The effect of infestation by helicoverpa armigera (Hbn.) lepidoptera: noctuidae at different stages of cotton growth on yield and quality

The African bollworm, Helicoverpa armigera (Hbn.) {Lepidoptera: Noctuidae}, is a destructive and polyphagous insect pest with a wide range of distribution. In Sudan, the species annually inflects serious damage to cotton and entails several insecticidal applications which are costly both economically and environmentally. The effects of infestation caused by H. armigera at different stages of cotton growth on yield and quality were studied in order to rationalize the use of insecticides and reduce the cost of cotton production. Natural and artificial infestations were conducted in Gezira Research Farm (14 deg 24' N, 33 deg 29' E, 407 m above sea level) in field and cage experiments in 1997/98 and 1998/99 seasons. The laboratory culture needed for the artificial infestation was initiated by field collected larvae reared on artificial diet. The level of infestation used was 33.3 larvae per 100 plants and this was attained by depositing one laboratory-reared 2nd instar larva on each plant hole which contained three cotton plants. In the field, the artificial infestation in the first season (1997/98) resulted is a damage of 17% in buds, 34.6% in flowers and 11% in bolls and the natural infestation resulted in a damage of 1.7% in buds, 7.6% in flowers and 1.2% in bolls compared to both control treatments, i.e. infestation free, in which the egges of H. armigers were removed each 48 hours, and the conventionally sprayed which received three chemical sprays {Larvin (Thodicarb) 80% DF in October and Endosulfan 50% EC in November and December}. While in the second season (1998/99) the artificial infestation resulted in a damage of 15.2% in buds, 35.2% in flowers and 15.3% in bolls and the natural infestation caused a gamage of 3.6% in buds, 13.3% in flowers and 2.7% in bolls compared to the control treatments anddd here the conventionally sprayed treatment received only two sprays (Endosulfan 50% EC in November and December). In the cage, during 1998/99 season the artificial infestation caused a damage of 33.3% in buds, 57.1% in flowers and 18.8% in bolls compared to the control treatment which was infestation free. The cotton yield data which were statisticlly analyzed revealed the damage caused by H. armigera during the pre-flowering and flowering stages up to 105 days from seedling emergence could be compensated for by the plant. However, the damage resulted from infestation occurring after the initiation of the bolling stage was not compensated for and caused significant reduction in yield (P 0.05). Detailed laboratory fibre test (Fibre, spinning and stickiness testing laboratory (FS & STL). Showed that; if the partially damaged open-bolls are excluded, the infestation by H. armigera at any stage of cotton growth has no effects on the fibre quality attributes