Natural Mortality of Helicoverpa armigera (Hübner) Eggs in the Cotton Ecosystem

Field studies were conducted during the cotton crop seasons in 2003 and 2004 at CCS Haryana Agricultural University, Hisar, to identify mortality factors in the egg stage of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in the insecticide-free cotton fields to gain an insight into the role of these factors in causing egg specific mortality. Eggs were collected from cotton fields on different dates during September-November and brought to the laboratory for determining egg viability and level of parasitism. Similarly, plant parts bearing eggs in the field were tagged on different dates and observed daily to assess egg loss. The correlation of egg loss with various abiotic factors was determined. The mean viability of field collected eggs was 75% and 89% during 2003 and 2004, respectively (pooled mean egg viability of 82%). It was 51.34-66.55 (Mean: 59.72) % in the case of eggs deposited in the field by the laboratory-reared females. Eggs were parasitized by Trichogramma chilonis Ishii during September-October and mean parasitization was 25 and only 1-2% during 2003 and 2004, respectively. There was a positive correlation of % egg loss with wind velocity and rainfall as evident for multiple correlation coefficient values, i.e. 0.92 and 0.60 for 2003 and 2004, respectively. A partial ecological life table constructed for egg stage indicated that 23-44% mortality occurs at this stage. Important factors responsible for egg mortality/loss were identified as T. chilonis, inviability, rain, wind and unexplained mortality.