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: Acrididae), a bioassay using sucrose-impregnated filter paper as the feeding substrate and a feeding assay on barley lines with different contents of gramine were conducted. Gramine deterred feeding of the locust dose dependently in a range of 50-500 μg/150 mg paper in the filter paper assay. On the whole, there was a good correlation between gramine content in mature plants and feeding deterrence against L. Migratoria; barley lines with gramine content of more than 100 μg/g deterred feeding of the locust, while those with less than 50 μg/g of gramine were susceptible to feeding by the locust. However, when the developmental changes of gramine content in barley and 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 gramine 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.