Effect of Rice Armyworm Mythimna Separata (Walker) on Grain Yield of Rice

A survey conducted in Maligaya, Nueva Ecija, Philippines, showed that farmers (n=100) consider the armyworm (AW) Mythimna separata (Walker) one of the most important insect pests of rice during the dry season. The AW hosts include sugar-cane, sorghum, maize, bamboo, and some grasses. At night, AW larvae are actively feeding and cutting rice panicle rachis and stems (see figure). During the day, they are found at the base of tillers. The occurrence of AW forces some farmers to harvest earlier than scheduled for fear that panicles will be lost. This study quantified the effect of AW on grain yield by comparing healthy hills with hills affected by AW. This information may be used to estimate yield reduction caused by AW.