The effect ofChito partellus(Swinhoe) on growth and yield of maize was investigated in two field experiments, using artificial infestation in cages. The first experiment consisted of five infestation levels, viz. 0, 15, 30, 45 and 60 eggs per plant. Plants were infested 3 weeks after emergence. The second experiment involved infestation on five occasions, viz. 2, 4, 6, 8 and 10 weeks after plant emergence, with a single infestation level of 30 eggs per plant. Results from both experiments indicated that whorl damage increased until 2 weeks after infestation, with minimal increases recorded at later stages. Levels and times of infestation were both non-linearly related to yield loss, the slope being positive for levels and negative for time of infestation. The level of whorl damage 2 weeks after infestation proved reliable for the estimation of yield losses. The economic threshold was determined as 40% plants with visible whorl damage.