Pesticides help!?

Question

explain the mechanism of natural selection and relate it to what happens when insects develop resistance to pesticides.

Answer 1

Great question!  Natural selection depends on a finite rate of mutation to constantly introduce new genetic material into the species.  Most of these random mutations will be neutral or harmful.  But, occasionally a mutation will occur that renders the individual or small group of individuals better fit to contend with their environment.  These individuals will tend to survive longer and produce more offspring.  Hence, the new traits are "selected" by nature.

The same thing happens with pesticide resistance.  A pesticide typically works by blocking a certain essential enzyme reaction in the target species.  In other words, we say that the enzyme is "inhibited" by the active ingredient in the pesticide.  Now, enzymes are proteins encoded by genes (DNA).  Over time a mutation will occur in this gene making the enzyme less sensitive or insensitive to the inhibitor (pesticide).  Those individuals carrying this mutation will fluorish rendering the pesticide ineffective.  Almost every pesticide and herbicide on the market encounters this problem eventually.   That is why companies have to continually come up with new products, to keep ahead of the resistance problem.