Egg Mass Density Dependent Parasitoids of Rice Yellow Stem Borer, Scirpophaga incertulas (Walker) (Lepidoptera: Pyralidae)

Rice, (Oryza sativa L.), is liable to infestation with several insect pests, from which the rice stem borer, Scirpophaga incertulas (Walker) (Lepidoptera: Pyralidae) is one of the most destructive and widely distributed throughout the india. To determine the extent of parasitization of yellow stemborer egg masses, the egg masses were randomly collected at weekly intervals depending on the availability from rice fields, and brought to the laboratory for collection of emerging parasites. The per cent egg parasitism was calculated based on the emergence of stem borer larvae or adult parasitoids. We found three species of hymenopterous parasitoids-Tetrasticus schoenobii, Telenomus spp., and Trichogramma japonicum from the observations of three consecutive experimental years. Among three, T. Shoenobii was predominant and remained active for the longer period as compared to Telenomus sp. and T. Japonicum. In the present study peak activity of T. Shoenobii (73 % in 2015-16; 72.67 in 2016-17 & 77.33 % in 2017-18) was found during first week of September, when the stem borer egg mass density was high (1.6 – 5.3 /sq.mt). The yellow stem borer egg parasitoid population followed a linear trend in relation to the availability of the YSB egg masses. Peak activity of Tetrastichus was noted when the egg mass density was high during first week of september, and the Tetrastichus activity was declined with the decrease in stem borer egg mass density.