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

Field studies were conducted during the cotton crop seasons in ۲۰۰۳ and ۲۰۰۴ 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 ۷۵% and ۸۹% during ۲۰۰۳ and ۲۰۰۴, respectively (pooled mean egg viability of ۸۲%). It was ۵۱.۳۴-۶۶.۵۵ (Mean: ۵۹.۷۲) % 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 ۲۵ and only ۱-۲% during ۲۰۰۳ and ۲۰۰۴, respectively. There was a positive correlation of % egg loss with wind velocity and rainfall as evident for multiple correlation coefficient values, i.e. ۰.۹۲ and ۰.۶۰ for ۲۰۰۳ and ۲۰۰۴, respectively. A partial ecological life table constructed for egg stage indicated that ۲۳-۴۴% mortality occurs at this stage. Important factors responsible for egg mortality/loss were identified as T. chilonis, inviability, rain, wind and unexplained mortality.

Keywords:

Cotton , Egg mortality , Helicoverpa armigera , Lepidoptera , Noctuidae , Parasitization , Trichogramma chilonis