Seasonal occurrence of the rice gall midge orseolia oryzae wood mason and parasitism by its parasitoids platygaster oryzae cameron and platygaster foersteri gahan hymenoptera platygastridae in the paddy field of thailand
Kobayashi, M.; Kadkao, S.
Japanese Journal of Entomology 57(4): 901-916
Seasonal occurrence of immature stages from egg to pupa of the rice gall midge Orseolia oryzae was investigated in Chiang Rai Province of northern Thailand during 1973-1975, and life tablets were constructed for evaluating the impact of two egg-larval parasitoides, Platygaster oryzae and P. foersteri on the host population. The rice gall midge was estimated to complete two generations in the paddy field when the eggs of the first generation were deposited before mid-August, because newly hatched larvae of the second generation, as observed in 1973 and 1974, could enter the growing points of the rice plants before beginning to form young ears in mid-September. P. oryzae showed a density-dependent response to the host populations. On the other hand, P. foresteri slightly responded to increase in the host density. Parasitism by P. oryzae possibly contributed to the generation mortality when percentage parasitism was as high as 65% or so in 1974. However, parasitism by P. foersteri was too low to influence host population density. Key factor for population fluctuation of O. oryzae was supposed to be the mortality acting on the newly hatched larvae before entering the growing points of the rice plants or on female adults before depositing their eggs, by VARLEY and GRADWELL's (1960) graphic method.