Rose sawflies (roseslugs)—Allantus cinctus, Cladius difformis, and Endelomyia aethiops
At least three species of sawflies (Tenthredinidae) are occasional pests of roses in California. The most common is bristly roseslug (Cladius difformis). Occasional pests are the curled rose sawfly, or curled roseslug (Allantus cinctus), and the roseslug (Endelomyia aethiops), also called American, European, or common roseslug.
Adults are stout, 3/8 to 2/3 inch long, and mostly black with orange or yellow, varying by gender and species. Adults have two pairs of wings with distinct veins and a broad waist, unlike most wasps (Hymenoptera) that have a narrow constriction between the abdomen and thorax.
Larvae have pairs of prolegs (fleshy stubs, or leglike appendages) on at least six abdominal segments; unlike the five or fewer abdominal segments with prolegs on most other caterpillarlike larvae that occur openly on foliage.
Take care to distinguish roseslugs from beneficial syrphid larvae that feed on rose aphids. Roseslugs occur near chewed or scraped leaves, while syrphids occur among aphids and do not chew on plants. Syrphid larvae have no true legs, while roseslugs have three pairs of short legs on the thorax.
Bristly roseslug. Bristly roseslug in California occurs mainly in cooler areas, such as near the coast. Larvae are pale green or yellowish green with a brown head. They grow to about 3/4 inch long and have many, tiny, hairlike bristles. Young larvae chew off the surface of the underside of leaves, leaving windowpanelike damage. Older larvae chew holes through leaves.
Curled rose sawfly. Larvae are green with rows of pale, short, stout projections (tubercles). The head is pale brown to yellowish with a black eye spot on each side. The larvae grow up to 3/4 inch long and often coil their bodies while feeding. They mostly chew entirely through leaves along the edges, leaving mostly veins. They may chew half-moon-shaped cuts in leaf edges that resemble the foliage clipping by leafcutting bees. At maturity, larvae of curled rose sawfly chew into stems and form a pupation chamber in pith.
Roseslug. Larvae are mostly green on top and yellowish along their sides. They have a brown head and grow up to 1/2 inch long. The larvae of all ages chew off and scrape the upper surface of leaves, causing windowpanelike damage; they do not chew holes entirely through foliage.
Sawflies develop through four life stages: egg, larva, pupa, and adult. Females insert small eggs in the margin of rose leaves. Larvae hatch and grow through about five, increasingly larger instars (growth stages). Depending on the species and situation, rose sawflies pupate in cocoons on leaves, in organic litter beneath plants, or in a cell in twigs or the stub end of cut roses. Rose sawflies in California have one or more generations per year.
Larvae chew and scrape the leaf surface, chew entirely through foliage, or both varying by the age and species. Feeding by sawfly larvae can make foliage unsightly and when severe may reduce the subsequent blossoming, but does not threaten the survival of otherwise-healthy roses.
Natural enemies keep many sawfly populations low and can cause outbreak populations to soon decline. Fungal and viral diseases, insectivorous birds, parasitic wasps, predaceous beetles, and small mammals commonly feed on and kill sawflies.
Handpick larvae or clip off and dispose of infested foliage if rose sawflies are on a small portion of the plant. Larvae are relatively easy to control if they are thoroughly sprayed with almost any insecticide, including horticultural or narrow-range oil, insecticidal soap, neem oil, or spinosad. Spinosad can adversely affect bees and certain natural enemies. Because it is toxic to bees for several hours after the spray has dried, do not apply spinosad to plants that are flowering.
Bacillus thuringiensis (Bt) is not effective against sawfly larvae because they are not caterpillars, the larvae of butterflies and moths (Lepidoptera).
Avoid applying broad-spectrum, persistent insecticides, such as carbamates (carbaryl, or Sevin), organophosphates (e.g., malathion), and pyrethroids (e.g., bifenthrin, cyfluthrin, fluvalinate, and permethrin); these are harmful to bees and natural enemies and some products move to contaminate surface water and adversely affect aquatic organisms.
See Rose Sawflies (Roseslugs) from the Sacramento Rose Society, The Rose Slugs from the U.S. Department of Agriculture, and Roseslug from Oregon State University for more information and photographs.
Adapted from Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Statewide Integrated Pest Management Program (UC IPM).
Adult bristly roseslug.
Larval chewing damage of bristly roseslug.
Larva of bristly roseslug.
Larva of roseslug and its chewing damage.