Insecticide Penetration Flashcards
Which three types of transport involve movement down a concentration gradient?
- Facilitated diffusion
- Passive diffusion
- Filtration
What makes mammalian skin a better barrier against contact insecticides than insects?
Mammals have soft, flexible keratinized skin
The outermost layer of the insect integument is _____________
waxy and lipophilic, making it hydrophobic.
Most insecticides are what?
Contact poison
The efficacy of insecticides is highest for what type of compounds?
Non-polar lipophilic compounds
Why is passive diffusion the most common type of movement of insecticides through biological membranes?
because of the lipophilic nature of insecticides and biological membranes
The integument is made up of…
Epidermis and cuticle
What four factors affect the penetration of insecticides?
- Integument thickness
- Lipid solubility of the insecticide
- Solubility of the insecticide in hemolymph
- The types of cuticular components
What three considerations are important for a toxic response to occur?
- Duration of exposure
- Movement across biological membranes
- The toxicant must reach the target site in a sufficient quantity
Why more than 99% of the applied active ingredient does not reach the target site?
Processes including penetration, and transport across membranes, among others, contribute to this inefficiency. However, the ability of insects to metabolize toxic foreign compounds might be the single most important factor.
What is detoxification?
Detoxification is the ability of insects to convert toxic compounds into non-toxic substances. However, insects do not always detoxify compounds. Often, insects increase the water solubility of toxic compounds so they can be more excretable, which is not necessarily detoxification.
What do monooxygenases do?
Monooxygenases insert a single oxygen atom from O2 into xenobiotic molecules.
What are Cytochrome P450s?
- Carbon-monoxide-binding pigments of microsomes
- Hemoproteins
What are microsomes?
Microsomes refer to the subcellular fraction containing membrane bound enzymes which are imbedded in the endoplasmic reticulum.
What do hydrolases yield when they split ester compounds by the addition of water?
- Alcohol
- Acid
How do many metabolic reactions alter foreign compounds?
They increase the water solubility of foreign compounds so they can be excreted.
Where is cytochrome P450 typically most concentrated in insects?
The digestive tract
Many metabolic reactions involve formation of a product that is more toxic than its parent compound. What is this phenomenon called?
Activation
What is the primary enzyme system involved in the metabolism of lipophilic xenobiotics in insects?
Cytochrome P450-dependent microsomal monooxygenases
Where is the P450 system embedded in the cell?
Endoplasmic reticulum
