(Plant Protection) insecticides
How Do Insecticides Work?
generally target the: 1. Nervous system 2. Growth and development of the Pest 3. Energy production of the Pest.
Improved Usage of Pesticides
• Apply pesticide only when pest is present and is nearing economic or aesthetic thresholds • Apply when pest is most vulnerable, Normally when they are young and immature • Sprayer calibration • Decreased drift • Target spraying and spot treatments • Timing and selection to avoid harming natural enemies • Use attractants to lure pests into a concentrated area
Types of Insecticides
• Four of the more common types of insecticides, based on their structure are: • Chlorinated Hydrocarbons • Organophosphates • Carbamates • Pyrethroids
How are Semiochemicals used?
• Monitoring • Trapping • Disruption of Mating • Diversion • Reduced Feeding
What makes a good insecticide?
• Target pest specificity • Good suppression of target pest • Rapid suppression of target pest • Degrades fairly rapidly - Very important • Low mammalian toxicity • No Phytotxicity • No risk to environment
Toxicity measured by LD50
- Class 1a Extremely Hazardous <5 - Class 1b Highly Hazardous 5-50 - Class 2 Moderately Hazardous 51-500 - Class 3 Slightly Hazardous >501
Insecticides Targeting the Central Nervous System
1. Organophosphate & Carbamates • Cholinesterase inhibitor • Overstimulation of CNS & insect dies 2. Acetylcholine Receptor Stimulatuion • Neonicotinoids • Antagonists of Ach neurotransmitter 3. Organochlorine Insecticides • Effect the chloride channel leading to continuous overstimulation of the CNS and insect death 4. Pyrethrins (Natural) & Pyrethroids (Synthetic) • These are Sodium channel modulators • Act on tiny channels through which sodium moves • Result in continuous excitation of neurons, tremors and death
Systemic insecticide
AI is taken up primarily by the plant roots and leaves, and translocated throughout the plant where it can affect plant feeding pests most effective on insects with piercing or sucking mouthparts • Aphids, Whitefly, Mealy Bugs etc
Semiochemicals
Any type of a chemical used for communication with other insects - Pheromones; Signals emitted and perceived by members of the same species. Many different types of pheromones - Allelochemicals; Signals or toxins emitted and perceived by members of different species. eg; Kairomone - attracts parasites to host
Microbial Insecticides
Bacillus thuringiensis (Bt) Carrier used to spread toxic compounds with kills certain soil pests
Insect Growth Regulators
Chemical compounds that slow down or alter the growth of insects and are normally effective in minute quantities. can effect: Molting - Pest unable to complete life cycle Reproduction - Pest remains juvenile Behaviour - Chitin synthesis
Botanic Insecticides
Derived from plants or plant products - Pyrethrum (Chrysanthemum) - Azadiractins (Seeds of the Neem tree) - Nicotine (Tobacco leaves) - Rotenone (Derris roots)
Types based on origin and MOA
Insect Growth Regulators Semiochemicals Synthetic Insecticides Botanical / Natural Insecticides Oils Microbial Insecticides
Growth & Development
Insecticides targeting growth & development -Chitin Synthesis Inhibitors -Insect Growth Regulators
contact insecticide
Kill pests by direct contact during spray application or by coming in contact with wet residues, usually quick
Horticultural Oils
Refined petroleum products - Phytotoxic therefore need to be highly refined • Divided into: - Summer Oils; Can be applied to trees in full foliage - Dormant Oils; Can be applied to trees when dormant - Tar Oil; often used to kill eggs of mites and aphids and scale insects
Synthetic Insecticides
Stomach Poisons • Fatal only after ingestion by the pest Contact Poisons • Absorbed through body wall Systemic Poisons • Applied to plant and moves within plant - primarily aimed at insects with piercing / sucking mouthparts Fumigants • Contact site is tracheal system • Released in air tight enclosures
The Nervous System
acetylcholine (ACh) and gamma- aminobutyric acid (GABA) are important targets of some insecticides