Abstract
Emmalocera sp. (Lepidoptera: Pyralidae) is a monophagous stem borer of the barnyard grass involving two varieties, Echinochloa oryzicola and E. crus-galli var. crus-galli, which grow in paddy fields. Factors responsible for the onset of diapause in Emmalocera sp. were investigated with reference to food quality, i.e. varieties and growth stage of the host plant. Percentages of larvae which underwent diapause differed between varieties and plant ages of Echinochloa. The type of photo response of Emmalocera sp. was long-day type. Critical day-length located between 12 and 15hr. When larvae were reared under different day-lengths around the critical one, most of the larvae developed pupation on young host plants, while those on the old ones underwent diapause. The conversion stage from vegetative to reproductive phase differed between the varieties, i.e. 8-11th plant age in E. crus-galli var. crus-galli, 10-13th in E. oryzicola. Consequently diapause was induced earlier in the larvae developed on the former than the latter at the critical day-length. It was discussed between the number of generations of Emmalocera sp. in the paddy fields and two barnyard grass varieties.
