Rose Sawflies

Rose sawflies adults are small primitive wasps who’s larvae look like tiny little caterpillars. These larvae, commonly called rose slugs, are voracious feeders and feed almost exclusively on rose leaves. If their numbers are high enough they can quickly defoliate an entire rose bush. Larvae feeding damage appears as skeletonized leaves that look like window panes. As the feeding continues large holes are chewed through leaves and finally entire leaves are devoured all except the midrib. The insect gets it’s name from the saw-like blade located at the tip of the female wasps abdomen that is used to insert their eggs into rose leaves or rose canes (depending on the species).

There are 4 species of sawflies that feed on roses leaves here in Canada and the U.S.A.

  1. Curled Roseslug Sawfly (Allantus cinctus)
  2. Bristly Roseslug Sawfly (Cladius difformis)
  3. European Roseslug Sawfly (Endelomyia aethiops)
  4. Large rose sawfly (Arge pagana and Arge ochropus)

Curled Roseslug Sawfly (Allantus cinctus)

The curled roseslug occurs in England, Europe, Canada and The United States.

Identification: The adults have a black head and thorax. The abdomen is also black but has a thick pale coloured band across it. They measure 6 to 9 mm (1/4″-1/3″) in length. The larva are light green in colour with white dots on the thorax and abdomen. The head is yellowish with black eye spots. They measure 13 to 19 mm (1/2 to 3/4″) long with tapered bodies. When they are not feeding they curl up, (thus their name), blending seamlessly into the leaf colour.

Life Cycle: The female sawfly lays her eggs in rose leaves in the spring. They hatch a few weeks later (around late May/early June) and the larvae begin feeding on the rose leaves. They start out by skeletonizing the leaves but as they mature the entire leaves, except the main veins, are devoured. The larvae then bore into the rose twigs or into the pith of pruned canes, where they develop into a pupa. The adult sawflies emerge from the canes, mate and the female once again lay their eggs inside the rose leaves. There are generally two generations per year. They are active from May to August. In addition to roses these sawflies can also be found on strawberries.

Management: Monitor your roses regularly for their presence. Larvae can be removed by hand where practical. Larvae can be washed off the leaves using a strong jet of water. Heavily infested leaves can be removed if the infestation is more localized. Prune canes back below the spot where the insect has bored into the cane. Spraying the larvae with horticultural oil or insecticidal soap will kill the larvae. For heavy infestations a systemic pesticide may be warranted.

2 curled roseslug sawflies. When they are curled up at rest on the underside of the leaves they blend into the leaf colour almost seamlessly and are very difficult to spot without a handlense.
3 curled sawfly actively feeding on the underside of a leaf.
Typical feeding damage caused by curled rose sawflies.
Curled rose sawfly actively feeding on the underside of a rose leaf.

Bristly Roseslug Sawfly (Cladius difformis)

The bristly roseslug is found in Europe, Siberia, Canada and United States. It does not appear to occur in warm climates.

Identification: The female wasps are about 16mm (5/8″) long and are shiny black with yellowish-orange markings on their body. The males are much smaller, about 10mm (3/8″) long (Villegas B. 2002). The caterpillar-like larvae are pale green in colour and covered with short, hair-like bristles that can be seen with a hand-lens. A full grown larva measures up to 16 mm (5/8″).

Life Cycle: Bristly rose slug sawflies overwinter as pupae in the soil near their host plant. The adults emerge in May or June. They mate and then the female wasps use a saw-like blade located at the tip of their abdomen, to insert eggs into the leaf. A short while later the newly emerged larvae begin to feed. The young larva begins feeding as a skeletonizer on the underside of the leaves and as it matures it chews large holes in the leaves. The larvae feed for 2-3 weeks then the full grown larvae drop to the ground to pupate. There are as many as six generations each year (Baldo Villegas 2002). In addition to roses these sawflies can also be found on raspberries and strawberries.

Management: Monitor your roses regularly for their presence. Larvae can be removed by hand where practical. Larvae can be washed off the leaves using a strong jet of water. Heavily infested leaves can be removed if the infestation is more localized. Spraying the larvae with horticultural oil or insecticidal soap will kill the larvae. Systemic pesticide for heavy infestations may be be best option.

European Roseslug Sawfly (Endelomyia aethiops)

The European roseslug is found in Europe, Canada and The United States.

Identification: Adults have shinny black bodies with a few yellow makings on the body and two pairs of dusky transparent wings. They measure between 5-10 mm (1/4 to 3/8″). The larvae are light green with brown heads and are club shaped, with the head end being the larger. Their bodies are fairly translucent and their insides (guts) are visible. The larvae grow to a length of about 10 to 13mm (3/8 to 1/2″).

Life Cycle: Adult sawflies emerge in spring and lay their eggs on the underside of rose leaves. The eggs are laid singly in pockets along the margins of the leaves. The caterpillar-like larvae appear several weeks later and begin feeding at night on the upper and lower sides of the rose leaf. The young larvae skeletonize the leaves while older larvae chew holes right through the leaf. They feed for about a month, and then drop into the soil to pupate. There is typically one generation per year in North America. They are most active in May and June.

Management: Monitor your roses regularly for their presence. Larvae can be removed by hand where practical. Larvae can be washed off the leaves using a strong jet of water. Heavily infested leaves can be removed if the infestation is more localized. Spraying the larvae with horticultural oil or insecticidal soap will kill the larvae. Systemic pesticide for heavy infestations may be be best option.

European roseslug sawfly larvae and it’s damage. sawfly
European roseslug sawfly larvae and it’s damage.

Large Rose Sawfly (Arge pagana and Arge ochropus)

This sawfly is present in Europe, Asia Minor, the Caucasus, Turkmenistan, Northern Iran and Western Siberia up to Lake Baikal. It has been introduced to the northeastern United States and Eastern Canada (Wikepedia rev. Nov. 2020)

Identification: The adults measure about 10 mm (3/8″) and have yellow/orange abdomens with mainly black thorax and heads with dark, tinted wings, which are kept over the abdomen. The caterpillar-like larvae are pale green with some yellow like blotching and black spots. Larvae measure about 2.5 cm (1″) at maturity.

Life Cycle: The female sawflies use their razor like ovipository to lay about 16–18 eggs in young rose stems. The stems often split open where the eggs were laid, resulting in elongate scars (RHS n.d). The eggs hatch quite quickly and the larvae begin feeding in groups on newly emerged leaves. As the larvae mature they become more independent and feed singly on old leaves as well as young. Active from late May to October. There are two generations a year.

Management: Monitor your roses regularly for their presence. Eggs within the scars can be destroyed by running a fingernail (or equivalent) down the scar (RHS n.d) or the leaves (if there are not to many) may be removed and destroyed. Larvae can be removed by hand where practical. Larvae can be washed off the leaves using a strong jet of water. Spraying the larvae with horticultural oil or insecticidal soap will kill the larvae.

Photo credits: all photos taken by the author.

References

Boggs J.2016, Sawfly Slugged Rose Leaves, The Buckeye Yard and Garden Online, The Ohio State University Extension, Retrieved on Feb. 15, 2021 from: Sawfly Slugged Rose Leaves | BYGL (osu.edu)

Bug Guide rev.  May, 2015, Iowa State University, Species Arge ochropus – Rose Sawfly, Species Arge ochropus – Rose Sawfly – BugGuide.Net

Cranshaw W. rev, April 2016, Colorado State University, Bristly roseslug: Cladius difformis (Panzer), Retrieved on Feb. 15, 2021 from: Roseslugs – Bugwoodwiki

Missouri Botanical Garden n.d., Rose and pear slugs (sawflies), Retrieved on Feb 14, 2021 from: Rose and pear slugs (sawflies) (missouribotanicalgarden.org)

Nature Spot n.d., Large Rose Sawfly – Arge pagana, Retrieved on Feb. 15, 2021 from: Large Rose Sawfly | NatureSpot

Nature Spot n.d., Curled Rose Sawfly – Allantus cinctus, Retrieved on Feb. 15, 2021 from: Curled Rose Sawfly | NatureSpot

Oak Leaf Gardening n.d., Rose leaf-rolling sawfly – Blennocampa phyllocolpa, Retrieved on Feb. 14, 2021 from: Rose leaf-rolling sawfly – Blennocampa phyllocolpa – Problems – Oak Leaf Gardening

Raupp M.J., 2005, Sawflies- Curled Rose Sawfliy, Allantus cinctus, and Dusky Birch Sawfly, Croesus Latitarsus, Retrieved on Feb. 15, 2021 from: Sawflies – Curled rose sawfly, <i>Allantus cinctus</i>, and dusky birch sawfly, <i>Croesus latitarsus</i> — Bug of the Week (squarespace.com)

RHS n.d., Large rose sawfly, Retrieved on Feb. 14, 2021 from: Large rose sawfly / RHS Gardening

Villegas B. 2002, Rose Sawflies (Roseslugs), Retrieved on Feb. 14, 2021 from: Rose Sawflies (Roseslugs) (sactorose.org)

Wenning B. 2017, Ecological Landscape Alliance, Rose Insect Pest Alert: The Roseslug Sawfly, Hymenoptera: Tenthredinidae, Retrieved on Feb. 14, 2021 from: Rose Insect Pest Alert: The Roseslug Sawfly, Hymenoptera: Tenthredinidae – Ecological Landscape Alliance (ecolandscaping.org)

Wikepedia rev. Nov. 2020, Arge ochropus, Arge ochropus – Wikipedia

Ohnesorg W. n.d., Extension Educator, Roseslugs Fact Sheet, Microsoft Word – Roseslugs fact sheet.docx (mrwlawns.com)

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