Gall Wasp - Reproduction and Development

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 alternation 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, such as those of the genus Synergus.

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, mechanical and viral triggers. The hatching larvae nourish themselves with the nutritive tissue 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 the majority of gall wasps, whereas about 70% 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 eucalyptus trees, rose bushes or maple trees, as well as many herbs. Frequently, the determination of the species is much easier through observation of the galls produced rather than the insect itself.