Recognize and fight successfully

A brief introduction to the walnut fruit fly

The walnut fruit fly is a fruit fly (formerly Trypetidae, now Tephritidae) within the large group of flies. In terms of appearance and way of life, it is similar to the European one Cherry fruit fly (Rhagoletis cerasi), of which she is a relative.

Here is a brief optical portrait of the walnut fruit fly:

Color: orange-brown
Size: 4 to 8 mm
Special features: eye-catching wing markings (black bands), yellow back label

The walnut fruit fly forms only one generation per year. The pupae overwinter in the ground. The adult flies hatch from the end of June. The main flight time of the insects only covers the month of July, but they are sometimes still on the move until September.

Larvae as a threat

The walnut fruit fly lays its eggs in the green peel of the walnut. This is where the whitish-yellow larvae stay and feed on the pulp, which then becomes soft, black and slimy.

Note: There can be over 25 larvae in a single walnut fruit bowl!

After three to five weeks of feeding activity, the Fly larvae fall out of the nut (or fall to the ground with it). They then bury themselves in the ground, where they pupate and form the new generation of flies in the next year.

Symptoms of a walnut fly infestation

As already mentioned, the pulp is made by the feeding activity of the larvae

• soft,
• black and
• slimy.

When you open the fruit bowl, you will find the light-colored larvae in the pulp.

Note: If the infestation is very severe, the nut kernel is also affected, which makes the walnut inedible.

Caution: risk of confusion!

Also with fungal infections such as Marssonina disease and with bacterial walnut brandy it comes to externally black fruit peels. This means that the discoloration alone does not mean that an infestation with the walnut fly must be the cause without a doubt.

Prevent and control walnut fruit flies

• Destroy infected fruits immediately. But: Do not dispose of it on the compost, burn it or dispose of it as hazardous waste (otherwise risk of infection).
• Cover the ground under your walnut tree before the fruit falls as well as in spring / summer (from the end of June). In this way you prevent pupation or overwintering) in the ground and also the hatching or fly out of the flies.
• From July, set up yellow boards to catch some of the adult flies.