1. A discussion is brought up on the interrelation between two species of egg parasite of the rice stem borer, Trichogramma japonicum ASHMEAD and Phanurus beneficiens ZEHNTER, which inhabit together in a rice field in Matue district.
2. It is frequently observed that an egg mass is simultaneously parasitized by both species, as tabulated in Table I. It is concluded from the agreement between the observed frequency of parasitized egg masses by both species and the calculated frequency based upon probability, that the egg deposition of one species parasite to an egg mass is not influenced by another species even if an egg mass of the borer has already been parasitized by another.
3. It seems that both species have no ability of discrimination between healthy and parasitized egg and P. beneficiens is killed by T. japonicum when multiple parasitism occurs between them.
This is the reason that the number of P. beneficiens in the egg mass parasitized by both species is frequently less than that in the egg mass parasitized by P. beneficiens alone, as represented in Figure 1.
4. Multiple parasitism, however, did not occur so frequently, because the number of host eggs parasitized by T. japonicum in each egg mass is usually small comparing to the total numder of eggs composing an egg mass, and great number of them remains to be available for parasitization.
Therefore, in spite of the population of P. beneficiens is checked by that of T. japonicum both parasites can coexist in the same place, in the same time.