DETERMINATION OF ECONOMIC INJURY LEVEL FOR THE TOBACCO CAPSULE BORER, HELICOVERPA ARMIGERA (HUBNER) ON FCV TOBACCO

Abstract

Tobacco capsule borer Helicoverpa armigera (Hubner) is one of the major pests of tobacco. The damage potential of the pest to flue-cured Virginia (FCV) tobacco seed and economic injury level of H. armigera larva were worked out. There was a significant reduction in pod damage at various levels of larval infestation as compared to completely protected plots. The capsule damage ranged from zero in the completely protected plant to 37.82% where five larvae per plant were released. The correlation between number of larvae per plant and the per cent capsule damage was positive and significant (r=0.98). The results also revealed that the reduction in seed weight with increased larval density. The seed weight in different treatments ranged from 12.26 to 21.37 g/plant. The correlation between the number of larvae per plant and the seed weight was negative and significant (r = -0.85). Statistical analysis revealed that the correlation between larval population and reduction in seed weight per plant was positive and significant (r = 0.85). Regression analysis and the computation of EIL showed that the per cent reduction in yield per incremental larva over control was 10.52. Reduction in seed yield per incremental larva was 1.43 g/plant. The seed capsules damaged per incremental larvae was 7.18%. On an average a single larva per panicle reduced seed yield to an extent of 100 kg/ha in 2011 and 116 kg/ha in 2012 crop seasons, respectively. The ratio of the value of the yield (price of tobacco seed sold for oil extraction) to the cost of insecticide application at one third instar larva per panicle was 0.98 and 0.96 in 2011 and 2012 seasons, respectively. Based on the damage, yield relationship and cost of protection, the EIL for H. armigera was determined as one third instar larva/panicle.