Abstract
Barnyard grass (var. oryzicola) showed no apparent damage in paddy fields where hopperburn occurred by a large number of N. lugens. The causes of barnyard grass resistance to this insect and the insect-host interrelations of three species of planthoppres (N. lugens, L. striatellus and S. furcifera) between rice plant and barnyard grass were studied. Nymphs of N. lugens could not grow by feeding barnyard grass without regard to its leaf stage and died within a few days, whereas thoes grew well by feeding rice plant. On the contrary, nymphs of the other two species of planthoppres grew up normally to the adult stage even on barnyard grass as well as on rice plant. Extract of barnyard grass showed an antifeedant effect against N. lugens when it was added to a sucrose solution. It seems that resistance of barnyerd grass to this insect is due mainly to the presence of antifeedant(s).
