Abstract
Various numbers of newly hatched larvae i.e., 5, 10, 30, 50, 100 and 200 were placed artificially on rice plants, and survival rates of early, middle and late instar larvae were investigated. Survival rates of the early instar larvae were low in all group sizes of the first generation and in the smaller group sizes of the second generation. Survival rates of larvae in the larger group sizes of the second generation and of the third generation were high. The mortality was density-dependent in the first generation, whereas it showed an inverse relation in the second and the third generations. Survival rates of the middle instar larvae were always high irrespective of the group size. The mortality of the late instar larvae was high in all the generations, and the effect was density-dependent. Such a high mortality rate of older larvae seems to be related to the destruction of the stem by larval feeding.
