PROCEEDINGS OF THE CALIFORNIA ACADEMY OF SCIENCES FOURTH SERIES Vol. XXXV, No. 20, pp. 477-586; 70 figs. November 14, 1968 THE CLASSIFICATION OF THE TRICHOGRAMMATIDAE (HYMENOPTERA: CHALCIDOIDEA) By Richard L. Doutt Lhiiversity of California, Berkeley and Gennaro Viggiani Istituto di Entomologia Agroria "F. Silvestri," Portici, Italy Introduction The minute, parasitic wasps which comprise the family Trichogrammatidae are widespread, abundant, and obviously successful organisms that form a mor-phologically unique segment of the superfamily Chalcidoidea. Their small size reflects their mode of development as internal parasites of various insect eggs. Thus the adults of Megaphragma may measure no more than 0.18 mm. in total length for they develop within the eggs of thrips. The minuteness of such winged and vagile insects has undoubtedly increased their chances of dispersion by wind. Evidence suggesting this is seen in the world-wide distribution of tricho-grammatids and in their usual occurrence as part of the arthropod fauna on small, remote, and isolated oceanic islands. Large numbers of species and indi-viduals are regularly taken in suction traps designed to sample insects from a passing column of air. Not only are trichogrammatids likely to become potential colonists by being carried by wind into new areas, but the group as a whole appears to have had sufficient genetic plasticity to exploit a tremendous variety of host insects in very diverse habitats. Some trichogrammatids are adapted to hosts in hot, dry deserts while others have become aquatic to attack eggs of such insects as dragon-flies or water beetles.