The transitions of occurrence and control of major rice insect pests in Tokai district

Abstract

The transitions of occurrence and control of major insect pests of rice in Tokai district were reviewed. Data were obtained from the annual reports of Prefectural Forecasting Offices in Aichi, Gifu and Mie.
Annual catches of 5 major insect pests by the light traps in Agricultural Experiment Stations were compared for 29 years from 1947 to 1975. The major pests were as follows: the rice stem borer, Chilo suppressalis Walker, the green rice leafhopper, Nephotettix cincticeps Uhler, the smaller brown planthopper, Laodelphax striatellus Fallén, the white backed planthopper, Sogatella furcifera Horváth, and the brown planthopper, Nilaparvata lugens Stål. The trend curves of the occurrence of the pests were given by fitting the logarithmic numbers of the annual catches to the quadratic exponential formulae. Decreasing trends were observed in the recent years for all pests except for N. cincticeps in Mie.
The trend curves were also examined for the percentage acreage in the infested paddy fields and of the paddy fields treated with insecticides. Seven minor pests were added to the major pests in this examination. Some different trends were observed between the pests and between the localities. Infested areas by S. furcifera, the plant bugs, the rice plant skipper, Parnara guttata Bremer et Grey, and the rice leaf beetle, Oulema oryzae Kuwayama, increased in recent years in Aichi and Gifu, while almost all pests except for the plant bugs decreased in Mie. The acreage of the paddy fields treated with insecticides against all major pests increased gradually in both Aichi and Gifu. While in Mie, the acreage decreased except for N. cincticeps and the plant bugs. Those differences in the trend between the localities are considered to be related to the timing of the transplantation of rice seedlings and of the harvest.