Boxwood leafminer larvae are plump and ready to pupate. My daughter and I found a bunch of larvae in bushes in our neighborhood near NC State. These are easy to find. Boxwood leafminers feed within boxwood leaves causing the leaf to become blistered and a little puffy. Take a leaf that looks blistered and tear it open. You will see the bright orange larvae wriggling around inside.
Last year boxwood leafminer adults emerged on April 15 in Raleigh. At this point, the larvae are not feeding much if at all so systemic insecticides won’t do any good. You can target the adults with a product that contains abamectin, like Avid.
The larvae do not feed much in the summer, but feed heavily in the fall. Thus, a systemic like imidacloprid applied in late summer will kill the larvae as they feed. Larvae also feed heavily in early spring to complete development, so imidacloprid applied in late winter can also kill larvae. Of course, by this point much of the damage is done, but it will reduce adult emergence.
At the end of our walk my daughter and I ripped open a dozen or so leaves and 8-12 larvae wriggled out of each one. We collected all of these larvae in an acorn top just to see how much we could fill it.