The Control Threshold Density of the Tobacco Cutworm Spodoptera litura (Lepidoptera : Noctuidae) on Eggplants and Sweet Peppers in Vinyl-houses

The control threshold density of the tabacco cutworm Spodoptera litura was determined separately in eggplants and sweet peppers cultivated in vinyl-houses during the winter. A vinyl-house was divided into small plots and different numbers of egg masses of S. litura were artificially placed on the plants in each plot. A linear relationship was found between the yields of total fruits and marketable fruits, and an index of plant injury, F, which represents the total amount of palnt material consumed by larvae. Assuming 10% of the maximum yield as the critical level of yield loss, the tolerable injury thresholds in terms of this index were calculated as 43 and 49 for the marketable fruit yield of eggplants and sweet peppers, respectively. These values corresponded to 4.6 and 15.4 individuals of S. litura hatchlings per m2, or 0.8 and 2.6 egg masses per 100m2, respectively.