Knock-down effect

Cross-resistance to pyrethroids for outdoor use has developed markedly in M. domestica, mosquitoes, cockroaches, and so on however, it has also been found that natural pyrethrins as well as d-allethrin and prallethrin (ETOC ), which have very similar chemical structures and the same configuration as natural pyrethrins, show an extremely low degree of cross-resistance development by these highly-resis-tant sanitary pests compared to photostable pyrethroids. Many novel synthetic pyrethroids recently developed as household insecticides have tended to pursue efficacy improvements in terms of rapid knock-down effects, residual efficacy or volatility. 

In the preparation of commercial pesticide formulations, the biochemical and toxic properties undergo phenomenal modifications. These reactions (and the effects thereof) are called synergism, antagonism, and additive effects. In pest control management, different OPs are mixed to achieve quick knock-down effects, and absence of residues effects, for the better killing of crop pests (Table 5-2). 

At 23 °C, antifoam CF and AF 9000 both have a superior knock-down effect, but TP 3860 has the best persistence and best overall antifoam performance. In the series TP 3860/3861/3862, increasing antifoam viscosity decreases knock-down and persistence performance significantly. 

Since the 1920s several research workers have investigated the insecticidal effect of various thiocyanates. The action of these compounds is characterised by the knock-down effect and by the contact character of action. They have therefore mostly been used in combination with other insecticides, such as rotenone, pyrethrum and DDT. From the end of the 1940s onwards their use was gradually discontinued, due mainly to their disagreeable odour and their phytotoxic and skin-irritating properties. 

If we consider that insecticide repellency, mentioned in early studies, is not a typically sublethal effect, the hrst report of a consequence of low doses of insecticide on non-Apis bees appeared in 1981 [23]. The authors, comparing two pyrethroids and organophosphates on the leafcutting bee in laboratory tests, found that a high percentage of comatose bees recovered. This was observed only with the pyrethroids fenvalerate and decamethrin (deltamethrin) which caused a strong knock-down effect within the hrst hour after application. 

Figure 7.1 Mortality rate and knock-down effect of four insecticides against Megachile rotundata males exposed to residues on paper (after Tasei and Dinet, 1981) [23].

One hour following a fenvalerate spray at 50g/ha, more than 80 percent of M. rotundata males were knocked down and counted dead, but 62 percent of the treated population recovered within 14 hours. This was not the case for males sprayed with deltamethrin at 7.5g/ha which were all killed. When males were maintained on dry residues of both compounds, the knock-down effect was also observed and recovery affected 44 and 59 percent of males treated with deltamethrin and fenvalerate, respectively [23]. 

The instantaneous destruction of polyhedral foam is called knock-down effect by some authors. 

Non-emulsifiable Excellent efficacy and long term persistence Needs shear for incorporation, poor knock-down effect, limited compatibility... 

All six compounds are colorless liquids, soluble in alcohol, petroleum ether, and tetrachloromethane, they are easily oxidized and rapidly lose their activity in light and air and are also sensitive towards moisture and alkali. They are contact poisons that rapidly enter the nervous system and induce the characteristic symptoms in insects (high excitation, followed by impairments of coordination, paralysis, and finally death). The first effect starts rapidly, i.e., the insect is unable to move within a few minutes. This knock-down effect, especially in flies, is only achieved by a few insecticides. However, the dose required for this effect is usually not sufficient to cause death since the active principles of P. undergo rapid detoxification by enzymatic oxidation in the insects, thus some of the afflicted insects can recover. This can be prevented by the addition of synergists or active principles of the phosphoric acid ester and carbamate type. R, especially under the recommended conditions of use, is relatively harmless for humans and warm-blooded animals (birds, mammals). The synthetic pyrethroids, devel-... 

Tests also continued with TL2833, a short-acting oripavine derivative which has a rapid knock down effect when injected subcutaneously. Although it is not entirely clear whether this effect had first been observed in animal studies, there is some evidence to suggest that humans were involved in the testing of the substance from early on. In March 1964, one... 

The six pyrethrins, Pyrethrin I, Jasmohn I, Cinerin I, Pyrethrin II, Jas-molin II, and Cinerin II were found to be present in the leaf extract of the Chrysanthemum cinerariaefolium seedlings. Pyrethrins are thought to act as defense mechanisms that prevent insects from feeding on the plant [27]. The pyrethrins repel insects and also paralyze flying insects, thereby exhibiting a knock-down effect. The active components occur to a small extent in all parts of the plant, but especially in the flower heads [28]. 

The change in the alcohol moiety to allethrone led to the development of the first synthetic pyrethroid, allethrin. It also led to improved chemical stability of the natural pyrethrins and to reduced cost, because the original pyrethrins had been sourced from natural products (LaForge and Soloway 1947). The stability of alle-thrin made it superior to the natural pyrethrins in both kill and knock-down effects against mosquitoes. Allethrin s successful discovery was followed by the development of other successful pyrethroids, to wit, tetramethrin (Kato et al. 1965) (1965, patent appl date) from tetrahydrophtalimide, resmethrin (Elliott et al. 1967) (1967, patent appl date) from 5-benzyl-3-furylmethyl alcohol and phenothrin (Fujimoto et al. 1973) (1968, patent appl date) by changing a-benzylfuran to phenoxyphenyl. 

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