Putoniella pruni - Prunus spinosa

24 Apr, 2026

Gall in situ on host plant in natural setting

🌿 Observation

Main diagnostic view of erineum (mite-induced leaf deformation)

While searching for galls on Quercus cerris (Turkey Oak), I didn’t find anything on the oak itself. Instead, my attention shifted to a nearby Prunus spinosa (Blackthorn), where I found these galls.

The red/white galls are hard to miss if you look close enough. They sit on the midribs of the leaves. Various sizes, from about 3 mm to about 3 cm long. I found several, mainly on the lower leaves.

🔬 Notes / Identification

To identify this gall, I worked through a dichotomous key for gallers associated with Prunus.

The gall is located on the leaf, and clearly represents a structured deformation rather than general discoloration or damage.

This rules out:

• aphids, which typically cause leaf curling
• mite-induced erinea, which produce hairy or felt-like growth
• fungal infections, which tend to create spots or diffuse distortions

Instead, the leaf shows a distinct, well-defined gall:

• a firm, elongated swelling
• positioned along the midrib
• often reddish in colour
• with a slit-like opening on the upper surface

When opened, orange larvae are present inside.

This combination of features leads directly to:

→ Putoniella pruni

(Identification based on a dichotomous key for Prunus gallers (see Bladmineerders))

🌱 Context / Ecology

Putoniella pruni is a gall midge that primarily targets the leaves of Blackthorn (Prunus spinosa) and occasionally other plum species. Its lifecycle is closely tied to the seasonal growth of its host plant:

• Adult Emergence (Spring): Adult midges emerge from the soil in April and May. The adults are tiny, delicate flies that are short-lived and generally do not feed.
• Egg Laying: Females lay eggs on the developing tissue of young Blackthorn leaves.
• Gall Formation: As the larvae hatch and begin to feed, their presence stimulates the plant to grow abnormal tissue (the gall) around them. This provides the larvae with both food and shelter.
• Larval Stage: The larvae, which are notably orange in color, develop inside the gall throughout the late spring and early summer.
• Hibernation (Late Summer/Autumn): When the larvae are fully grown, the gall opens, allowing them to drop to the soil, where they hibernate through the winter before pupating the following spring.

📎 Related

#Gall