A Group That Is Experimenting with Selection in an Insect

A group that is experimenting with selection in an insect species due to exposure to a newly developed insecticide,cpd AW143,has found that,after 10 generations of exposure,the population is now bimodal in its response to the drug.Close to 30% of the population are completely normal while 70% live only about 1/6 of the normal lifetime.This is an example of

A) threshold effect.
B) stabilizing selection.
C) additive genes.
D) directional selection.
E) disruptive selection.