gall wasp

Small (only a few millimetres long), dark-coloured insect with a compressed abdomen. Most gall wasps form galls, though a few live within the galls formed by other species; these are called inquilines. Others feed on gall-formers and inquilines.

Classification
Gall wasps are in the family Cynipidae, order Hymenoptera, class Insecta, phylum Arthropoda.

The exact reactions which lead to gall formation in the host plant are little understood. Basically it is a reaction of the cells of the plant to the presence of the larva.

Complex life history
The oak-apple gall is caused by species Biorhiza pallida and both winged males and wingless or vestigial-winged females emerge from these galls. After mating the females lay their eggs in the root of the same host plant, thus producing root galls. In the following spring only wingless females are produced. These females climb up the oak tree and produce the characteristic oak-apples, thus repeating the life cycle.

Rose galls are often produced by Diplolepis rosae. These gall wasps usually reproduce asexually; the females are about 4 mm/0.2 in long; parts of their abdomens and legs are yellow-red, while the rest of the body is black. Males of this species have been observed only rarely. The galls are a mass of reddish filaments within which are found a number of sealed chambers enclosing larvae. The larvae feed on the gall tissue.