In agriculture, after the product is harvested, it has been stored before export. For a long time that the products are stored, so the pest which is the rice weevils devours and destroys the products. Hence, the dielectric heating is an important technique to control insects in the grain after harvesting. The advantage of the radio frequency (RF) is unadulterated toxin. Consideration to an effect of the dielectric heating, electric field distribution and intensity analysis are occurred at the dielectric load. When the materials for heat are grains and insects, this research studies and analyses the dielectric heating by using the electric field intensity that is occurred with the grains and insects. The rice and the rice weevils are used for dielectric materials in this analysis. In addition, the effects in each material are compared and to control overheat of the grains. The heat is occurred by using rectangular plates to generate the electric field. The plates are made from a copper material with size of 5 x 20 cm, thickness of 0.5 mm. An analysis is classified into two cases as case I uses the rice weevil placed1 set and various positions on plate and case II placed the rice weevil 2 set and two different positions on the plates. The feed points of rectangular plate are optimized by using CST EM studio program with 1000 watt electrical power at 39 MHz resonance frequency, which is a responsible frequency of rice weevil [10], [11]. The most electric field intensity is occurred when the location of materials are located near the feed point. At the same position, the rice weevils have effect of electric field intensity more than rice because the frequency respond is appropriated to the rice weevils. It can be applied for the dielectric heating applications to eliminate insects.