Role of gramine in the feeding deterrence of barley against the migratory locust, Locusta migratoria (Orthoptera : Acrididae)

To examine whether gramine has an important role in the feeding deterrence of barley against the migratory locust, Locusta migratoria (Orthoptera: Acr ididae), a bioassay using sucrose-impregnated filter paper as the feeding s ubstrate and a feeding assay on barley lines with different contents of gra mine were conducted. Gramine deterred feeding of the locust dose dependentl y in a range of 50-500 mu g/150 mg paper in the filter paper assay. On the whole, there was a good correlation between gramine content in mature plant s and feeding deterrence against L. migratoria; barley lines with gramine c ontent of more than 100 mu g/g deterred feeding of the locust, while those with less than 50 mu g/g of gramine were susceptible to feeding by the locu st. However, when the developmental changes of gramine content in barley an d the changes of feeding deterrence against the locust were investigated, a barley line was found in which the young plant was susceptible to feeding by the locust despite a high gramine content. Therefore, the level of grami ne alone cannot account for the deterrence of barley against the migratory locust. The feeding deterrence of barley against L. migratoria must be due to multiple feeding deterrents, one of which is gramine.