Currant stem midge

The currant stem midge (Gralliclava horrens, formerly Resseliella ribis) is a small dipteran insect belonging to the Cecidomyiidae family, known for attacking currant bushes.

Adult midges are tiny, delicate flies, approximately 2 mm in length, with transparent wings. They are most active during the flowering period of currants.

The larvae are legless, white to yellowish in color, and grow to about 2-3 mm. They develop in groups under the bark of stems, which is the most destructive stage of their life cycle.

These insects overwinter as mature larvae in cocoons, either in the soil beneath the host plant or in sheltered cracks of the woody stems.

Their life cycle consists of multiple generations per year, with the emergence of adults highly dependent on temperature and local microclimate conditions.

The midge primarily targets black currant, though red and white currants can also be affected, especially when the bark has existing wounds or cracks.

Larvae feed on the cambium and phloem tissues, effectively girdling the stem. This disrupts the transport of water and nutrients throughout the branch.

This damage causes the leaves to wilt and the stems to die back prematurely. The weakened stems are prone to breaking under light wind or mechanical stress.

In addition to direct feeding, the injured bark serves as an entry point for various wood-decaying fungi, which further accelerates the decline of the plant.

Heavy infestations can lead to significant yield loss and the complete death of individual canes, drastically reducing the productivity of the currant plantation.

Early symptoms include localized discoloration of the bark, often appearing as brownish, sunken patches on the stem surface.

As the infestation progresses, the bark begins to crack or peel away, revealing the larvae underneath, which are often clustered together.

During the growing season, a key sign is the sudden wilting of leaves on one or more stems, followed by the browning and eventual death of the entire branch.

Excrement from the larvae appears as a fine, dusty brown powder, which can be seen accumulating under the loose bark.

Brittleness of the stems is a common observation; they often snap at the site of the larvae's feeding activity during maintenance work or pruning.

The most effective management strategy is rigorous sanitation, which involves pruning and destroying all infested stems to eliminate the larvae before they emerge.

Preventative measures include protecting stems from mechanical damage and using wound dressings to prevent adult midges from laying eggs in crevices.

Cultivating the soil around the base of the bushes in spring and autumn can disrupt the pupation process and reduce the population of the next generation.

Chemical control, if necessary, should be applied during the adult flight period, monitored closely via sticky traps to ensure optimal timing.

• Sanitary pruning of infested canes
• Soil cultivation around bushes
• Protecting stems from damage
• Pheromone trap monitoring
• Strategic insecticide use