Non chemical control
Remove damaged leaves and larvae when you see them.
Leaf-mining insects are difficult to control as the pest is concealed inside the leaves.
Systemic insecticides are absorbed into plant tissues and may control the larvae, but because of the thick cuticle on Sempervivum leaves, uptake may be poor if applied as a foliar spray.
A better means of control would be to use a systemic vine weevil pesticide such as thiacloprid (e.g. Provado Vine Weevil Killer 2) or acetamiprid (e.g. Bug Clear Ultra Vine Weevil Killer). These are watered into the potting compost, where they are absorbed by the roots and taken up into the foliage. In addition to protection against leaf miner, these pesticides will also protect against vine weevil grubs.
When the leaf miner has been a problem, treat container-grown plants in mid-May and early August.
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)