Life tables of the spotted stem borer Chilo partellus (Swinhoe) on maize cultivars

Forty-eight lifetables were constructed for Chilo partellus (Swinhoe) on six maize cultivars viz., DHM 117, DHM 121, Madhuri sweet corn, Priya sweet corn, Amber pop corn and 30V92. In each season of kharif and rabi 2014–15 and 2015–16 two generations were studied. The survivorship curves drawn indicated that the mortality rate was in the early larval stage. Generation survival declined from first generation in first crop during kharif 2014 to second generation in fourth crop during rabi 2015–16 in all maize cultivars (0.33 to 0.23 in DHM 117, 0.39 to 0.22 in DHM 121, 0.37 to 0.24 in Madhuri, 0.38 to 0.25 in Priya, 0.32 to 0.21 in Amber and 0.43 to 0.28 in 30V92). The trend index was positive (>1) and varied in all the generations. Key factor analysis revealed that the major mortality factors are the larval parasitoids particularly Cotesia flavipes (21.60 to 47.00%) and unknown causes during early and middle larval stages. Density dependant mortality was observed in all the cultivars except mortality due to diseases in middle stage larvae in DHM 117 and pupal mortality due to Tetrastichus howardi in Amber popcorn which exhibited inverse density dependence. The highest mean values of generation survival (0.38) and the trend index (40.2) were obtained on the 30V92 cultivar and the least values for generation survival (0.27) and the trend index (25.2) being with the cultivar Amber popcorn.