Scientists have studied a population of beetles that have been exposed to a pesticide. some beetles survive by have enzymes that break down the toxin. this trait is passed to their offspring and overtime, the amount of pesticide needed to kill the beetles has increased. what type of selection is the application of pesticides?

Natural selection is the application of pesticides.

Explanation:

Natural selection is a process which is non- random in which a trait increase or decrease in a population due to difference in the survival rate of a population that have that trait. So natural selection helps in the evolution of a population which is more adaptable.

Therefore when a pesticide is used against beetle many of the beetle die due to the pesticide but some beetles survived because they were having a gene that code for an enzyme that breaks down the toxin of pesticide which survived.  

So nature selected those individuals who have genes that allow them to survive in changing and adverse conditions. So these selected individuals will reproduce and pass their genes to their offspring and increase in number.  

Therefore by natural selection, more pesticide-resistant beetle will be produced and so more amount of pesticide should be needed to kill the beetles.

the sphincter muscles at the end of the digestive tract is the anus.