Gall wasp
From Biocrawler, the free encyclopedia.
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Gall wasps (Cynipidae), also called Gallflies, are a family of the order Hymenoptera and are classified with the Apocrita suborder of wasps in the superfamily Cynipoidea. About 1300 species of this generally very small creature (1-8 millimeters) are known worldwide, with about 375 species of 36 different genera in Europe and some 800 species in North America.
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Features
Like all representatives of Aprocrita, gall wasps have a distinctive body shape, the so-called wasp waist, a term which is also used to describe corsets. To that end, the first abdominal segment (the Propodeum) is conjoined with the thorax segments, while the second abdominal segment forms a sort of shaft, the petiolus. The antennae are straight and consist of 12 to 16 segments. In many varieties the backside of the thorax is banded. The wings are very simply structured. On the rear tip of the abdomen, the female has an ovipositor for depositing eggs.
Reproduction and Development
The reproduction of the gall wasp is partly pure two-sex propagation, partly pure parthenogenesis, in which a male is completely unnecessary. With most species, however, there is an alteration of generations with one two-sex generation and one parthenogenic generation annually. This process differentiates the various generations primarily in their appearance and the form of the plant galls they induce.
The larvae of most gall wasps develop in characteristic plant galls they induce themselves, however many species are also inquilines of other gall wasps.
The plant galls mostly develop directly after the female insect lays the eggs. The inducement for the gall formation is largely unknown; discussion speculates as to both chemical and mechanical triggers. The hatching larvae nourish themselves with the fibers of the galls, in which they are otherwise well-protected from external environmental effects. The host plants and the size and shape of the galls are specific to each type of gall wasp, whereas about 80% of the known species live in various types of oak tree. One can find galls on nearly all parts of such trees, some on the leaves, the buds, the branches, and the roots. Other species of gall wasp live in rose bushes or maple trees, as well as many other host plants. Frequently, the determination of the species is much easier through observation of the galls produced rather than the insect inself.
The larvae of some species, such as those of the genus Synergus, build galls inside the galls of other gall wasps; thereby destroying the original gall in most cases.
Types
Most species of gall wasp live as gall-builders in oak trees. One of the most well-known of these oak gall-builders is the Common Oak gall wasp (Cynips quercusfolii), which builds characteristic two-centimeter long galls on the underside of oak leaves. These turn reddish in the fall and are commonly known as oak apples. Light lentiform galls on the underside of the same leaves are built by Neuroterus quercusbaccarum; darker ones with bulging edges are built by Neuroterus numismalis. Also striking are the galls of Cynips longiventris, which likewise can be found on the underside of leaves, and are recognizable for their spheroidal shape and irregular red streaks. The Oak potatoe gall wasp (Biorrhiza pallida), which also lives in oaks, has round galls that grow to four centimeters. These are known colloquially as oak potatoes. The latter type of gall is built by this type of wasp not on the leaves, but on the roots of the oak. On the buds of young oak twigs, on can often find the hard-shelled galls of Andricus kollari and Andricus quercustozae.
The galls of the Rose gall wasp (Diplolepis rosae) are also distinctive and are known as Bedeguar. These are found on the shoots of roses and have a length of up to five centimeters with red long-haired outgrowths. Inside the galls are several chambers, which at any one time can be occupied by larvae.
Additional Information
The galls of several species, especially Mediterranean variants, were once used as tanning agents.
A rose gallnut with stem makes a long-lasting bouquet adornment.
Literature
- Gauld, I.D., Bolton, B. (1988): The Hymenoptera, Oxford
- Honomichl, K., Bellmann, H. (1994): Biologie und Ökologie der Insekten (In German)
References
- This article is based on a translation of the corresponding article from the German Biocrawler. Basic information corrected by Johan Liljeblad (with a PhD on gall wasps).
