Characteristics of three cotton varieties and their impact on feeding and growth of cotton armyworm

This study investigated morphological and biochemical characteristics of CB9, CB10 and SR05 cotton varieties and observed their effect on feeding and growth of cotton armyworm Spodoptera litura. Morphological characters of plant architecture, branching, color, hairiness, trichome density and boll size indicated that CB9 is a bushy, well developed, branched, light bronze colored and hairy variety with number of trichomes 193/cm(2) and boll weight 5.5-6.0 g/boll. Both CB9 and CB10 bear normal leaves and spherical bolls whereas SR05 has well-ventilated branching, okra shaped and ventrally arranged light bronze colored leaves and oval bolls ranging 4.0-4.5 g/boll. Biochemical analysis indicated significant differences in starch and protein contents, which range 11.4-21.3 and 17.5-30.6%, respectively. The lowest percentages of starch and protein were found in SR05 and CB9, respectively. Cotton varieties showed significant effects on second, third, fourth and fifth instar larval weight and they attained the highest weights (22.7, 133.8, 168.2 and 1190.2 mg, respectively) when fed SR05. Larvae and moths fed SR05 also showed the significantly highest cocoon, exuviae, and adult male and female weights (434.5, 19.2, 161.3 and 232.4 mg, respectively). The cotton armyworm showed the significantly highest growth index (1.5) as well as lowest feeding index (0.05) on SR05. Results of this study indicated that SR05 is suitable for larval feeding and development, and suggest that this variety is least suitable for cotton growers in areas where S. litura is a major pest.