ダイズサヤタマバエの外部寄生蜂,Philomacroploea Pleuralis (Hymenoptera: Braconidae)の齢構成と寄生率

抄録

The occurrence of the soybean pod gall midge, Asphondylia sp. and its ectoparasitoid, Philomacroploea pleuralis was studied in Kagoshima Prefecture in 1951-52 and in Kanto district in 1956-57. These studies showed that there were 2 peaks of occurrence in the middle of June and the middle of September in Kagoshima, and 1 peak around the middle of September in the Kanto district. The parasitoid was considered to be one of the effective agents of control of the gall midge population, because of its relatively high percentage of parasitism in both the area. However, no detailed information is available on the biology of the parasitoid. The changes in the age structure observed in the present study revealed that P. pleuralis had at least 2 generations from June to November, and the parasitic activity of the wasp declined from August to September. The relationship between the density of the parasitoid and that of the soybean pod gall midge was not clear. The pattern of seasonal changes in the percentage parasitism observed in the period 1980-82 was similar to that in 1951-52, but the percentages were not as high as those recorded about 30 years ago. In recent years many paddy fields have been converted into soybean fields. The soybean pod gall midge has been noted to occur in such newly established soybean fields soon after the beginning of cultivation. It is remarkable that P. pleuralis was found in the present study to attack the host midge immediately after the invasion of the gall midge to the drained soybean fields. This finding suggests that P. pleuralis had been present somewhere near the soybean fields attacking hosts other than the soybean pod gall midge.