Essential oils • Some plants also produce essential oils in specialized gland cells:- • Peppermint oil( (زيت روح النعناعcontrol of household pests such as cockroaches and ants. • Clove oil((كبش قرنفلinhibit soil born fungal disease. • Citrus oil control of flea, aphid and mites • Lavender oil insect repellent. • Thyme oil • Rosemary oil • Cedar oil--
Microbial Pathogens • Fungi, bacteria, viruses, etc. which can be used to cause disease in an insect population • Relatively narrow spectrum of activity, not broad spectrum insecticides • Several have been genetically engineered to kill target insects more rapidly
Microbial Pathogens • Bacillus thuringiensisBacillus Sphaericus • Baculovirus
Repellants • Large group of unrelated chemicals • Many experimental chemicals – but to the present no truly effective forest protectant chemical • Mostly have found use for people or livestock protection
Repellants • Repellent for foliage feeders • (مواد طاردة للحشرات التي تتغذى على الاوراق النباتية) • Such as:- • bordeaux mixture • (copper sulfate, hydrate lime, water) • Repelles of beetles and grasshoppers • Copper ions affect enzymes in the fungal spores in such a way as to prevent germination.
Repellants • Repellents for crawling insect • المواد الطاردة للحشرات الزاحفة • Such as:- • Cresol ( organic compound, used as disinfectants) • Trichlorobenzene (effect for along time, repelled white ants) • Repellents to fabric eating insects • المواد الطاردة للحشرات التي تتغذى على المواد المصنعة
Repellants • repellents to blood sucking insects • Such as:- • Dimethyl phthalate ( anopheles, aedes, culex) • 2-Ethyl-1.3- hexonediol ( house fly, mosquito, flea) • DEET( applied to skin and cloths and is used to repel mosquitoes) • Citronella oil ( personal insect repellents such as mosquito) • Oil of lemon Eucalyptus ( active against mosquito)
الشروط الواجب توافرها في المواد الطاردة • 1- ان لاتسبب حساسية لجلد الانسان و الحيوان • 2- الا ينتج عن استعمالها رائحة غير مقبولة و ان لا يكون لها تاثير على الملابس • 3- ان تعطي حماية لمدة طويلة بتركيزات منخفضة • 4- ان تكون رخيصة الثمن و يمكن الحصول عليها بسهولة • 5- الا يكون لها تأثير سام على الانسان و الحيوان • 6- ان يبقى مفعولها لمدة طويلة • 7- يجب ان يكون لها تاثير طارد لانواع عديدة من الحشرات • 8-يجب ان لا يفقد مفعولها بسرعة بواسطة عرق الانسان
Fumigants • Fumigants generally contain a halogen (chlorine, bromine, fluorine, etc.) in their molecules • Small molecules which vaporize at relatively low temperatures
Fumigants • Methyl bromide • Dichloropropene • Chloropicrin • Metam-sodium
Transgenic Crops with Insecticidal Properties • Plants genetically engineered to enhance insecticidal properties
Pheromones • Pheromones(chemical used for communication within species) • Chemical signal that triggers a natural response in another member of the same speciesBehavioral chemicals = semiochemicals • Sex Pheromones • Are released by either one( mainly the female) or both genders for the purpose of mate attraction • Aggregation pheromones • Function in defense against predator, mate selection and overcoming host resistance by mass attack • Alarm phrmones • Some species release a volatile substance when attacked by predator that can trigger flight ( in aphid)
Pheromones • Trail pheromones • Are common in social, for example ants make their paths with these pheromones which are non volatile hydrocarbones • Releaser pheromones • Are powerfull attraction molecules that some insects may use to attract males from a distance of two miles or more
Pheromones • بدا المختصون في استخدام الفرمونات و خاصة الجنسية منها للحد من اضرار الحشرات حيث تم انتاج مركبات شبيهة بالفرمونات و قد نجحت بعض التطبيقات الحقلية باستخدام الفرمونات المصنعة للتقليل من اضرار بعض الحشرات كدودة جوز القطن القرنفلية و يمكن استخدام الفرمونات المصنعة او الطبية في مقاومة الحشرات بتوجيه افراد الافات الى مصائد تحتوي على مواد سامة.