Multiple releases of Trichogramma japonicum Ashmead for biocontrol of rice yellow stem borer, Scirpophaga incertulas (Walker)

Yellow stem borer (YSB), Scirpophaga incertulas (Walker) is considered as major pest of rice. An egg parasitoid, Trichogramma, is used for management of Lepidoptera pests of rice across the world. In order to optimize the time and number of releases of Trichogramma japonicum three different schedules of releases of T. japonicum were evaluated to manage YSB during rainy season 2017 and 2018 (June to October) under low land rice. Each schedule consisted of multiple releases of wasps for four times at weekly interval (50,000 wasps/ha/release × four releases or 500 wasps/100 m2/release × four releases). The statistical analyses of two seasons data revealed that four releases of T. japonicum at weekly interval on the 32nd, 39th, 46th and 53rd day after transplanting of rice had reduced the damage symptoms caused by YSB by 52.8% dead heart (2.51%) and 66.1% white ear (0.62%) when compared to control plots (5.32% dead heart; 1.83% white ear). The results suggest that the time-specific multiple releases of T. japonicum @ 50,000 wasps/ha/release × four releases can be the useful to attain biocontrol of YSB. T1: Four split releases of T. japonicum @ 50,000 wasps/ha × 4 releases, at weekly intervals on the 25th, 32nd, 39th and 46th day after transplanting (DAT); T2: Four split releases of T. japonicum at weekly intervals on the 32nd, 39th, 46th and 53rd DAT; T3: Four split releases of T. japonicum at weekly intervals on the 39th, 46th, 53rd and 60th DAT; T4: Untreated control. [Display omitted] •Yellow stem borer, Scirpophaga incertulas is a predominant borer pest in Asian countries to cause 30–40% yield loss.•Trichogramma japonicum is a potential biocontrol agent of yellow stem borer.•Time and number of releases of wasps (50,000 wasps/ha/release × 4 releases) optimized.•Four releases of wasps at weekly interval, begin in the 32nd day after transplanting.•Multiple releases of wasps is potential for bio-control of yellow stem borer.