ダイズサヤタマバエによるダイズ被害粒率の評価時期

抄録

The soybean pod gall midge, Asphondylia sp. has been known as a serious pest of soybean particularly in south-western Japan. However, some aspects of the life history and host plant range of the species still remain unclear. In order to clarify the life history and establish a control method against the gall midge, it is necessary to evaluate the rate of infested beans through an investigation on the age structure of the species in association with the developmental stages of the host pods. The rate of infested beans was often underestimated owing to the following reasons: (i) overlooking the tiny midge eggs or immature larvae in dissection; (ii) successive invasion of adult midges into soybean fields; (iii) earlier fall of infested pods after emergence of adults; (iv) fall of puparia out of the infested pods; (v) emergence of parasitoid wasps which prevents recognition of the emergence holes of the gall midge. In this paper, the developmental stages of the host pods are expressed in terms of the percentage of young (less than 20 mm in length) to the total pods. The rate of infested beans was more accurately evaluated by sampling the host pods with 1 to 7 percent young pods for the two cultivars, "Wasemidori" and "Akisengoku", and 5 to 30 for "Kogane".