Answer:
Variation of mouth parts will decrease
Step-by-step explanation:
It is given that the insect population has wide variation in shape of nectar gathering mouth parts. Without any disturbance this variation would continue to exist and would be passed on to subsequent generations.
Now the flower shape has changed which leads to efficient collection of nectar by shorter, thicker mouth parts. Insects with such mouth parts would be more competent than others and hence would thrive in population. They will pass on these traits to the next generations too and ultimately shorter, thicker mouth parts would be preferred over other types of mouth parts which will reduce the variation in population. However the variation would not completely cease to exist.