SEASONAL DYNAMICS AND RELATIVE A BUNDANCE OF EGG PARASITOIDS OF YELLOW STEM BORER, SCIRPOPHAGA INCERTULAS (WALKER) IN RICEAND IMPACT OF WEATHER FACTORS

摘要

The yellow stem borer is a key pest in rice and integrated pest management tactics for its management involve conservation of its natural enemies, viz. three hymenopteran egg parasitoids, Tetrastichus schoenobii Ferriere, Telenomus dignus (Gahan) andTrichogramma japonicum Ashmead. Studies conducted for three years (kharif seasons of 2010-2012) to understand the seasonal dynamics of the parasitoids and variations in natural parasitisation caused by each revealed that egg parasitisation started in 37th SMW and attained a peak (98.4%) by the 39* SMW. In the initial weeks, it was dominated mainly by T. dignus followed by T. japonicum and T. schoenobii. However, after the 39th SMW, T. schoenobii took over and recorded highest parasitization consistentlytill the end of the study (44°* SMW). The number of egg masses parasitized by a single genus were higher (63.9%) compared to those parasitized by more than one genus (36.1%). Maximum parasitisation, by T. schoenobii, T. dignus and T. japonicum were found to be 54.5,47.1 and 27.3 percent respectively. Among egg masses parasitized by more than one genus, T. schoenobii and T. dignus together parasitized a maximum of 35.3 per cent egg masses. T. schoenobii, T. dignus and T. japonicum together parasitizeda maximum of 7.7 per cent egg masses. Correlating parasitoid populations with weather factors revealed that among the three parasitoids, only T. japonicum was found to be significantly influenced by weather factors, while T. schoenobii and T. dignuswerenot.