Check plants regularly between late April and October for the presence of larvae. Hand removal may not be possible due to the spines on the stems of a berberis.
If a plant is repeatedly attacked consider replacement it with a non-susceptible alternative.
The larvae can be controlled by spraying the shrub with pyrethrum (e.g. Py Spray Garden Insect Killer, Bug Clear Gun for Fruit and Veg, Defenders Bug Killer or Growing Success Fruit & Veg Bug Killer), deltamethrin (e.g. Bayer Sprayday Greenfly Killer) or lambda-cyhalothrin (Westland Resolva Bug Killer).
Do not spray plants while they are in flower due to the danger to pollinating insects.
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)