Insects resistance development

Second is the resistance problem. To our knowledge there are no examples of synthetic insecticides that have been totally immune from insect resistance development, Should... 

Provides a coordinated crop protection industry response to the development of resistance in insect and mite pests. During the last decade, IRAC has formed several international working gi oups to provide practical solutions to mite and insect resistance problems within major crops and pesticide groups. 

In addition, naturally growing plants resist plant pathogen and Insect attack because resistance develops over time via natural selection (35). Also, most natural and crop plants have, as a part of their basic physical and chemical makeup, a wide array of mechanisms that help them resist pest attack. These Include chemical toxicants, repellents, altered plant nutrients, hairiness, thorns, and diverse combinations of these (35). 

The development of resistant strains of pest species of insects has been intensively studied for sound economic reasons, and there are many good examples. For further information, see Brown (1971), Georghiou and Saito (1983), McCaffery (1998), and Oppenoorth and Welling (1976). Some examples of mechanisms of insect resistance are given in Table 4.3. 

DOWN R E, FORD L, BEDFORD S J, GATEHOUSE L N, NEWELL C, GATHOUSE J A, GATEHOUSE A M (2001) Influence of plant development and environment on transgene expression in potato and consequences for insect resistance. Transgenic Res. 10(3) 223-260. 

The development of resistant strains of an insect to a given insecticide is not new. Melander (7) in 1914 pointed out that the San Jose scale in Washington had developed a resistance to lime-sulfur sprays. Recently Babers (1) of the Bureau of Entomology and Plant Quarantine brought together an excellent evaluation and summary of the literature dealing with the development of insect resistance to insecticides he lists 111 references to work on this phenomenon. 

These synthetic pyrethroids mimic natural counterparts, of which the most important is pyrethrin 1 (10.265). Unfortunately, the natural products lack the photochemical and hydrolytic stability necessary for use as wool insect-resist agents. The synthetic products have the required stability, yet retain the low mammalian toxicity and low environmental retention of the natural products. Permethrin, however, is toxic to aquatic life and is therefore subject to increasingly severe discharge limits. There is some evidence that permethrin is less effective against larvae of a certain beetle. This can be compensated for by using a combination of permethrin with the hexahydropyrimidine derivative 10.264. Some possible alternative pyrethroids have been mentioned [517] as development products (10.266-10.269). 

A development reported recently [519] involves reduction of the cystine disulphide bonds in wool with either thioglycolic acid or tetrakis(hydroxymethyl)phosphonium chloride to form thiol groups, followed by crosslinking with bifunctional reactive dyes. This gave improved insect resistance but had adverse effects on physical properties such as strength, shrinkage and stiffness, thus limiting the potential of the process for commercial use. 

Explanatory knowledge is information that explains why things are so or why certain effects will happen. Here is where it is possible to determine the direction of the solution. Examples the way Bt proteins affect specific pest and beneficial insects what are the main reasons for unwelcome erosion effects mechanisms of vertical gene flow mechanisms of resistance development. 

Insects have acquired resistance to organochlorine compounds, such as DDT and BHC, developed as agricultural and hygienic insecticides after World War II. This insect resistance was also acquired to subsequent organophosphorus compounds and carbamate insecticides. Photostable pyrethroids have been developed for outdoor use because pyrethroids were found to be effective against these resistant pests. As a matter of course, these pyrethroids are also effective against sanitary pests however, problems associated with safety and chemical residues indoors must be resolved. 

Resistance to insecticides has drawn global attention since the Korean War in 1950 when the mass use of organic synthetic insecticides, such as DDT and BHC, against agricultural pests and sanitary pests became common. Organophosphorus compounds and carbamates were used thereafter, but invited problems of safety concerns and insect resistance. Synthetic pyrethroids were watched with keen interest as alternatives and have become used widely not only for sanitary pests but also agricultural pests. The development of resistance to synthetic pyrethroids is also not a rare phenomenon and has spread all over the world. 

Resistance to antibiotics has a close parallel that has become equally familiar over the past fifty years. On repeated exposure, agricultural pests typically become tolerant of a pesticide that is used to control them. Farmers know that the amount of pesticide required to achieve control increases from year to year. Insect pests develop resistance through evolution in the same way that bacteria do. One or two serious pests are now essentially immune to all available pesticides, and many others are moving in that direction. 

A newer class of insecticides is the pyrethroids. These are synthetic derivatives of pyrethrins, which are natural extracts from chrysanthemums. Pyrethroids have been developed to be more stable (and thus more effective as insecticides) than the pyrethrins, which are particularly instable in light. Pyrethroids are frequently used as broad-spectrum insecticides. They have high insect toxicity, but lower mammalian toxicity than their organophosphate or carbamate counterparts. Pyrethroids are still limited in effectiveness due to their environmental lability, their high cost, and their potential for resistance development. 

Insects have developed resistance to cyanide, chlorinated hydrocarbons, organophosfiiates, carbamates, synthetic pyrethroids, and other insecticides ( ). This is not surprising vrtien considering the same complex of detoxifying enzymes, mainly r resented by hydrolytic, conjugative, and oxidative enzymes 9) is capable of detoxifying natural toxins as well as man-made materials. This ability is due to apprcpriate enzymes and/or isozymes that results in broad-substrate capabilities. For insects that feed on a wide variety of hosts (polyphagy), the spectrum of toxins that can be dealt with is truly remarkable. 

The introduction of synthetic pesticides heralded a new era in which agricultural production flourished. However, the use of pesticides introduced unexpected problems. In the case of insecticides, beneficial as well as harmful Insects were killed. Insects rapidly developed resistance to the insecticides, requiring the introduction of new and more potent chemicals. 

Phytoecdysones, due to their effects on the behavior and the development of certain species of Insects, appear to be components of multichemical defensive strategies found In some Insect-resistant plant species ... 

Many new insecticides are rapidly being introduced, but in general they appear to have several serious disadvantages. They are costly and many of them create a health hazard to the operator or the consumer. In addition, insects have developed resistance to certain insecticides. In other cases the use of newer insecticides has been a factor in the outbreak of so-called minor pests. In short, there is little indication that the long-sought cure-all insecticide is in sight. 

Another important problem is the development of insects resistant to insecticides. This often arises as a result of increased levels of carboxylesterases which hydrolyze both organophosphates and car-baryl.h/1 A mutation that changed a single active site glycine to aspartate in a carboxylesterase of a blowfly changed the esterase to an organophosphorus hydrolase which protected the fly against insecticides.)... 

Two problems must be considered. Insects do develop resistance to the Bt toxin.m This problem... 

Earlier work in this field [28] indicated that acetylcholinesterase enzymes would be suitable biomolecules for the purpose of pesticide detection, however, it was found that the sensitivity of the method varied with the type and source of cholinesterase used. Therefore the initial thrust of this work was the development of a range of enzymes via selective mutations of the Drosophila melanogaster acetylcholinesterase Dm. AChE. For example mutations of the (Dm. AChE) were made by site-directed mutagenesis expressed within baculovirus [29]. The acetylcholinesterases were then purified by affinity chromatography [30]. Different strategies were used to obtain these mutants, namely (i) substitution of amino acids at positions found mutated in AChE from insects resistant to insecticide, (ii) mutations of amino acids at positions suggested by 3-D structural analysis of the active site,... 

---