About the life of the gall wasp

the essentials in brief

• There are 1400 different species of gall wasp
• We know the gall wasps mainly from gall apples, a ball rich in tannic acid, which occurs mainly on oak and which is caused by gall wasp larvae
• Plant galls are not really harmful to the plant; it usually recovers quickly
• A few species of gall wasp are used to control pests

Gall wasps at a glance

Gall wasps represent the genus Cynipidae within the hymenoptera. Worldwide there are more than 1,400 different species that are similar in their way of life. The product of the gall wasp is the so-called gall apple. This is caused by fertilized eggs that are deposited by female animals on the underside of the leaf. Galls are products of different organisms, including bacteria and mites.

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Other forms of galls:

• Marrow galls
• Walling galls
• Hair or felt galls
• Roll or bag galls
• Fold or cloak galls

Appearance

Gall wasps are between one and three millimeters long. They are inconspicuously drawn and mostly colored black. The males have one antennae more than females. In the side view, the front body is usually very short and high, while the abdominal segment is round to oval in shape. Females of different species differ in their laying sting. This can be almost body length or very short.

confusion

Gall wasps can easily be confused with the sister family Figitidae. These hymenoptera should be viewed under a microscope so that they can be clearly distinguished from the gall wasps. Only gall wasps make the typical gall apples. Figitidae species parasitize on other insects.

Gall wasp on oaks

Gall wasps particularly like oak leaves. Even if the larvae of the gall wasps cause only minor damage, the oak defends itself by producing tannins that form the gall apple. This gall apple contains up to 60% tannic acid, which in the past was mainly used for tanning leather and as color, mixed with ice salts. This so-called iron gall ink is still used today for signing international treaties.

Harmful or useful?

In most plants, plant gall caused by gall wasps does not cause any significant damage. The oak trees that are often affected in Germany regenerate very quickly from an infestation. While an alien species may be a pest, some species are even useful.

Gall wasps do no harm and do not need to be fought. But be vigilant when caring for a sweet chestnut in the garden.

pest

Worldwide, the Japanese chestnut gall wasp is considered to be the most dangerous pest that can occur on the chestnut. If the wood is heavily infested, it will develop fewer flowers and the harvest will be less. Individual observations have been made in Central Europe since 2002. The species has appeared in Germany since 2013. Finds from Hesse, Baden-Württemberg and North Rhine-Westphalia are documented here.

Beneficial organism

There are few gall wasps that live parasitically on other insects. The larvae of these species usually have several small teeth or cutting edges and prove to be useful pest fighters. There are gall wasps that are considered natural enemies of the codling moth. The codling moth attacks pears and reduces the harvest.

Fight gall wasps?

Even if the leaves of a plant are partly covered with galls, gall wasps do not cause any significant damage. Therefore, you do not have to fight the insects. If you find the growths bothersome, you can cut off the shoots and leaves with sharp scissors and dispose of them.

Only with the sweet chestnut should you examine the plant galls a little more closely. If the Japanese chestnut gall wasp is responsible for the growths, report the infestation. The effect of control measures is still being researched. Hardly any results are available on their effectiveness. Mechanical control is recommended in the early stages.

Tips

Encourage natural opponents that target the insects. The enemies include hatching wasps and wasps. It can be effective if you lime the earth or apply preparations containing paraffin oil.

Development and way of life

Females lay their eggs in carefully selected locations. They are based on the development stage of the leaves so that their larvae are optimally supplied. The galls can also arise on flowers and buds, twigs and stems or on the roots. Larvae pupate within the galls. The adult insect eats a circular hole in the shell with its mouthparts and frees itself in this way.

bile

Gall wasps trigger a growth in the leaf tissue when they lay their eggs. Females give off hormonally acting substances through their ovules, so that the growth programs of the plant are modified. A bile is created in which a larva develops at a time. The insects have a purely vegetable diet.

Each bile is shaped specifically for the species and consists of a hard shell and a soft inner tissue. Different numbers of chambers can be formed in the plant bile, in each of which a larva lives and eats the plant tissue. After hatching, it ensures that the bile continues to develop.

Where do gall wasps live?

Gall wasps are tied to certain climatic zones, with many species being introduced throughout the world. They specialize in host plants and cannot survive without them. In Germany the native species show a very specialized way of life.

distribution

Gall wasps live in the temperate latitudes of the northern hemisphere. The majority of all genera and species are common in the Mediterranean region and around the Black Sea. There are no gall wasps in the tropics. Some species were able to spread to southern mountain regions. In the south of America and Africa only four genera have been described so far. There are around 100 species in the northern parts of Central Europe.

Host plants

Gall wasps develop on dicotyledons. There is only one species in the world that lays its eggs on a monocot. Many species have specialized in certain plant species or genera. The original species are found on the poppies, daisies and mint plants. One line of development has specialized in rose plants. There are gall wasps that only occur on oaks. Few species also colonize other deciduous trees such as maple, beech or willow.

• Oak : Common oak gall wasp and oak lentil gall wasp
• Rose : Common rose gall wasp
• Chestnut : Japanese chestnut gall wasp,
• Bindweed : Diastrophus smilacis, North American species

Species and galls

In Germany there are mainly species that appear as gall formers on oaks. The common oak gall wasp is the best known species that causes characteristic galls on the underside of oak leaves. They turn reddish in color in autumn, just before the insects hatch.

Oak lentil gall wasps develop light-colored galls on the underside of the leaves, which are arranged in a lens shape. The plant galls of the species Cynips longiventris, which are characterized by their spherical shape and irregular red stripes, are striking. The galls of the sponge gall wasp, which are known as potato bile or oak apple, grow up to four centimeters in size.

Galls of the common rose gall wasp often appear on roses. These are known as sleeping apples, rose apples or bedeguar and are located on the ends of roses. They can reach a diameter of up to five centimeters and develop long hair-like outgrowths. The interior is criss-crossed by several corridors, each with a larva.

Are gall wasps dangerous?

Gall wasps are completely harmless to humans and pets. The insects cannot sting, even if the ovipositor of the female is frightening when extended. The sole purpose of this is to penetrate the plant tissue and lay the eggs there. The diet of the insects is predominantly vegetable, whereby gall wasps represent an exception within the partial order of the Legims. The majority of these hymenoptera live parasitically and lay their eggs in animal organisms.

frequently asked Questions

Where do gall wasps appear?

The native species are mainly found on oaks. They are responsible for the growths on the underside of the leaves. There are also gall wasps that specialize in roses. These species are preferred on wild roses, where they lay their eggs in the tissue of the shoot tips.

How do gall wasps live?

The female insects lay their eggs in plant tissue with the help of an ovipod. Secreted hormones ensure that the tissue proliferates. This creates a spherical protuberance that is protected by a hard shell. The larvae live inside the plant bile and feed on the tissue until they pupate.

Do I have to fight gall wasps?

Control is usually not necessary as the plants are hardly damaged. Even if a wood has tons of galls, you don't have to worry about the vitality of the plant. Only the sweet chestnut can be severely damaged by gall wasps, so that the harvest is weaker. An introduced species that does not originally occur in Central Europe is responsible for this damage. Caution is also required if the plant gall is not caused by gall wasps.

Can gall wasps sting?

These insects are unable to sting. They have nothing to do with the actual wasps and are completely harmless to humans. Gall wasps have not developed any special defense mechanisms that could be dangerous for humans or pets.

Do all galls come from the gall wasp?

There are several organisms that can cause plant gall. In addition to gall wasps, bacteria, fungi, nematodes and mites can also be used as gall-forming agents. There are also other insects that also cause plants to grow. If you find a bile, identify it and determine the type.