Knockdowns

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

DEET-treated net jackets also provide good protection, but an additional appHcation of 10—25% solutions of repellent to the unprotected face is necessary for maximum protection. Clothing treated with permethrin [52645-53-1] (9) does not provide the protection expected against these insects. Because sandfly behavior and resistance to quick knockdown are responsible for the numbers of bites recorded, maximum protection from bites thus requires appHcation of DEET or another suitable repellent to the exposed skin when wearing permethrin-treated clothing (35). 

The exhaust gases are generally discharged into dust and fume knockdown equipment to avoid contamination of the atmosphere. Gas-cleaning equipment includes cyclones, setthng chambers, scrubbing towers, and electrical precipitators. Heat-recoveiy devices are utilized both within and outside the lain. These result in an increase in lain capacity or a decrease in fuel consumption. Waste-heat boilers, grates, coil systems, and chains are used for this purpose. 

Dry chemical extinguishing systems-This is used primarily for flammable liquid fires since they provide a rapid flame knockdown and e.xtinguishment. 

The edible parts of parsnips (Pastimea sativa L.), which have been consumed for centuries by humans without causing any obvious harm, were found to contain a chemical of insecticidal and strong synergistic nature (1). The insecticidal constituent, present at about 200 p.p.m., was isolated and identified as 5-allyl-l-methoxy-2, 3-methylenedioxybenzene or myristicin. Its toxicity to various insects [vinegar flies, houseflies, Mediterranean fruit flies, mosquito larvae, Mexican bean beetles, and pea aphids] was established and compared with pyrethrum and aldrin (Tables I and II). The knockdown effect, although definite, was not as great as that of pyrethrum. In tests... 

Sawicki and Elliott (31) re-examined the insecticidal activity of pyrethrin extracts and its four insecticidal constituents against four strains of houseflies, and checked the relative toxicity of pyrethrins I and II. This work confirmed the earlier results, showing that pyrethrin II was 1.3 to 1.6 times more toxic than pyrethrin I, but that the relative toxicities of pyrethrins I and II against the four strains of flies differed little. Resistance to knockdown but not to killing was associated in these strains with resistance to organophos-phorus and chlorinated insecticides. 

Hurst (19) discusses the similarity in action of the pyrethrins and of DDT as indicated by a dispersant action on the lipids of insect cuticle and internal tissue. He has developed an elaborate theory of contact insecticidal action but provides no experimental data. Hurst believes that the susceptibility to insecticides depends partially on the cuticular permeability, but more fundamentally on the effects on internal tissue receptors which control oxidative metabolism or oxidative enzyme systems. The access of pyrethrins to insects, for example, is facilitated by adsorption and storage in the lipophilic layers of the epicuticle. The epicuticle is to be regarded as a lipoprotein mosaic consisting of alternating patches of lipid and protein receptors which are sites of oxidase activity. Such a condition exists in both the hydrophilic type of cuticle found in larvae of Calliphora and Phormia and in the waxy cuticle of Tenebrio larvae. Hurst explains pyrethrinization as a preliminary narcosis or knockdown phase in which oxidase action is blocked by adsorption of the insecticide on the lipoprotein tissue components, followed by death when further dispersant action of the insecticide results in an irreversible increase in the phenoloxidase activity as a result of the displacement of protective lipids. This increase in phenoloxidase activity is accompanied by the accumulation of toxic quinoid metabolites in the blood and tissues—for example, O-quinones which would block substrate access to normal enzyme systems. The varying degrees of susceptibility shown by different insect species to an insecticide may be explainable not only in terms of differences in cuticle make-up but also as internal factors associated with the stability of oxidase systems. 

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... 

Fenpyroximate exhibits acaricidal and knockdown activities on phytophagous mites, such as Tetranychus urticae Koch (two-spotted spider mite) and Panony-chus citrP in citrus, apple, pear, peach, grape, etc. Fenpyroximate inhibits the mitochondrial NADH-Co Q reductase, which induces a decrease in ATP content and morphological changes in mitochondria and ultimately shows the acaricidal and knockdown activities. ... 

Rapid knockdown action toward insects with minimum recovery... 

Table VI. Comparative Knockdown Rate and Power of a Series of Org a nofluorine...

Compound Insect Dosage Knockdown, Hours % Knock down Reference... 

DDT required 8 hours to give same knockdown. o DDT required 24 hours to give same knockdown. h Chlorine analogs required 24 hours to give 50% knockdown. 

Table VI. The knockdown power of the organofluorine insecticides has been determined principally against members of the Diptera order and by a limited number of workers. There is general agreement that DFDT acts more rapidly than DDT, at least against those species with which they have been compared. Prill 92) found that twice the amount of DFDT compared to DDT was required to give the same knockdown against houseflies when tested by a space spray technique with added pyrethrins. The forced contact method of Fay and Buckner 27) revealed that without added pyrethrins DFDT was a more powerful knockdown agent than DDT.

The dehydrohalogenation of DFDT materially reduced its knockdown rate, but the resulting p,p -difluorodiphenyldichloroethylene derivative is more rapid in action than the analogous trichloropropylene compound. The fact that the propylene compound maintained some activity suggests that its increased weight might explain the difference in activity. 

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