Cynipidae. -- The gall wasps are divided into three subfamilies, of which two (Eucoilinae and Charipinae) are parasitic and the third (Cyniplnae) is gall makers or gall inquilines; a little over a hundred species of the first two subfamilies occur in the United States, compared with some 640 Cyniplnae (Borror et al., 1989).
There are ca. 1325 identified species of these very small insects, with about 362 species of 37 different genera in Europe and ca. 805 species in North America.
Reproduction is a two-sex propagation, that includes parthenogenesis where the male is not required.. Most species have an alternation of generations with one two-sex generation and one parthenogenic generation per year. The various generations differ mainly in appearance and the kind of plant galls they induce.
Most gall wasp larvae develop in the plant galls that they create, but there are also many inquiline species of other gall wasps, e.g., Synergus.
The plant galls are formed right after the eggs are laid. Stimuli for gall formation is not completely understood, but both chemical, mechanical and viral triggers are suspected. The hatching larvae derive nourishment from the nutritive tissue of the galls, in which they are well-protected from the external environment. The host plants and the size and shape of the galls are specific to most species. About 72% of species live on oak trees, and galls occur on almost all parts of the trees . Other species live in eucalyptus trees, rose bushes or maple trees, as well as many herbs. Identification of the species facilitated by knowing the kind of galls produced.
Galls give the developing wasp a refuge, but other wasp species may penetrate this defence and parasitize the larvae within. Some of these parasitoids use their long, ovipositor to bore into the gall and lay an egg on the gall maker. These parasitoids may also be parasitized by other wasp hyperparasitoids.
The Oak gall wasps (Cynipini) have been studied by Stone et al (2008). They are distinguished by possession of complex cyclically parthenogenetic life cycles and the ability to induce a wide diversity of highly complex species- and generation-specific galls on oaks and related trees. The galls support species-rich, closed communities of inquilines and parasitoids that are valuable in community ecology. The authors reviewed advances in the ecology of oak cynipids, with emphasis on life cycles and the dynamics of interactions between host plants, gall wasps, and natural enemies. The importance of gall traits in structuring oak cynipid communities are emphasized and evidence for bottom-up and top-down effects across trophic levels are discussed.
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Gauld, I.D., Bolton, B. (1988): The Hymenoptera, Oxford Univ. Press.
Piper, Ross (2007), Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, Greenwood Press.
Stone GN, Atkinson RJ, Rokas A, Aldrey JL, Melika G, Acs Z, Csóka G, Hayward A, Bailey R, Buckee C, McVean GA. 2008. Evidence for widespread cryptic sexual generations in apparently purely asexual Andricus gallwasps. Mol Ecol. 2008 Jan; 17(2): 652-65.
Yudell, Michael (July 1), "Kinsey's Other Report", Natural History 108 (6), ISSN 0028-0712