Division of Entomology, Indian Agricultural Research Institute, New Delhi-110 012 (India).
*A part of approved Ph.D. thesis submitted by T. Venkatesan to the Post-graduate School, Indian Agricultural Research Institute, New Delhi (India).
The maggots of stem fly, Melanagromyza sojae (Zehnt.) cause extensive tunnelling in the pith region of the stem due to which the seedlings succumb, while growth and yield in grown up plants get significantly reduced. In order to quantify the loss in soybean yield and yield contributing characters due to stem tunnelling and to determine economic threshold level, the data on stem tunnelling, pod number, pod weight and grain yield were subjected to regression analysis. Significant negative correlation was obtained between the stem fly infestation and grain yield. The stem tunnelling ranging from 10.0 to 20.0 per cent per plant caused a loss of 24.83–33.96 per plant or a loss in pod weight 5.16–7.09 g or a grain yield loss of 2.75–3.81 g per plant. The linear and quadratic equations calculated for the variety Pusa-16 showed that for every 10 per cent increase in stem tunnelling, there was 1.65 to 2.74 g reduction in grain yield per plant, respectively. The economic injury levels were determined to be 6.40 and 11.23 per cent stem tunnelling with quadratic and linear form of relationship, respectively.
