Gall wasps are mysterious insects whose way of life remains hidden to most people. The insects develop in a completely protected environment. From the outside, these development sites are recognizable as rounded structures on the undersides of leaves. The inner workings harbor exciting secrets.

The gall wasp looks quite inconspicuous, but it can also sting

Table of Contents

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  1. the essentials in brief
  2. Characteristics
  3. Gall Wasp Oak
  4. Harmful or useful?
  5. Fight gall wasps?
  6. development and lifestyle
  7. Happen
  8. species and galls
  9. Are gall wasps dangerous?
  10. frequently asked Questions

    11. the essentials in brief

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

    Gall wasps at a glance

    Gall wasps represent the genus Cynipidae within the hymenoptera. There are more than 1,400 different species worldwide 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 or mites.

    Other forms of galls:

    • marrow galls
    • eruption galls
    • hair or felt galls
    • roll or pouch galls
    • fold or mantle galls

    Look

    Gall wasps are between one and three millimeters long. They are inconspicuously drawn and predominantly black in color. Males have one antennal segment more than females. When viewed from the side, 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 ovipositors. 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 the microscope so that they can be clearly distinguished from the gall wasps. Only gall wasps form the typical gall apples. Figitidae species parasitize on other insects.

    Cynipidae Figitidae
    upper torso section microscopically small grain, therefore matt glittering
    pronotum noticeable two lateral keels or prominent plate
    upper abdominal plate third link longest fourth link longest
    way of life mostly vegetable parasitic

    Gall wasp on oak trees

    Gall wasps are particularly fond of oak leaves. Even if the gall wasp larvae cause only minor damage, the oak tree defends itself by producing tannins that form the galls. This gall contains up to 60% tannic acid, which used to be mixed with ice salts to tan leather and used as a color. Even today, this so-called iron gall ink is used to sign state treaties.

    Galls are a pathological outgrowth of the tree to protect itself from the larvae of the gall wasp

    Harmful or useful?

    Plant galls caused by gall wasps do not cause significant damage to most plants. The oaks, which are often affected in Germany, regenerate very quickly from an infestation. While an alien species is a potential pest, some species are actually beneficial.

    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

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

    beneficial

    There are few gall wasps that are parasitic on other insects. The larvae of these species usually have several small teeth or cutting edges and prove to be useful pest controllers. 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 partially covered with galls, no significant damage is caused by gall wasps. Therefore, you do not have to fight the insects. If you find the growths annoying, you can use sharp scissors to cut off shoots and leaves and discard them.

    Only in the case of the sweet chestnut should you examine the plant galls a little more closely. If the Japanese chestnut gall wasp is responsible for the growths, you should report the infestation. The effect of control measures is still being researched. Little is known about their effectiveness. Mechanical control is recommended in the early stages.

    tips

    Encourage natural enemies that prey on the insects. Enemies include parasitic and chalcid wasps. Liming the soil or applying paraffin oil preparations may prove effective.

    development and lifestyle

    Females lay their eggs in carefully selected locations. They orientate themselves on the development stage of the leaves so that their larvae are optimally cared for. The galls can also develop on flowers and buds, branches 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

    When gall wasps lay their eggs, they trigger a proliferation in the leaf tissue. Females release hormonal substances via their ovipositor, so that the growth programs of the plant are modified. A gall develops in which one larva develops. The insects feed purely on plants.

    Each gall has a species-specific shape and consists of a hard shell and a soft inner tissue. Different numbers of chambers can be formed in the plant gall, in each of which a larva lives and eats the plant tissue. After hatching, it ensures that the gall continues to develop.

    Although the larva in the gall feeds on the leaf tissue, the damage is rather minor

    Where do gall wasps live?

    Gall wasps are tied to specific climate zones, with many species now being carried around the world. They have specialized 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 distributed in the Mediterranean region and around the Black Sea. There are no gall wasps in the tropics. Some species have been able to spread to southern mountainous regions. Only four genera have been described in southern America and Africa. About 100 species occur in the northern parts of Central Europe.

    host plants

    Gall wasps develop on dicots. 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 occur on poppies, daisies and lamiaceae. A development line has specialized in rose plants. There are gall wasps that only occur on oak trees. A few species also colonize other deciduous trees such as maple, beech or willow.

    • Oak: Common oak gall wasp and oak lens gall wasp
    • rose: Common rose gall wasp
    • chestnut: Japanese chestnut gall wasp,
    • biting wind: Diastrophus smilacis, North American species

    Roses can also fall victim to the gall wasp

    species and galls

    In Germany there are mainly species that occur as gall formers on oaks. The oak gall wasp is the most well-known species that causes characteristic galls on the underside of oak leaves. They turn reddish in autumn just before the insects hatch.

    Oak lens gall wasps develop light-colored galls on the underside of the leaf, 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, known as potato gall or squirrel, grow up to four centimeters in size.

    Galls of the common rose gall wasp are often found on roses. These are known as sleep apple, rose apple or bedeguar and are found at the ends of rose shoots. They can reach a diameter of up to five centimeters and develop long hair-like outgrowths. The interiors are traversed by several passages, in each of which a larva lives.

    Are gall wasps dangerous?

    Gall wasps are completely harmless to humans and pets. The insects cannot sting, even if the female's ovipositor is frightening when extended. This serves exclusively to penetrate plant tissue and deposit the eggs there. The diet of the insects is predominantly vegetable, which makes gall wasps an exception within the Legimma suborder. The majority of these hymenoptera are parasitic and lay their eggs in animal organisms.

    frequently asked Questions

    Where do gall wasps occur?

    The native species are mainly found on oaks. They are responsible for the growths on the undersides of leaves. There are also gall wasps that specialize in roses. These species prefer 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 a ovipositor. Secreted hormones ensure that the tissue proliferates. This forms a spherical protuberance protected by a hard shell. The larvae live inside the plant gall and feed on the tissues until they pupate.

    Do I have to fight gall wasps?

    Control is usually not necessary as the plants are hardly damaged. Even if a shrub has masses of galls, you do not have to worry and the vitality of the plant. Only the 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 pattern of damage. Caution is also required if the plant galls are 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.

    Are all galls from the gall wasp?

    There are several organisms that can cause plant galls. In addition to the gall wasps, bacteria, fungi, nematodes and mites can also be considered as gall formers. There are also other insects that also cause growths on plants. If you find a gall, you should identify it and determine the species.

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Animals in the garden