The egg parasitoids, Trichogramma japonicum and Telenomus dignus, seem to have doubtful impact on the regulation of rice yellow stem borer, Scirpophaga incertulas – It is time for a reality check

Abstract

The egg parasitoids, Trichogramma japonicum and Telenomus dignus, generally record a high rate of parasitism of egg masses, often 100%, but critical studies in India revealed that these, either alone or in combination, parasitized only up to 60% of the eggs in an egg mass, allowing the remaining 40% to hatch and cause potential damage. It is so because they could parasitize only those eggs that are laid on the upper surface and cannot reach out and parasitize eggs laid at the bottom layer. As a result of this inherent limitation resulting in partial parasitism of egg masses, these parasitoids, either by way of natural parasitism or artificial releases even in high numbers, seem to have a doubtful impact on the regulation of rice yellow stem borer (YSB), Scirpophaga incertulas. Tetrastichus schoenobii is also a common parasitoid of YSB, but it appears very late in the field and remains active only for a short period which greatly reduces its importance unless manipulated as suggested. It is time for a reality check and to be pragmatic in our approach in utilizing these parasitoids.