There's no mistaking the toll of voracious roseslugs. Shiny new leaves are perforated with holes or stripped of green leaving behind a lacy brown skeleton. The culprit actually isn't a slug, but the larvae of sawflies, tiny wasps. Sawflies lay eggs on the underside of leaves and when they hatch, the larvae feed there. At the first sign of damage inspect leaves for the light green caterpillar-like larvae about 1/2-inch long. For minor infestations caught early, remove affected leaves and crush any larvae. Larger numbers can be treated with strong sprays of water to the underside of leaves or a coating of horticultural oil, neem oil or insecticidal soap. None of these treatments harms bees or other beneficial insects. Because this is not a caterpillar, Bt (Bacillus thuringiensis) is not effective.