Abstract: A laboratory evaluation of food consumption and utilization by larvaeof Mythimna separata (Walker) under different rearing densities (1, 15, 30larvae/jar) was made from the beginning of the fifth and sixth instar of larvae to the prepupal stage on the corn seedling. The food consumption, whether on daily or total basis increased with the larval density increased indicating that crowding may stimulate food intake of the larvae and hence enhance their damage on crops. This trend is also conspicuous in the amount of voided faeces. The growth, as measured by daily larval fresh weight was the highest at the density of 1 larva/jar, followed by 15 and 30 larvae/jar, due to the lower efficiency of approximate igestibility (AD) and lower efficiency in converting ingested food into body matter (ECI) in the higher rearing densities. Presumably, the lower AD and ECI should be the bases of the major reasons for the smaller size of M. Separata in the crowded conditions. It should, however be noted that all these difference would become insignificant as the period of larvae separating from the given rearing density become longer.

Key words: Mythirnna separata, larval rearing density, food consumption, food utilization