Hawthorn gall midge

The Hawthorn gall midge (Resseliella crataegi) is a tiny insect belonging to the order Diptera and the family Cecidomyiidae. Adult midges are very small, fragile flies that are rarely noticed by casual observers.

The larvae are legless, whitish or yellowish maggots. They are responsible for the damage, as they feed inside plant tissues and trigger the formation of specific galls, which provide both shelter and nutrients.

The life cycle involves complete metamorphosis. Eggs are laid on new shoots or buds, and the resulting larvae bore into the tissues to begin their development, causing the plant to react by forming a gall.

Pupation typically occurs in the soil or within plant debris under the host tree. The insects overwinter as pupae, emerging in spring when temperatures are favorable for mating and oviposition.

Identification is primarily based on the galls produced rather than the insects themselves, which are extremely difficult to spot in the field due to their size.

This pest specifically targets hawthorn species. By feeding within the twigs and buds, the larvae interfere with the plant's vascular and structural integrity, leading to pathological growths known as galls.

Gall formation disrupts nutrient transport, which limits the growth of affected branches. In severe cases, the tips of the shoots may wither or die entirely, leading to a loss of the plant's natural shape.

The compromised tissues of the galls are prone to secondary infections. Bacteria and fungi often invade these sites, causing rot and further weakening the structural stability of the plant.

Young plants or saplings are the most vulnerable, as infestation can stunt their development for several seasons. Constant damage reduces the decorative value of hawthorn in landscaping and gardens.

Overwintering becomes more dangerous for infested plants, as the weakened branches are less cold-hardy, leading to increased frost damage and dieback of the crown.

The most distinctive symptom of infestation is the appearance of galls—abnormal, localized swellings on the shoots. These can range in size and color depending on the stage of the larva's development.

Leaves associated with the infested shoots often appear distorted, curled, or stunted. This foliage may turn yellow or brown earlier than expected, indicating impaired nutrient uptake.

A closer look at the bark of the shoots might reveal signs of splitting or necrosis around the gall site. In some cases, tiny exit holes can be seen after the adult midges emerge.

During the active growing season, gardeners may notice that certain branches are growing in a zigzag pattern or appear twisted. This is a classic visual indicator of gall midge presence.

• Swollen galls on young twigs.
• Distorted or curled leaves near the infestation.
• Stunted shoot growth and dieback.
• Premature yellowing of foliage.
• Localized necrotic bark tissue.

The most reliable control method for homeowners is pruning. By cutting out and destroying affected shoots before the larvae vacate the galls, you can significantly reduce the local population.

Sanitation is key to preventing re-infestation. Clearing away all fallen leaves and garden debris from under the bushes prevents larvae from successfully overwintering near the host plant.

Soil management, such as hoeing or tilling the area beneath the canopy during spring and autumn, disturbs the pupae and exposes them to predators and harsh environmental conditions.

Chemical control with systemic insecticides is reserved for extreme cases of infestation. It should be applied during the early stages of bud burst when adults are active and laying eggs.

Implementing biological control, such as encouraging natural predators like ladybugs or lacewings, as well as using microbial pesticides, helps maintain a balance and suppress midge numbers over time.