RICE INSECT PEST AND ITS INTERACTION WITH NATURAL ENEMIES Badrulhadza, A.*, Nik Mohd Noor, N. S.**, and Saad, A.* *Rice and Industrial Crop Research Centre, MARDI Seberang Perai, Penang, MALAYSIA **Rice and Industrial Crop Research Centre, MARDI Alor Setar, Kedah, MALAYSIA INTRODUCTION Currently, insect pests are becoming important constraints to the high yielding and large scale rice production. Estimation of annual crop loss due to rice insect pests might be worsen in later years if or when major pest outbreaks occur. About 159 insect pests have being recorded on rice in Malaysia (Yunus, 1984) from sowing right up to the harvesting stage. Out of that, about 20 species have major significance. Large numbers of predatory and parasitic natural enemies of rice insect pest are present in Malaysia (Yasumatsu & Tan, 1981). Under normal circumstances, the populations of natural enemies are high enough to suppress insect pests population. However, the indiscriminate use of pesticides had limit the full exploitation of these potential biological control agents. Aims of the study are to report the insect pest diversity in the rice field and their interaction between the natural enemies. The study also compares the population of insect pest and natural enemies between rice field with pesticide usage and without pesticide usage. MATERIALS & METHODS Trial A (Insect pest & natural enemies study) – IPM Plot, Bumbong Lima, Seberang Perai Utara. Trial B (Comparison study of the insect pest and natural enemies population between rice field with pesticide usage and without pesticide usage) – Parit 11, Pasir Panjang, PBLS. Both studies were conducted during off-season 2004 and main season 2004/05. Samplings were carried out from 10 randomly selected hills across each field using 20 cm x 20 cm quadrate. Samples obtained from each quadrate were sorted, identified, and counted in the laboratory. The arthropods were identified to the species level and categorized into pest or natural enemies. Rice Insect Pest Species Cnaphalocrocis medinalis (Leaf folder) larvae & adult Sogatella furcifera (Whitebacked planthopper) nymph & adult Nilaparvata lugens (Brown planthopper) nymph & adult Nymphula depunctalis (Caseworm) larvae & adult Nephotettix virescens (Green leafhopper) nymph & adult RESULTS & DISCUSSIONS Trial A Figure 1 & 2 shows that numbers of natural enemies (predators and parasitoids) were increased when the population of pest was high for both seasons. High population of pest will provide food source for the natural enemies. As a result, population of the natural enemies must also increase to balance the ecosystem. Figure 3 demonstrate an interaction pattern between the pest and its natural enemy. For example, population of white back plant hopper was suppressed by predation activity by a spider species called Lycosa sp. This kind of interaction helped to reduce damage to the crop. Natural Enemies Species Harmonia octomaculata (Ladybird beetles) Micraspis discolor (Ladybird beetles) Paederus fuscipes (Rove beetle) Ophionea ishii ishii (Ground beetle) Cyrtorhinus lividipennis (Mirid bug) Limnogonus fossarum (Water striders) Microvelia douglasi (Ripple bugs) Lycosa pseudoannulata (Wolf spider) Oxyopes javanus (Lynx spider) Araneus inustus (Orb weavers) Tetragnatha spp. (Long jawed orb weavers) 1 2 3 4 5 6 7 8 9 35 45 55 65 75 90 DAS Average numbers of pest 0.2 0.4 0.6 0.8 1.2 1.4 1.6 1.8 Average numbers of natural enemies 1 2 3 4 5 6 7 8 9 10 21 40 42 65 85 95 DAS Average numbers of pest 0.2 0.4 0.6 0.8 1.2 1.4 1.6 1.8 Average numbers of natural enemies Table 1 : List of pest & natural enemies species recorded during sampling 1 2 3 4 5 6 7 8 21 30 42 65 85 95 DAS Average number 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Pest Natural enemies Figure 3 : Interaction pattern between insect pest and natural enemies (e.g. WBPH and Lycosa sp.) Figure 1 : Insect sampling at IPM Plot, Bumbong Lima - Off season 2004 Figure 2 : Insect sampling at IPM Plot, Bumbong Lima - Main season 2004/05 Trial B Samplings data from Parit 11, Pasir Panjang showed that there were difference in number of species and individuals of insects recorded between the two different fields (Figure 4). Farmer’s field with pesticide application had a low number of insect pest and natural enemies. This was due to frequent spraying of insecticide done by the farmers. At the same time, the spraying killed the natural enemies in the field. Although IPM plot recorded higher numbers of insect pest, this was balanced by the presence of high number of natural enemies also. High density of natural enemies will suppress the pest population and somehow could reduce the impact of pesticide usage to the natural ecosystem and environment. 1 2 3 4 5 6 7 IPM Farmer 40 DAS 55 DAS 75 DAS 104 DAS DAS A V E R G N U M B L.F. Larvae L1-L3 L.F. Larvae L4-L5 Adult WBPH Nymph WBPH Adult BPH Nymph BPH Adult GLH Nymph GLH Adult Leaffolder Adult Nymphula Lycosa Other spider species Cyrtorhinus sp. Ladybird beetles Paederus Limnogonus CONCLUSION Conservation of these natural enemies and wisely pesticide usage are important in order to have a sustainable rice production. It is encouraged to use pesticide minimally and effectively for pest control and concurrently taking into account the social impact of pesticides on the farming community and the environment. Biological control using natural enemies has been observed to be effective in controlling pest besides having an environmental friendly pest management. Figure 4 : Insect population comparison between farmer’s plot & IPM plot REFERENCES Yasumatsu, K., and C. L., Tan. (1981). Natural enemies of the major insect pests of rice and other agricultural crops in Peninsular Malaysia. World Bank Consultant Report to Malaysian Agricultural Research & development Institute. 49 pp. Yunus, A. (1984). Insect pests of rice in Malaysia. In. Major insect pests of rice plant, John Hopkins Press, Baltimore, pp617-33. ACKNOWLEDGEMENT The authors wish to thank the Director General of Malaysian Agriculture Research and Development Institute (MARDI) for his permission to present this paper. The authors also wish to thank Mr. Hashim Che Mat (MARDI) for his technical assistance. This project was funded by MARDI P&P Project No. 23.