An insect called the hemlock woolly adelgid was introduced to a virginia forest ecosystem. this pest feeds on the nutrients stored inside a hemlock tree, resulting in the death of the tree. which kind of data would best a student evaluate the effect of this insect?

Evaluation of hemlock tree will be helpful in this case. The student should get a data on the number of hemlock trees that have died in the past few years. Further, biochemical evaluation of the tree will show the presence/absence of the nutrients which are used by the insects. The absence of these compounds will indicate the action of the insects. 
Another measure is the evaluation of the adelgid population which have grown over the time, compare it with the native species.