Journal of Forestry Research, 17(1): 44–46 (2006) 44 Infestation of insect pests in tree-rice agroforestry system K. K. Islam 1 , G. M. M. Rahman 1 and A. T. M. Rafiqul Hoque 2* 1. Department of Agroforestry, Bangladesh Agricultural University, Mymensingh, Bangladesh 2. Institute of Forestry and Environmental Sciences, Chittagong University, Chittagong 4331, Bangladesh Abstract The prevalence of insect pests was studied on rice BR11 (mukta) as understory crop grown in association with 11 years old selected tree species viz, Akashmoni, Jhau and Albida in the field laboratory of the Department of Agroforestry, Bangladesh Agricultural University (BAU), Mymensingh during the period from July to December, 2003. Among the three species Albida and Jhau possessed the largest canopy and there light penetration rate were high. On the other hand, Akashmoni had the lowest canopy but it penetrated low amount of light. Albida-rice association showed the lowest infestation of major rice insects followed by Jhau-rice association, while Akashmoni-rice association showed the highest insect infestation. Light intensity in the control plot (absent of tree species) was maximum and it caused minimum severity of insects infestation as compared to other associations. From the result it appeared that light interception has the relationship with insect population in rice. Therefore, tree species having sparse canopy which allowed easy penetration of sunlight is suitable for tree-rice agroforestry system. Keywords: Light interception, Insect infestation; Rice, Agroforestry. CLC number：S435.112.1 Document code: A Article ID: 1007-662X(2006)01-0044-03 Introduction Agroforestry is a production technique or method that com- bines agriculture and forestry on same piece of land to fully util- ize the natural resources of sunlight, water and nutrition. Crop- land agroforestry is one of the most important and widely used practices where trees are grown in and around the crop field. Cropland agroforestry is not a traditional practice except in a few places of north-western part of Bangladesh, where tree species like Date palm, Babla, Khoir, and Palmyra palm grow naturally on agricultural lands in the higher parts of the Ganges flood plain and are intentionally retained and maintained by the farmers for different house hold utilities and products and also for earning money (Abedin and Quddus 1991). Cropland agroforestry includes trees that are cultivated along with various annual crops like paddy, wheat and other cash crops in farmers land. In this country farming is mostly subsistence and crop based. Rice is the principal crop covering about 80% of the total cropped land of the country Trees are simultaneously planted in rows, sparsely in crop field and/or along the ails (boundary lines). The continuous rice cropping has created fa- vorable condition for certain kinds of insect pests. Moreover, the prevailing warm and humid conditions have favored rapid multi- plication of insect pests and diseases. The estimated annual loss of rice in Bangladesh due to insect pest and diseases amounts about 1.5 to 2.0 million tons (Siddique 1992). So far 175 species of insects have been recorded as rice pests (BRRI 1985). Of these 20-30 species are economically important. The rice hispa, stem borers, plant hoppers and rice ear cutting caterpillar cause serious damage to rice crop each year. Major insect pests cause about 13% yield losses to Boro, 24% to Aus and 18% to Aman crops (Miah and Karim 1984). Biography: A. T. M. Rafiqul Hoque (1972): * Corresponding author, Male, Assistant Professor in the Institute of Forestry and Environmental Sciences, University of Chittagong, Chittagong-4331, Bangladesh e-mail: rafiqcu@yahoo.com Received date: 2005-09-10; Accepted date: 2005-11-10 Responsible editor: Chai Ruihai As the practices of simultaneous cultivation of rice along with inter-cropping of suitable tree species is gaining popularity, the prevalence of major insects is necessary to determine. Keeping this view in mind, the present research has been undertaken to determine the prevalence of major insect pests of rice grown in association with three selected tree species. Materials and methods The experiment was conducted at the Field Laboratory, De- partment of Agroforestry, Bangladesh Agricultural University, Mymensingh during July–December 2003. The experiment was carried out in RCBD with three replications using the recom- mended rate of fertilizers for rice. The treatment combinations were T o = Without tree × Rice association; T 1 = Akashmoni × Rice association; T 2 = Jhau × Rice association and T 3 = Albida × Rice association. Acacia auriculiformis (Akashmoni), Casuarina equisetifolia (Jhau) and Acacia albida (Albida) all the tree spe- cies were 11 years old and rice was used as understory crop. The crown diameter of each of the 3 trees measured along North-South and East-West axis using a measuring tape. Four rice plots each of 0.75m×1.0m were laid around a tree. Forty days old seedlings of BR-11 were collected and two/three seed- lings per hill were planted in all the plots including control. To estimate the insect infestation the sampling was done by means of a square sampler (0.5 m x 0.5m) made up of jute sticks. Dur- ing sampling the sampler was placed on the emerged rice plants inside the field. The number of infested tillers, leaves and spikelets were counted, following the method outlined by Dyck and Hsieh (1972). The infestation percentage was calculated using the formula = A/B × 100, where, A=Number of infested tillers or spikelets or leaves and B= Number of total tillers or spikelets or leaves. The estimation of insect infested tillers, leaves and spikelets in the rice fields was carried out at different stages then average mean of four stages was taken. Light inten- sity in each of the tree-rice associations was measured with the help of “Quantum Sensor”. Light was measured above the can- opy of each tree-rice association by different orientation as per design and treatment. Three readings were taken from each ori