Abstract
Parasitism of the two species of egg parasites of Nezara viridula, namely Asolcus mitsukurii and Telenomus nakagawai was the centre of the discussion based on the analysis of the data obtained from the field censuses mainly carried out at Asso in 1961 and 1962 for the successive generations of the host. In the first generation of the host, the egg masses parasitized by both species produced more A. mitsukurii significantly than T. nakagawai without hyperparasitism, but in the second one this tendency could not be detected. The mean size of egg masses parasitized by different species increased but the value of c.v. decreased in the order of A. mitsukurii, T. nakagawai and both species. Such a tendency was not observed in the second generation, because of the increase in the mean size of egg masses. These facts showed that interspecific interference in the first generation of the host occurred through more or less direct coactions of female parasites, but this was not the case in the second generation.
Measurement of the degree of interspecific association was made by using the COLE'S index of interspecific association and the results obtained were discussed by a plausible mechanism of interspecific interference brought about by fighting behaviour of the females of both species; A. mitsukurii wins over T. nakagawai by fighting. Percentage of parasitism of both species remarkably decreased in the second generation of the host as compared with that of the first generation. This was probably due to the poor synchronization of the parasites with the host eggs owing to the difference in the dispersal ability between host and parasites.
At Kogawa area where two species of Nezara are co-existing, T. nakagawai dominated A. mitsukurii, in contrast with the reversed case at Asso. This is possibly ascribed to the difference in the climatic conditions between the two areas. There could not be seen the severe interspecific interference in the first generation of the host as observed at Asso.
The possibility of biological control of Nezara population by liberation of parasites was proposed from these considerations.
