What´s Insecticide Resistance

Insecticide resistance is defined as a genetically-based decrease in susceptibility of an insect population over time, in response to long-term exposure to an insecticide. There is a shift in the genetics of a population that allows individuals within a previously susceptible population to survive. Resistant populations inherit traits that reduce their susceptibility to individual insecticide. In other words, pests develop a resistance to a chemical through natural selection: the most resistant organisms are the ones to survive and pass on their genetic traits to their offspring (Miller, 2004).Resistance develops in all agricultural insects and they resistant individuals are initially quite rare in pest populations.

The development of resistance in the fields is influenced by various factors. These include biological, genetic Biological factors are generation time, number of offspring per generation and migration. Genetic factors are frequency and dominance of the resistance gene, fitness of resistance genotype and number of different resistance alleles. Genetics and intensive application of insecticides are two factors of several responsible for the development of insecticide resistance. Insects with genes that confer resistance to a particular insecticide or class of insecticides survive treatment and are thereby “selected” to pass on this resistance to later generations. In a population of insects there may be a few individuals that carry the genes for resistance. These genes arise from mutations and are rare. In the natural environment the mutant insect is typically compromised, weaker and produces less progenies. Upon exposure to insecticides, insects that do not carry the resistance genes die, thus allowing the individuals...

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...istance by assessing their mortality after exposure to a range of doses of insecticide and the results compared with those from standard susceptible populations. According to Yu and Nguyen (1992) another method is to use biochemical detection assays to establish the resistance by measuring changes in resistance gene frequencies in field populations under different selection pressures. Much effort has been expended on determining the biochemical or physiological changes underlying Bt resistance. It has been established that the diamondback moth reduced toxin binding to the midgut epithelium as an important resistance mechanism (Perez and Shelton, 1996).

Immunological method is also available but only for specific elevated esterases in collaboration with laboratories that access to the antiserum. There are no monoclonal antibodies, as yet, available for this purpose.