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Parasitoids of Yellow Stemborer (YSB)

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1. The Egg parasitoids of yellow stem borer are Telenomus dignoides (Nixon), T. rowani Gahan, T. dignus Gahan, Tetrastichus schoenobii (Ferr.) and Trichogramma japonicum (Ashm.) are quite effective in controlling the pest population.
2. T. dignoides is the most frequent, widely distributed and effective parasitoid of all. The extent of cumulative egg mass parasitism due to all the egg parasitoids reported from different parts of India range from 4.0 to 97.2%.
3. Activity of T. schoenobii was observed towards end of the season parasitizing alone or in combination with other parasitoids. Super-parasitism was never observed in T. dignoides but T. japonicum exhibited it on a few occasions.
4. T. japonicum released @ 1 lakh/ha during kharif increased the extent of parasitism by 0.2 to 5.6%. Observations indicated that the three parasitoids have selective oviposition preferences and avoid multiple parasitism in an individual egg.
5. Studies at CRRI, Cuttack indicated that parasitism of egg masses increased when the artificial placement of eggs masses of stem borer continued in the rice field, especially during the scarcity of moth population. Collection of egg masses and putting them in bamboo cages cum perches encouraged the build up of parasitoid population.
6. During wet season egg mass wise parasitism ranged from 84.6 to 100% and egg wise parasitism from 28.0 to 74.7%. During dry season egg mass wise parasitism was up to 100% whereas egg wise parasitism ranged from 26.0 to 56.0%.
7. In general eggs of YSB laid towards late tillering or early reproductive stage of the crop are parasitized to lesser extent as the rice plants are older and borer eggs are laid towards lower part of the leaf or leaf sheath among the dense foliage.

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