Seed-infesting chalcids of the genus Megastigmus Dalman, 1820 (Hymenoptera: Torymidae) native and introduced to the West Palearctic region: taxonomy, host specificity and distribution.
A total of 21 species (including one new to science, i.e. M. atlanticus sp. nov.) of Megastigmus seed chalcids are recognized in Europe, North Africa and Asia Minor. From 1977 to 2001, some 5260 seed samples were collected from a total of 118 tree and shrub species. Megastigmus spp. were found in 29 of the native conifers of the genera Abies, Cedrus, Cupressus, Juniperus, Larix and Picea in 43 of the exotic conifer species introduced to Europe, in 28 species of Rosaceae (Amelanchier, Rosa and Sorbus) and in 9 species of Anacardiaceae (Pistacia and Schinus). Fifteen species develop in seeds of conifers whilst 6 infest the seeds of Angiosperms. Thirteen of the chalcid species are considered to be native. The other species were probably introduced from North America (7 species) and South Africa (one species) along with seeds. Chalcid specificity and evolutionary relationships with host species are discussed. Illustrated keys to males and females are presented, followed by a detailed description of species morphology, host range and distribution. A list of Megastigmus seed chalcids at risk of introduction from other world regions is provided, along with the host plants to be surveyed.