Rice Tungro virus eipidemics occur regularly in different regions in the Philippines. Whether this is due to climate change or other driving factors is not known as there is limited knowledge on this aspect either as regards the disease or the insect vector of the virus. This unavailability of data limits the development of a long term strategy to manage the disease especially during the current climate change upheavals that are threatening agricultural ecosystems. Survey techniques and forecasting models appear to be the tools needed to understand evolving disease dynamics in order to design appropriate control measures and avert potential disasters.

With the objectives of surveying ang mapping current geographical distribution of the disease and developing a prototype rice tungro virus simulation model, Arc GIS Ver. 9.2, a geographic information system (GIS) technology software to generate maps, CLIMEX software to predict potential distribution, and STELLA Version 9.02 modeling software to develop the model, were utilized.

Tungro virus disease is as widespread as it is destructive as ever in major rice growing areas in teh Philippines. It can be observed distinctly in one-month old rice plants and can occur as localized epidemic in many regions. It is destructive in poorly-managed farms owing evidently to the proliferation of the insect vectors int eh absence of control measures.

CLIMEX runs during the wet season using climate date from 1991-2002 showed high ecoclimatic index (≥18.4), indicating high suitability to rice tungro virus epidemics, in the Ilocos region, western parts of Central Luzon, Mindoro island, Panay Island, Negros Isalnd, Palawan and Zamboanga provinces.

GIS maps of rice tungro in Cansilayan, Murcia, Negros Occidental showed that disease spread in localized and intensification tended to be internal within foci of infection. During the period, the highest incidence recorded was 38 percent. Analysis utilizaing Vanderplank's compound interest disease model yielded an apparent infection rate of 0.697 per unit per week.

A prototype rice tungro simulation model, called VIRUSIM, was earlier constructed using the modelling language STELLA Version 9.1. this model was found wanting and has since been modified six (6) times using a higher version of the language, STELLA Version 9.02. The latest version is given the acronym rtvSim for r, rice, t, tungro, v, virus, Sim, simulation.

Hundreds of computer runs have since been done is a sensitivity analysis where different levels of temperature were used to determine the effect on behaviour of the developmental stages of the green leafhopper (GLH) insect vector. A user interface was constructed for easy sensitivity analysis runs. Higer influenced the GLH populations of 3rd, 4th, 5th instars, and adults resulting in greater number of infected hills and consequently higher percentage of rice tungro incidence.

An initial validation of rtvSim involved the comparison of the behaviour of the curves of rice tungro data from three field plots obtained over aperios of 35 days with data on temperature from a nearby weather station. Similar ranges of the temperature variable were inputted in the computer model run. A conclusion on the reliability of the model will have to be postponed pending additional validation experiments.  

Specific Objectives:
1. To survey current rice tungro virus disease occurrence in the Philippines;
2. To map the current geographical distribution of rice tungro virus disease in the Philippines
3. To map the potential geographical distribution of rice tungro virus epidemics in the Philippines under climate change; and,
4. To develop a prototype rice tungro virus simulation model