**Gooseberry Sawflies** (*Nematus ribesii*), sometimes called the Currant Sawfly, are common, invasive insect pests primarily of **currants and gooseberries** throughout the Northern Hemisphere. They are not true flies, but wasps whose larvae (caterpillars) cause severe damage by rapidly **defoliating** the host plants. Larval feeding often begins early in the season, and if left unchecked, the bush can be completely stripped of leaves within days, severely impacting the year’s fruit yield.
Taxonomy and Classification
Gooseberry Sawflies belong to the order Hymenoptera (sawflies, wasps, bees, and ants), family Tenthredinidae. They undergo complete metamorphosis. Sawfly larvae are often mistaken for moth caterpillars, but they can be distinguished by the number of prolegs (fleshy, non-segmented abdominal legs): sawflies typically have six or more pairs, while true moth caterpillars have five or fewer pairs.
Physical Description
The **adult sawfly** is a small, stout, yellow and black insect, resembling a wasp but lacking the pinched waist. It does not sting.
The **larvae** are the destructive stage, growing up to $3/4$ inch long.
- **Appearance:** Initially green, they become pale green with prominent **black spots** all over the body as they mature.
- **Behavior:** They are gregarious (feeding in groups) and often begin feeding deep within the bush, making their initial damage hard to spot until the population has grown significantly.
- **Eggs:** Laid in neat rows along the underside of the main leaf veins.
Distribution and Habitat
Gooseberry Sawflies are found across Europe, North America, and parts of Asia, wherever currants (*Ribes* spp.) and gooseberries are cultivated. Their habitat is the foliage of these host plants. They can have multiple, overlapping generations per year, making late-season control crucial.
Behavior and Damage
The sawflies overwinter as prepupae in cocoons buried in the soil near the host plant. Adults emerge in spring, and the females lay eggs on the newly emerged leaves.
- **Rapid Defoliation:** Larvae are voracious feeders, quickly chewing holes in leaves and eventually stripping the entire branch or bush, often starting with the lower, interior leaves.
- **Crop Loss:** Early season defoliation, particularly before the fruit has ripened, causes the plant to fail to photosynthesize, resulting in stunted fruit development, poor yield, and reduced health for the following season.
- **Multiple Generations:** In favorable climates, a second or third generation can appear in summer, targeting newly emerged foliage.
Management and Prevention
Control is highly effective if applied early upon detection.
- **Monitoring (Key):** Regularly inspect the lower, inner leaves of gooseberry and currant bushes starting at bud break for the first tiny larvae or the rows of eggs.
- **Hand Picking:** Since they feed in groups, small populations can be controlled by simply picking off the infested leaves or knocking the clusters of larvae into a bucket of soapy water.
- **Chemical Control:** The bacterium **_Bacillus thuringiensis_ (Bt)** is **ineffective** against sawfly larvae, as they are not true caterpillars. Effective treatments include horticultural oil or insecticidal soap for small infestations, or a targeted spray of an appropriate, non-persistent insecticide for heavy infestations.
- **Soil Treatment:** Cultivating the soil shallowly around the base of the bushes in late fall or early spring can expose and kill the overwintering pupae.
Conservation and Research
Gooseberry Sawflies are managed as key garden pests. Research focuses on identifying resistant cultivars of *Ribes* and utilizing natural parasitic wasps that attack the sawfly eggs.