Pemodelan Fenologi Populasi Penggerek Batang Padi Kuning Scirpophaga incertulas (Walker) Berbasis Pengaruh Iklim

Abstract

West Java province is the highest of rice production area in Indonesia, contributing an average of national rice production about 17.4% in 2009 to 2012. Rice production can be maintained or enhanced if we have a great capability to protect rice from pests’ infestation. In 1995, the population of rice white stem borer (WSB) Scirpophaga innotata (Walker) decreased, while the population of the rice yellow stem borer (YSB) Scirpophaga incertulas (Walker) increased to 30%. Since 1995, YSB was more dominant than WSB, with population of more than 90%. Based on the report from Directorate of Food Crop Protection, some areas in the West Java in particular of North Coastal region has a total area of high annual infestation compared to other regions, reaching ± 10 to 12 thousand ha. High infestation of YSB is suspected as a result from transition of rice varieties. Furthermore, climatic might have strong influence on population dynamics of rice stem borer. Understanding relationship between climatic factors and life cycle and population dynamics of YSB is important for long- and short term management strategies, as control measures to reduce production and economic losses. This research utilized DYMEX software and aims to develop a population dynamic model of YSB and to assess model's ability to predict abundance and population peak of YSB under climate change scenario SRES A1FI and B1. Modeling the YSB requires two major components: climate parameter and lower developmental threshold temperatures (To) to describe life cycle of YSB from the egg, larva, pupa, and adult stages. DYMEX also describe development, mortality, transfer of individuals from one to the next life stages, fecundity and reproduction of YSB. The coefficient of determination (R2) of calibration models between predictions and observations showed a strong positive correlation of 0.72. Model validation could well predict the peak population, with R2 of 0.42. The simulations showed that the trend of population peaks occur at high rainfall i.e. in March to April, July to September, and November to December. The model predicted YSB population in the Sukamandi and Pusaka Negara reaches 3 generations per year, while in Kuningan 2 generations per year. Decrease in the population will affect the number generations of YSB in the three regions. Simulation models under climate change scenarios SRES A1FI and B1 showed differences in the sensitivities. Trend of YSB population is increasing in the regions Pusaka Negara and Kuningan and decreasing in region Sukamandi. Under changing climate, environment conditions in Pusaka Negara and Kuningan become more suitable for the proliferation YSB, allowing an increase in the number of generations per year. The level of model accuracy can still be improved by exploring more variables to include interactions between YSB and host plant (paddy) and the natural predators parasitism against the YSB. This makes model becomes more complex but may reflect better condition of YSB populations in the field. Further model improvement could be facilitated by be integrating DYMEX and CLIMEX software to determine the distribution of species in relation to climatic conditions. This models integration can simulate regional risks and determine whether a site could potentially be infested by YSB species. This study produces a model which is able to predict effect of climate on YSB populations and generate patterns that fit between the predictions and observations. The model produced good predictions on number of generations and population peaks under high and low rainfall intensities. These results show that DYMEX could be used as a tool for planning and managing YSB control under current and future climatic conditions.