Strategies for dealing with box caterpillar

Box tree caterpillar/RHS Gardening
Box Tree Moths ‘plague’ – What to do – (Updated 26/04/18) – EBTS

This pest is ravaging the box plantations of London and the South East, and it's not clear to me whether growing Buxus will remain a realistic proposition. The RHS and the European Boxwood and Topiary Society (in the leaflets linked above) suggest a number of approaches, including using some domestic contact insecticides and one systemic one.

But I don't really see how to make them work in practice if there are several plants or hedges.

The problem is that there are multiple cycles of infestations each year, the caterpillars can destroy the foliage on a plant in a very short time, they hide deep in the plant, hatch out over a long period of time, overwinter, they're camouflaged so hard to spot and they sometimes protect themselves from insecticide with a waxy web.

All the insecticides listen don't remain active for long, and indeed need the spray to touch the caterpillar.

There is a more long lasting insecticide which may be effective, Decis, but the law requires a licence to use it.

Any ideas, anyone?