Knockdown resistance

Kneaders Kneading Kneading mixers Knecht compound Knecht method Knife mills Knight and Allen Knives Knize Ten Knockdown Knockdown resistance... 

Mechanism of action can be an important factor determining selectivity. In the extreme case, one group of organisms has a site of action that is not present in another group. Thus, most of the insecticides that are neurotoxic have very little phytotoxicity indeed, some of them (e.g., the OPs dimethoate, disyston, and demeton-5 -methyl) are good systemic insecticides. Most herbicides that act upon photosynthesis (e.g., triaz-ines and substituted ureas) have very low toxicity to animals (Table 2.7). The resistance of certain strains of insects to insecticides is due to their possessing a mutant form of the site of action, which is insensitive to the pesticide. Examples include certain strains of housefly with knockdown resistance (mutant form of Na+ channel that is insensitive to DDT and pyrethroids) and strains of several species of insects that are resistant to OPs because they have mutant forms of acetylcholinesterase. These... 

The mechanisms of resistance fall into two main categories. Many insects produce an increased level of detoxifying enzymes, such as esterases, that modify the insecticides to inactive metabolites very rapidly. Such a system is seen in aphids that are resistant to OP insecticides. In other cases it is the target site that is modified such that the insecticide (the enzyme inhibitor) no longer binds to the target and is, therefore, ineffective. This has recently been shown to occur in some aphids that are resistant to OP insecticides but the classical example is knockdown resistance (kdr) and super-kdr to pyrethroid insecticides shown by many insects but particularly house flies Musca domes tied). This resistance is thought to result from a modification of... 

Soderlund, D.M. and Knipple, D.C., The molecular biology of knockdown resistance to pyrethroid insecticides, Insect Biochem. Molec. Biol., 33,563, 2003. 

Naturally Occurring Point Mutations in the Sodium Channel Gene Responsible for Knockdown Resistance to Pyrethroids. 

This term was originally used to describe the incapacitation of insects such as mosquitoes by insecticides (Asher, K.R., Preferential knockdown action of cetyl bromoacetate for certain laboratory-reared resistant stains of houseflies. Bull. World Health Organ. 18, 615-611, 1958 Cohan, F.M. and Hoffmann A.A., Genetic divergence under uniform selection. II. Different responses to selection for knockdown resistance to ethanol among Drosophila melanogaster populations and their replicate lines. Genetics 114,145-164, 1986 Bloomquist, J.R. and Miller, TA., Sodium channel... 

The target biomolecules for DDT and the pyrethroids are the sodium channels in the axon. One very common type of resistance is the so-called knockdown resistance, or kdr resistance. In this case one or more amino acids have been changed due to point mutation so that DDT or pyrethroids do not bind. Whereas houseflies that are resistant due to the presence of the DDT dehydrochlorinase type of glutathione transferase will be paralyzed by DDT, it is found that when DDT has been detoxicated, the flies wake up and... 

Zlotkin, E., Devonshire, A.L., and Warmke, J.W. 1999. The pharmacological flexibility of the insect voltage gated sodium channel toxicity of AalT to knockdown resistant (kdr) flies. Insect Biochem. Mol. Biol., 29, 849-853. 

Abundant use of one of the most commonly used insecticides in crop protection, pyrethroids, has led to the development of resistance in many insect species.One of the most important mechanisms is that of knockdown resistance (kdr), caused by several mutations in the gene (L1014F and M918T), which confers crossresistance to the entire class of pyrethroids. Another problem is that most insecticides cause toxicity in organisms other than insects because of the general conservation of the voltage-gated Na" " channel structure... 

Ingles, RJ., Adams, RM., BCnipple, D.C., and Soderlund, D.M. 1996. Characterization of voltage-sensitive sodium channel gene coding sequences from insecticide-susceptible and knockdown-resistant house fly strains. Insect Biochem. Mol. Biol, 26, 319. 

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