Dosing leaves with Zinc Nitrate for pollution experiment - Need specific concentration
It seems to me that it will be difficult to get a uniform concentration of Zn in a non-uniform material like dried leaves, unless you measure only in bulk (this pile of dried leaves weighs X grams and contains 2000X micrograms of Zn). Things get more confusing if the insects don't eat all the dried-leaf structure (leaving stems, for example).

I'm also not sure how you'll get all the zinc from 1 ml of liquid onto a 0.1g leaf sample. (And, of course, the leaf won't be dry for a while after that!) I think a more concentrated solution would make your task easier. Your math for adjusting the concentration to match the amount of leaf matter appears correct.

As an aside, is your question confusing LD50 (micrograms per gram of insect) with leaf concentration (micrograms per gram of leaf)? I'm not sure why the concentration in the leaves would need to correspond to the LD50, unless there's something significant about the insects eating their own body weight in dried leaves...?