Disclaimer - I am not trying to argue, just starting a discussion
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Parasitologists continually lamented the impact that infrequent treatment with parasisticides has on the insect population and the continued efficacy of the parasiticides
Poor management of ANY pesticide will result in resistant populations and/or continued exposure (even at recommended dosage and frequent applications) of the same class of pesticide (same mode of action) will result in resistant populations
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When first applied in adequate dose the parasiticide (Permethrin, in this case) is effective at killing the bugs. ALL of them.
Is the Permethrin "killing" the insects? I know it can, but is it? I thought that the treatment acted as a "repellent"???
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On the individual level, it is easy to write this off as not applicable, as the time in a particular area, frequency of exposure, etc are unlikely to be sufficient to have a major impact on the environment. However, in areas where this type of use is common... like, say, shelters along the AT... where consensus has created a consistent and high frequency of useage, it is entirely plausible to see the bug population evolve resistance relatively quickly.
If the treatment is "killing" the insects, then yes, the above statement is applicable...If "repellent", then not (I could be wrong)
I think the biggest problem with resistance comes from when the chemical is applied directly to the environment...i.e. crop protection - where the chemical is broadcast across the field, in order to reduce populations below the economic threshold level. In this scenario, the purpose is to "kill" insects
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In the past this wasn't a problem, as developing new molecules could be done fairly cost effectively. Today, all the easy ones have been used, and development of new molecules is much more difficult, time consuming, and costly. So when the current crop of parasiticides become ineffective, we may be in for a rude awakening.
The "easy" ones, some of the best pesticides are removed from the market due to environmental considerations (not b/c of resistance)...all one has to due is frequently change the chemical class in order to reduce the occurrence of resistance populations, so the efficacy of any particular chemical is not changed
The cost of developing a new chemical, stems from the EPA requirements, which is why "new" pesticides are commonly being developed from "natural" sources (as opposed to synthetic chemicals)...as the EPA requires less stringent testing on so-called "natural" derived chemicals (which is assumed to be better for the environment...and we all know what happens when we assume, IMOHO)
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For a great example, look up the recent and steadily decreasing efficacy of Frontline for treatment of fleas on dogs. As owners try to stretch the duration between applications, fleas are exposed to decreased levels of the parasiticide and some survive... and breed... resulting in more fleas with a higher tolerance for Frontline. Frontline is a great parasiticide, but it has been abused by well meaning folks that didn't understand what they were doing was creating a problem.
In this scenario, Frontline is "killing" the fleas, so resistant populations are being selectively favored
Also, people need to apply at the recommended dosage (do not try to "stretch" the duration between applications) as this will increase the rate at which resistance is acquired, and not provide your pet with adequate protection
This is also true (especially, as bacteria evolve much faster) for taking antibiotics... as we all know, that if you are prescribed 2 weeks medication, then complete the medication cycle (even if you feel better after only a week)
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If reapplied frequently enough that the potency never diminishes enough that mutated/resistant parasites can survive, then this particular problem is solved
You can still develop resistance from continued exposure at recommended potency/dosage/applications...just the rate at which resistance is acquired is lowered (often predicted)
Thank You rjcress for bringing this topic to the forefront of peoples minds...and it makes for a great discussion :D