Imported Currantworm (Currant Sawfly)

Taxonomy

Domain	Eukarya
Kingdom	Animalia
Phylum	Arthropoda
Subphylum	Hexapoda
Class	Insecta
Subclass	Pterygota
Infraclass	Neoptera
Superorder	Holometabola
Order	Hymenoptera
Superfamily	Tenthredinoidea
Family	Tenthredinidae
Subfamily	Nematinae
Tribe	Nematini
Genus	Nematus

Scientific Name

Nematus ribesii

Common Name

imported currantworm

Compiled by Whitney Cranshaw, Colorado State University

Nematus ribesii (Scopoli)
Hymenoptera: Tenthredinidae

Hosts:

Currants, gooseberry

Damage and Diagnosis:

The larvae chew the leaves of currants and gooseberries, often extensively defoliating the plant early in the season. Foliage in the interior of the bush is first damaged but all leaves may be eaten. Yield and quality of fruit can be affected by this injury.

The larvae are generally a light green-gray with numerous black spots. (Larvae that have just molted are light green.)

Associated Insects:

Larva of a moth, the currant spanworm, Itame ribearia (Fitch), is another insect that often feeds on the leaves of currant and gooseberry. The larvae of this insect are also spotted, but are a type of inchworm with a distinctive looping walk. These are the immature stage of a small moth and the caterpillars can be controlled with Bacillus thuringiensis, which is not effective against sawflies.

Life History and Habits:

Imported currantworm eggs.

Imported currantworm larvae.

The imported currantworm spends the winter in a cocoon in the soil around previously infested currants and gooseberries. The adults, a dark brown wasp about one third inch long, usually emerge early in spring, although wet cool weather may delay emergence by several weeks. After mating, the female lays eggs in rows inserted into the main veins of the leaf underside. The larvae hatch about seven to ten days after eggs are laid and at first chew small shotholes in the leaf interior. Later they disperse throughout the plant and feed along the leaf margins, becoming full-grown in about three weeks. Young larvae are pale green, but develop distinctive dark spots as they grow and reach a size of about 3/4 inch.

The full-grown larvae drop to the ground and form a cocoon. Some pupate and emerge in late June and July, producing a small second generation. The majority remain dormant and emerge the following year.

Management:

In small plantings, the larvae can be controlled by hand-picking or shaking. Careful examination of the newly emerging leaves can also identify the eggs which may be crushed. Most eggs and larvae will be found in the interior of the shrub.

At the end of the season, rake and remove all the debris away from the base of the plants. Most of the overwintering cocoons occur in this leaf litter and can be destroyed by this practice.

Chemical control options are limited on currants and gooseberries. Some formulations of malathion and pyrethrins allow use on this crop and are effective for imported currantworm control. However, be sure to check labels carefully to insure that use on the crop is specifically allowed.

Sprays of irritants, such as soaps, dilute dishwashing detergent, and wood ashes, can be effective controls against younger larvae.

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.