Seed-infesting chalcids of the genus Megastigmus Dalman, 1820 (Hymenoptera: Torymidae) native and introduced to the West Palearctic region: taxonomy, host specificity and distribution

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Abstract
A total of 21 species (including one new to science) of Megastigmus seed chalcids are recognized in Europe, North Africa and Asia Minor. From 1977 to 2001, 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 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, Sorbus) and in nine species of Anacardiaceae (Pistacia, Schinus). Fifteen species develop in seeds of conifers whilst six infest the seeds of Angiosperms. Thirteen of the chalcid species are considered to be native. The other species were probably introduced from North America (seven 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.