"Dick,  is there any mechanism for determining this level???"

Yes.  The problem is it requires a lot of knowledge about details of metabolic pathways and overall biochemistry as well as responses to varied doses of the pesticide and resistance mechanisms.  You generally are not going to know all the stuff you need to know until resistance happens.  

Let me give one simplistic example.  Suppose resistance is due to one single mutation and that mutation is genetically recessive.  If that recessive mutant exists at a concentration of 10% in some population that means 1% of the population is homozygous for the mutant.  If you kill 99% (all the 90% that does not carry the mutation, plus another 9% that are heterozygous for the mutant) in the very next generation 100% will be homozygous and you get zero control.  But, take the above case and you kill only 90% of the population leaving 10% alive.  One in ten of those left alive are alive because they are homozygous for the mutant.  The other 9% are mainly wild type and 0.9% are expected to be hetero for the mutant.  This is the population that will reproduce and make the next generation.  So, most of the next generation are still going to be susceptible to the pesticide. This assumes cross pollination if the pest is a weed of course.  This points out you must consider the reproductive methods of the target also in doing an optimum kill ratio estimate.  With a kill rate a bit less than 90% in this example you could go until some other mutant happens and still maintain control if you can stand an 85% kill without excessive economic impact on yields.

But, until resistance happens you have no idea how that resistance will be inherited so you can not make any prediction on optimum kill rates.

A short course of antibiotics is a resistance problem because you have not given your bodies immune system enough time to gear up and do its job.  So any somewhat resistant bacteria have been selected and if transmitted the next person may be in real trouble.  If the doctor says ten days treatment he says it for a reason. That reason is it can take that long for your immune system to clean up the remaining bacteria.  You might feel great after 48 hours of taking the antibiotic and feel you do not need to take it the other eight days.  I have had exactly that experience myself.  Stopping soon is dumb and sets the stage for resistance to develop from the remaining bacteria.  Your doctor had a reason based on clinical trials for telling you to take it ten days.  The reason is it takes that long for the bacteria to be totally wiped out by a combination of the antibiotic plus your bodies immune system.

Dick


" Any discovery made by the human mind can be explained in its essentials to the curious learner."  Professor Benjamin Schumacher talking about teaching quantum mechanics to non scientists.   "For every complex problem there is a solution which is simple, neat and wrong."  H. L. Mencken

             ***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software.  For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html