Description of rose sawfies
There are three main species of roseslug, the bristly roseslug, the roseslug, and the curled roseslug. The two mainly seen in Iowa are the roseslug and bristly roseslug.
The roseslug is a sawfly larva (plant-feeding wasp). They are velvety, yellow-green in color and up to 1/2 inch long. They have a tapered shape and slimy appearance that gives them a vague resemblance to a true slug. Sawfly larvae have jointed legs and a bead-like head. Neither characteristic is present in true slugs (mollusks).
The male bristly roseslug is pale green in color and is covered with many hair-like bristles all over the body. The females are shiny black with yellowish-orange markings on the body.
Life cycle of rose sawfies
The roseslug has one generation per year, with larvae appearing in mid to late spring (May). Fully-grown larvae drop from the plants and burrow into the soil by mid-June. They will remain dormant underground until next spring when the adults emerge and lay eggs on the new rose foliage to begin the cycle over again. Bristly roseslugs may have as many as six generations each year.
Damage caused by rose sawfly larvae
The larvae eat the soft part of leaves leaving behind the network of veins and one epidermis layer. The exposed epidermis quickly turns brown and crisp. Because the veins of the leaf are left intact the damage is called skeletonization (that is, the “skeleton” of the leaf remains). This damage may also be called “window-paning.”
Management of rose sawfies
Larvae that are discovered while they are still small can be effectively controlled with any rose insecticide spray or dust. The key is to find larvae while they are still small and before damage becomes severe. There is no need for control after the larvae have finished eating and left the plants.
When spraying, be sure to spray both sides of the leaf and the ground below the plant as the larvae pupate in the soil prior to overwintering.
Do you live in Iowa and have an insect you would like identified?
The Iowa State University Plant & Insect Diagnostic Clinic will identify your insect, provide information on what it eats, life cycle, and if it is a pest the best ways to manage them. Please see our website for current forms, fees, and instructions on preserving and mailing insects.
Contact information for each states diagnostic laboratory for U.S. residents. If you live outside of Iowa please do not submit a sample without contacting the Plant & Insect Diagnostic Clinic.