Common name: roseslug sawfly
Scientific name: Endelomyia aethiops
Hosts: Wild and cultivated rose plants serve as hosts for roseslug sawflies.
Roseslug sawflies are native to Europe, but now span across the United States and Canada.
Despite the name, roseslugs are not slugs. The adults are sawflies, insects that are related to bees and wasps. The young larvae are often mistaken for caterpillars, but they are completely different. They can appear similar to slugs due to their slime-like coating.
Damage
The main damage from roseslug sawfly is to the leaves of host plants. The larvae feed on the outer layers, leaving the veins untouched and a thin brown layer of tissue intact.
Larval feeding occurs from May to mid-June.
What remains of the leaves desiccates and turns brown, but this cosmetic damage typically does not cause long-term harm to the plant.
If the host plant is heavily defoliated it may suffer from stress, causing it to be more vulnerable to other pests and diseases.
Life Cycle
Roseslug sawflies have a one-year life cycle. They overwinter in the soil as pupae. Adults emerge in the spring.
Adults are just under ½-inch long, are glossy black, and have two sets of wings.
Upon emergence, they lay eggs along the underside edges of rose leaves. The sawfly deposits a single egg at a time into a small hole in the leaf created by its saw-like ovipositor.
After a few weeks, larvae hatch and the young larvae begin feeding on the leaves. The larva has a brown head and an elongated, somewhat translucent light green body. It is about ½-inch long. Young larvae feed on the outer layers of the leaf, leaving the veins and inner layers of tissue intact. The older larvae may chew holes through leaves. This feeding lasts for a month before they drop to the soil to pupate.
Management
Cultural Management
Look for roseslug sawflies in mid-spring to catch them early and have adequate time to control them before damage becomes more severe.
On hosts with a minimal infestation, the affected leaves can simply be removed and the larvae killed.
The force of spraying water aimed at both the top and underside of leaves can also be used to knock larvae off the host plant. It is best to spray earlier in the day to allow the leaves to dry before night to avoid promoting conditions for fungal leaf diseases.
Biological Management
Avoiding or minimizing use of chemical treatments will preserve beneficial natural enemies that can help reduce roseslug sawfly populations.
Chemical Management
If infestation is advanced, chemical insecticides may be used, but should not be used for prevention.
Insecticidal soaps are a safer choice for beneficials than most other insecticides.
To protect pollinators and other insects, chemical treatments should not be sprayed when flowers are present on the host plant.
The pesticide information presented in this publication is current with federal and state regulations. The user is responsible for determining that the intended use is consistent with the label of the product being used. Use pesticides safely and wisely; read and follow label directions. The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum.
For more information, contact The Morton Arboretum Plant Clinic at 630-719-2424 or plantclinic@mortonarb.org.