Relationship between phenological stages of boro rice and the stages of life cycle of yellow rice stem borer (Scirpophaga incertulas) in fields

Abstract

An experiment was carried out to evaluate the “Relationship between phenological stages of boro rice and the stages of life cycle of yellow rice stem borer (Scirpophaga incertulas) in fields” at the experimental stations of Porabari, Salna, Gazipur, adjacencent to Bangabandu Sheikh Mujibur Rahman Agricultural University, Gazipur and different laborites of Bangabandu Sheikh Mujibur Rahman Agricultural University and Environmental Biology and Biodiversity Laboratory (EBBL), Department of Zoology, University of Dhaka, during the boro season, November, 2010 to May, 2014. The results revealed that the plant height, number of total tillers, number of effective tillers, LAI, CGR, NAR and RGR significantly varied among the varieties at different phenological stages as well as the duration of different phenological stages differed significantly among the varieties. From the biological study of yellow rice stem borer (YSB), it was found that the duration of egg to larva, larva to pupa, pupa to adult and total life cycle of YSB were 6. ±0.5 days, 28.2 ± 0.60 days, 8.1± 0.44 days and 42.3±1.25 days respectively. From the coincidence of phenological stages of rice varieties and the stages of life cycle of YSB, it was observed that the adult YSB always appeared maximum and laid eggs at vegetative stage at the 4th week of February and eggs changed into larvae at the same phenological stage, larva changed into pupa at reproductive stage and pupa changed into adult at post reproductive stage of all rice varieties. After harvesting the rice varieties, the newly emerged adult eggs remained in the stubble of paddy fields. This coincidence of two biotic aspects (rice varieties and YSB) continued among the distinct phenological stage of rice and the specific life stage of YSB (S.incertulas ) in three different rice growing seasons (aus, aman and boro) in Bangladesh throughout the year . Mid-January transplanting time of rice varieties in boro season might be made a temporal favorable coincidence between the each life stages of YSB and the different phenological stages of rice varieties. From the nature of damage, it was found that the infested hills as well as infested tillers were maximum at preflowerng stage and minimum were in active tillering stage in all varieties. Considering the prevalence of appearing of optimum phenological stage of rice and the adult YSB arrival time, percentage of infestation as well as rice yield, the best time for transplanting rice seedling in boro season would be early or late January instead of mid- January. Moreover, the stubble ploughing and flooding the paddy fields after immediate harvesting reduced the percentage of infestation of YSB.