Trichogramma japonicum is periodically colonised in summer low-land rice (Oryza sativa) to biocontrol the yellow stem borer (Scirpophaga incertulas).

Abstract

A significant pest of low-land rice (Oryza sativa L.), yellow stem borer [Scirpophaga incertulas (Walker)]
reduces yield by 30–40%. Inundative discharges of the egg parasitoid Trichogramma japonicum Ashmead are
one of the biological control agents used to reduce yellow stem borer (YSB) populations and damage across
Asia. To suppress YSB in summer low-land rice, however, information on the timing and quantity of parasitoid
releases is missing. In order to standardise the timing and quantity of T. japonicum releases for efficient
biocontrol of YSB, an experiment was carried out in the summer of 2018 and 2019 at ICAR-National Institute
of Biotic Stress Management, Raipur, Chhattisgarh. Three distinct treatment schedules were used in the
experiment: T1 (four releases of T. japonicum at weekly intervals on the 7th, 14th, 21st, and 28th days after
planting (DAT); T2 (four releases of T. japonicum at weekly intervals on the 14th, 21st, 28th, and 35th DAT);
T3 (four releases of T. japonicum at weekly intervals on the 21st, 28th, 35th, and 42nd DAT); and T4, Control
(no release of wasps). In comparison to untreated control plots (T4), which had 16.8% dead heart and 3.4%
white ear in the summer of 2018, the treatment schedule (T2), which included four releases of T. japonicum
(@50,000 wasps/ha/release) at weekly intervals on the 14th, 21st, 28th, and 35th DAT of rice, significantly
reduced the symptoms of YSB-induced damage. Similarly, in the summer of 2019, the therapy (T2) reduced
white ear and dead heart by 46.15% and 43.35%, respectively, compared to the control. The higher grain output
in (T2) from 2018–19, or 12.74–20.18% over the seasons, correlated with the notable decrease in YSB-induced
damages. The findings imply that throughout the summer months in low-land rice, the (T2) augmentative
releases provide ecologically feasible bio-control of YSB.