Author(s): A. SINGHA AND S. CHATTERJEE

Abstract: An investigation was conducted during kharif 2008 in West Bengal, India, to study the population dynamics of insect pests and their natural enemies in rice seed bed. A total of 199.50 pests belonging to 13 different types was recorded, of which rice thrips (Baliothrips biformis [Stenchaetothrips biformis]) and grass hopper (Hieroglyphus banian) were dominant. The total population load of all the three pests was highest during the first week of July (53.00) and it gradually declined with time, which may be due to the progressive build up of natural enemies. In total, 113.67 predators belonging to 12 different groups were recorded. Of these, the populations of dominant predators, i.e. lynx spider (Oxyopes sp.), damsel fly (Agriocnemus pygmaea) and water bag (Mesovelia vittigera) were 27.67, 19.33 and 17.50, respectively. Predator population was highest during third week of July (34.67). Telenomus rowani (10.50) and Tetrastichus schoenobii (11.33) were dominant parasites. Total parasite population was maximum (10.00) during the fourth week of July. The population ratio of pest:predator, pest:parasite and pest:natural enemy was 1.76:1.00, 7.44:1.00 and 1.00:1.21, respectively.

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