THE EFFECT OF RELATIVE HUMIDITY AND CULTURAL PRACTICES ON Tirathaba rufivena (WALKER, 1861) (LEPIDOPTERA: PYRALIDAE) POPULATION IN OIL PALM PLANTATION Rosina Baadu 1 , Zubaidah Yusop 1,3 , and Yahutazi Chik 2,3 * 1 Faculty of Plantation and Agrotechnology, Universiti Teknologi MARA Cawangan Sarawak, Samarahan Campus, 94600 Kota Samarahan, Sarawak, Malaysia 2 Crop Protection and Research Unit, Faculty of Plantation and Agrotechnology, Universiti Teknologi MARA Cawangan Sarawak, Mukah Campus, 96400 Mukah, Sarawak, Malaysia 3 Natural Product Research and Development Centre (NPRDC) UiTM Sarawak, Samarahan Campus, 94600 Kota Samarahan, Sarawak, Malaysia *Corresponding author: yahutazi@sarawak.uitm.edu.my ABSTRACT Tirathaba rufivena is one of major insect pests of oil palm industry in Sarawak especially oil palm planted at peat soil. It causes significant losses to Fresh Fruit Bunch (FFB) yield of oil palm if it reaches outbreak level. Therefore, there was a concern over the population of T. rufivena and its relationship with relative humidity (RH). A case study was carried out to identify the effects of relative humidity on the population of T. rufivena. This study was conducted at Saribas Estate 1, Pusa, Betong District in Sarawak within eight weeks by using Complete Randomised Design (CRD) with two treatments (maintenance and less maintenance area) and six replications. Light traps fitted with 18w bulb were used to collect the T. rufivena population while digital psychrometer XINTEST Model HT-86 was used to record RH level. The result showed the highest mean number of infested bunches was found at less maintenance area (n=6, M=15, SD=13.78) than maintenance area (n=6, M=13, SD=10.62), t (10) = -0.28, p =0.78. Furthermore, a simple correlation analysis was carried out and the result revealed that there was a weak, positive correlation between a number of T. rufivena and relative humidity in the maintenance area, r = .24, n = 48, p = 0.11 while, in less maintenance area, there was a medium positive interaction between population of T. rufivena and relative humidity, r = .40, n = 48, p = 0.01. The results indicated that, implementation of cultural practice in maintenance area and census as an early detection of the infestation level method helps in reducing the pest outbreak. Therefore, a comprehensive data collection is needed especially on the depth of peat soil in the area with the highest infestation level of T. rufivena to give more comprehensive information on the ecological aspect this insect pest. Keywords: Oil palm, Pyralidae, Tirathaba rufivena, relative humidity, peat soil ABSTRAK Tirathaba rufivena merupakan salah satu daripada serangga perosak utama di dalam industri kelapa sawit di Sarawak terutamanya kelapa sawit yang ditanam di tanah gambut. Ia menyebabkan kerugian besar kepada hasil Tandan Buah Segar (FFB) kelapa sawit sekiranya