AgileGSD
Posted : 4/6/2010 9:09:22 AM
calliecritturs
Rott-n-GSDs
It seems parasites eventually get immune to dewormers if they are overused. For example, in my area botflies are becoming immune to Ivermectin because it is the most used (and least expensive) wormer ingredient on the market for horses.
It's not fequency of use -- it's whether or not the parasite SURVIVES the med. If a too-small dose is given (or if the quality is low) and the parasite "survives" the drug, then the next time the parasite is confronted with THAT drug it has the ability to "survive" it again.
Actually it is frequent exposure of the same pesticide over time that leds to genetic selection for resistance.
"Pesticide resistance is the adaptation of pest species targeted by a pesticide resulting in decreased susceptibility to that chemical. In other words, pests develop a resistance to a chemical through selection; after they are exposed to a pesticide for a prolonged period it no longer kills them as effectively. The most resistant organisms are the ones to survive and pass on their genetic traits to their offspring.[1]" http://en.wikipedia.org/wiki/Pesticide_resistance
"Repeated use of the same class of pesticides to control a pest can cause undesirable changes in the gene pool of a pest leading to another form of artificial selection, pesticide resistance. When a pesticide is first used, a small proportion of the pest population may survive exposure to the material due to their distinct genetic makeup. These individuals pass along the genes for resistance to the next generation. Subsequent uses of the pesticide increase the proportion of less-susceptible individuals in the population. Through this process of selection, the population gradually develops resistance to the pesticide. Worldwide, more than 500 species of insects, mites, and spiders have developed some level of pesticide resistance." http://www.grapes.msu.edu/pesticideResist.htm
"Resistance usually develops by genetic mutation and selection. Types of mutations can include: a change in processes in the pest that make the pesticide harmless, a change in the place where the pesticide enters the pest so it cannot enter, or a change in the behavior of the pest so that it avoids the pesticide. Resistant pests are selected when the pests reproduce. For example, in any pest population there may be some pests that will not be killed by the pesticide. When the pests that survive breed, some of their young will inherit the pesticide resistance. These pests will not be affected the next time the pesticide is used. With each generation, the pest population becomes more difficult to control with the same pesticide. If the same pesticide is applied often, there will be more resistant pests than susceptible pests." http://www.agf.gov.bc.ca/pesticides/a_4.htm
"Pesticide resistance develops when pesticides are used too often and when the same pesticide or similar pesticides are used over and over again." http://www.agf.gov.bc.ca/pesticides/a_4.htm
"It's a huge problem, but the pests are only following the rules of evolution: the best-adapted survive. Every time chemicals are sprayed on a lawn to kill weeds or ants for example, a few naturally resistant members of the targeted population survive and create a new generation of pests that are poison-resistant. That generation breeds another more-resistant generation; eventually, the pesticide may be rendered ineffective or even kill other wildlife or the very grass it was designed to protect.
In many ways, human actions are hastening pests' evolution of resistance. Farmers spray higher doses of pesticide if the traditional dose doesn't kill, so genetic mechanisms that enable the pests to survive the stronger doses rapidly become widespread as the offspring of resistant individuals come to dominate the population." http://www.pbs.org/wgbh/evolution/library/10/1/l_101_02.html
A related note:
"Scientists have raised concerns following the discovery of a single gene that gives vinegar flies resistance to a wide range of pesticides, including the banned DDT.
"This is a warning that we may need to rethink our overall strategies to control insect pests," says University of Melbourne geneticist, Dr Phil Batterham, and Program Leader for the Chemical Stress Program within CESAR, a special research centre that includes researchers from the Universities of Melbourne, La Trobe and Monash.
"The fact that a single mutation can confer resistance to DDT and a range of unrelated pesticides, even to those the species has never encountered, reveals new risks and costs to the chemical control of pest insects. Unless we reassess our current methods of pest management, our future options for control may become severely restricted," he says." http://uninews.unimelb.edu.au/view.php?articleID=198