Insects fitness resistant

Such a strong impact on survivorship or fecundity, and on the fitness of individuals, means exerting strong natural selection on herbivorous insects. This should favor the rapid evolution of insect adaptations which overcome it. This is, of course, a common occurrence in the application of pesticides or the development of resistant crop plant cultivars (11). The supposition that plant defenses select for detoxication adaptations in insects is the foundation of the concept of coevolution (12). 

Although a toxic plant chemical may not fit either category perfectly, those chemicals discussed below that are tissue specific would generally be considered to show specific resistance. It Is interesting to note that those phytochemicals that are especially toxic to one group of Insects are quite often essential dietary Ingredients or feeding stimulants to other Insects that feed primarily on that plant. 

In Culex, for example, the overproduced esterase amounts to 6%-12% of the total protein of the insect (24.) and in the aphid 3% (12) This is a large diversion of resources into production of an enzyme that is apparently of little or no use in the absence of insecticide, but its consequences to the insect in terms of "fitness" are not yet adequately known. In Culex, resistance in newly colonized field strains is moderately unstable, but becomes relatively stable after prolonged rearing of the strain under insecticidal selection in the laboratory. 

Few studies have been undertaken of the energetic cost of resistance, the resistance mechanism is often not specified in these studies, and the parameters chosen for measurements vary between studies. Comprehensive information is therefore not available. Still, this kind of information is important for understanding the evolution of resistance and its stability. Most new insecticides, it appears, have a mode of action identical to or extremely similar to one that was used previously. The successful use of new insecticides therefore depends on what kinds and frequencies of resistance genes are already present in insect populations to be controlled. It can be expected that resistance mechanisms that affect fitness will be less stable than those that do not. There is, thus, a need for more studies of the relationships between resistance mechanisms and biotic potential in insects. 

Note The enzyme of resistant insects is a little less efficient by having a slightly higher Km value. This indicates a somewhat less efficient enzyme, but the difference is so slight that it does not cause any reduced fitness for insects because the amount of and activity of acetylcholinesterase are almost always much higher than strictly necessary. LD50 = lethal dose in 50% of the population. Vm = maximum enzyme velocity. 

Studies of the potential costs associated with xenobiotic resistance in the absence of the selective agent can suffer from several confounding experimental factors. First, fitness costs associated with strains in which resistance has been repeatedly selected for in the laboratory are unlikely to represent fitness costs associated with resistance mechanisms found in the field. Second, the resistant and susceptible strains compared are also often genetically unrelated and any observed costs may therefore be independent of the resistance trait itself Third, when insects are used they are often not checked for the presence of microbial pathogens, such as Wolhachia, which can influence the outcome of crosses between infected and uninfected strains. 

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