Roseslug sawflies are wasps with an immature stage that feeds on the underside of rose leaves. The immature insect looks like a caterpillar but is difficult to see because it is greenish-yellow in color. We have three species in the mid-Atlantic, and they are the bristly rose sawfly, the roseslug sawfly, and the curled rose sawfly, which is covered in bristles.

Figure 1: Adult Rose Slug Sawfly; Whitney Cranshaw, Colorado State University

Figure 2: Rose slug larvae; Brian Kunkel, University of Delaware.

Life Cycle

Rose slug sawflies may have one or more generations per year and this is dependent on the species found on the plant. Adults emerge (Fig. 1), mate and lay eggs that hatch after about 10 - 14 days. Larvae (Fig. 2) are often found in late May to early June. The larvae appear in mid to late May and will cause window pane damage to leaves (Fig.3). Eventually, damage to foliage can cause a plant to look poorly; however, the health of the plant is not harmed (Fig. 4). Fully grown larvae drop from the plants in late June to early July to pupate. Pupated sawflies remain in the soil until they either emerge in mid-August to early September or the following spring (species dependent).

Figure 3: Rose slug Sawfly “window pane” damage; Brian Kunkel University of Delaware, bogwood.org

The sawflies may skeletonize leaves when their populations are high, but this leaf damage still does not cause significant damage to the health of the plant.

Figure 4. The overall appearance of rose slug sawflies damage; Tracey Wootten, University of Delaware.

Biological Control

Little information has been documented about the specific natural enemies of roseslug sawflies. Lady beetles, spiders, predatory bugs (e.g., assassin bugs), and lacewings are all possible generalist predators that would eat this soft-bodied herbivore. Parasitoids may also help keep these insects suppressed.

Treatments

Small populations of sawflies can be managed by hand removal or strong streams of water sprayed to the underside of leaves with a garden hose.

Insecticidal soap or horticultural oil are two products that may give some control of this pest, but direct contact with the insect is needed; consequently, the underside of the leaves must be sprayed. There are other insecticides available for use to manage this pest, and this information can be obtained by contacting your local cooperative extension office for more information.

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