Estimation of economic injury level (EIL) of cotton bollworm Helicoverpa armigera Hb. (Lep., Noctuidae) on cotton

Economic Injury Level (EIL) of cotton bollworm Helicoverpa armigera Hb. was evaluated onSahel variety in Gorgan, Iran during 1999-2000. Infestation levels of 0, 2, 3, 4, 6 and 8 neonate larvae per 100 reproductive organs were studied in three generations of the pest by releasing them on cotton plants in the field. Statistically significant differences between treatments were observed in all generations. In the first generation, infestation level of 8%, in the second and third gernerations, infestation levels of 4, 6 and 8% caused significant reduction in yield (p0.05). Reduction yields for infestation level of 8% in the first-generation was 13.94%, in the second generation the infestation levels of 4, 6 and 8% were 9.8, 16.77 and 22% respectively, and in the same infestation levels in thethird generation were 8.25, 14.85 and 19.17%. Linear regression between the cotton yield and pestdensity was obtained in different generations. Considering the total cost of chemical cont rol operations and cost of yield, the economic injury level of the pest for the first, second and third generations were 1.19, 0.66 and 0.79 neonate larvae per 100 reproductive organs respectively, which is equal to 22.25, 15.77 and 21.33 neonate larvae per 100 cotton plants, respectively.