DS - Insecticides II

Question 1

What are the main insect orders? (4)

Answer 1

• Coleoptera
• Diptera
• Hymenoptera
• Lepidoptera

81% of described species come from these orders

Question 2

What are some features of insect diversity? (4)

Answer 2

• Tremendous range of form and function
• Life cycles
• functional feeding traits
• Ubiquitous distribution in terrestrial and freshwater habitats

Question 3

How can insecticides be grouped? (3)

Answer 3

• Chemical structure “class”
• Target site
• Mode of action

Question 4

What are the ways insecticides can act at a target site? (4)

Answer 4

• Modulation
• Excitation
• Blockage
• Inhibition

Question 5

What are the two broad types of insecticide action?

Answer 5

• Insecticides that target the nervous system (5 classes)
• Insecticides that do not target the nervous system (2 classes)

Question 6

How is insecticide toxicity measured?

Answer 6

LD50 (Lethal dose to 50% of the test population)

Question 7

What are some neurotoxic insecticides? (5)

Answer 7

• Organochlorines
• Pyrethroids
• Phenylpyrazoles
• Neonicotinoids
• Organophosphates

Question 8

Give an example of an Organochlorine insecticide

Answer 8

Dichlorodiphenyltrichloroethane (DDT)

Question 9

What are the characteristics of DDT? (5)

Answer 9

• Stable and lipophilic
• Synthesized in 1873, used starting in 1939
• Target site: Sodium channels
• Action: Modulates sodium channels, leading to sustained activation
• LD50: 250 mg/kg (rat)

Question 10

How does DDT affect sodium channels and the nervous system? (3)

Answer 10

• Modulates voltage-gated sodium channels
• Causes negative after potentials
• Leads to repetitive spiking from a single stimulus, resulting in CNS hyperactivity

Question 11

What are the characteristics of Pyrethroids? (5)

Answer 11

• Target site: Sodium channel modulator
• LD50: 1500 mg/kg (rat)
• Type 1: Causes repetitive discharge
• Type 2: Causes no repetitive discharge (slower after potential)
• More stable in mammals, safer for humans than DDT

Less stable than DDT: can be metabolised easier by mammals (safer for humans)

Question 12

What are the characteristics of Phenylpyrazoles? (3)

Answer 12

• Target site: GABA- and Glutamate-gated chloride channels
• Mode of action: Blocks transmitter binding to chloride channels
• Result: Loss of post-synaptic inhibition leading to CNS hyperexcitation

Example: Fipronil reduces chloride ion flow, affecting action potentials

Question 13

What are the characteristics of Neonicotinoids? (4)

Answer 13

• Nicotine-based insecticide
• Target site: Acetylcholine receptors (mimics Ach)
• Mode of action: Nicotinic acetylcholine receptor agonist
• Result: Sustained neuron excitation (acetylcholinesterase does not break it down)

Question 14

What are the characteristics of Organophosphates? (6)

Answer 14

• Derivatives of phosphoric acid
• Oxygen can be replaced by S, C and N to yeild different derivatives
• Target site: Acetylcholinesterase (AChE)
• Action: Inhibits AChE through phosphorylation (dephosphorylation through hydrolysis)
• Result: Sustained acetylcholine at synapse, leading to excess neuroexcitation
• Classed as irreversible inhibitors

Question 15

What are some non-neurotoxic insecticides? (4)

Answer 15

Insect growth regulators (IGRs)
Calcium channels (muscle)
Cuticle dehydrators
Energy production inhibitors

Question 16

What are the features of Insect Growth Regulators (IGRs)? (4)

Answer 16

Example: Methoprene, a Juvenile Hormone (JH) mimic
* Causes early moulting
* early nymphal mounting
* sterilization
* deformed wings (morphogenic malformation)

Question 17

What are the features of Cuticle dehydrators? (2)

Answer 17

• Example: Diatomaceous earth (fossilized diatoms)
• Disrupts lipids in the cuticle, removing waterproofing