Domestication of wheats (Gramineae) and their susceptibility to herbivory by Sitodiplosis mosellana (Diptera : Cecidomyiidae)

In field and laboratory tests the wheat midge, Sitodiplosis mosellana (Gehi n). oviposited and developed on all 43 accessions of 17 species of diploid, tetraploid, and hexaploid wheats, Triticum L. spp. Ancestral diploid wild wheats had the lowest infestations among species in the genus, and two hexa ploid species, Triticum sphaerococcum Percival and Triticum zhukovskvi Men. and Er., were more heavily infested than common wheat, Triticum zhukovskyi . In five lineages recognized in the genus, infestation increased in associ ation with domestication, although not always in a continuous way. The leve l of infestation was not related to seed size or the number of seeds in spi kes. Wheat species with free-threshing seeds and compact spikes were more i nfested by larvae than ancestral wheat species with less compact spikes and glumes that were either affixed to or pressed tightly against the seed. An association between glume tightness and spike compactness may explain the positive correlation between susceptibility and spike compactness. Domestic ation increased the susceptibility of crop wheats to wheat midge, possibly because the free-threshing trait affects the suitability of the glume-seed interface for oviposition and establishment of larvae on the seeds. The anc estral cultivated wheats, Triticum spelta L. and Triticum dicoccoides Korn. , are promising sources of resistance to wheat midge because they have the same genomes as modern wheats and relatively low susceptibility. One free-t hreshing accession of Triticum dicoccum Schrank had relatively low suscepti bility to wheat midge and may provide a source of resistance.