عنوان مقاله [English]
Introduction: The suitable weather conditions of Iran makes it as one of the most talented country in producing of the various agricultural products such as grapes and raisins and has a great history in this field. Raisin is a commercial dried fruit, produced by drying of ripe seedless grapes by the moisture content of 16%. A major problem in the production, storage and marketing of stored products is infestation by insect pests. A number of insect species pose a potential threat to a variety of stored products. The Oryzaephilus surinamensis L. and Ephestia kuehniella Zeller. Have a widespread distribution in the most part of the world. These species are recognized as the cosmopolitan pests attacking stored-products and cause serious losses both in quantity through feeding damage and quality by contaminating the product with its cast skin and frass. Considering economic importance of pests and problems arising from the use of chemical insecticides and fumigants, it is necessary to replace them with the other appropriate methods. The traditional methods of pest control, while having many advantages such as ease of operation and low cost, have some disadvantages such as slow operations, creation of environmental pollution residues, negative impact on product quality and health hazards on the operator. The use of alternative methods seems to be necessary because of concerns about the health hazards of chemical pesticides and its environment pollution. The researches has been conducted on the ionizing radiation, controlled atmosphere, cold treatment, conventional hot air or water heating and novel radio frequency and microwave dielectric heating for controlling the insects. The microwave heating is based on the transformation of alternating electromagnetic ﬁeld energy into thermal energy by affecting the polar molecules of a material. The most important characteristic of the microwave heating method is volumetric heating. Dielectric heating which covers both radio frequency and microwave has been investigated for insect control in foods. Microwaves radiation are a part of electromagnetic spectrum with wavelengths less than radio waves and more than infrared waves, which their frequency range are 300MHz to 30GHz.
Materials and Methods: Two insect species, the lesser grain borer, O. surinamensis L. and mediterranean flour moth, E. kuehniella Zeller. Were reared under the laboratory condition at temperature of 27±2 C and relative humidity of 65%±5. The lesser grain borer was reared on the medium contains 99% wheat ﬂour mixed along with 1% brewer’s yeast and the mediterranean flour moth were reared the medium contains on 90% wheat ﬂour mixed along with 10% brewer’s yeast. In this study, the microwave oven (Media -MW-F-282ELKS) was used which operates at 2450 MHz and variable power levels. The samples were exposed to microwave treatments at three power levels (450, 270 and 900W) for four exposure times (20, 30, 40 and 50s). Each treatment (power and exposure time combination) was replicated three times.
Results and Discussion: The mortality of E. kuehniella at the highest level of microwave power (900W) and for 20, 30, 40 and 50s exposure times were 51.67%, 71.63%, 91.53% and 100%, respectively. For the microwave power of 900W and exposure time of 20, 30, 40 and 50 s the mortality of O. surinamensis was 68.03%, 88.23%, 91.67% and 100%, %, respectively. The results showed, at a power level of 450W and an exposure time of 20s, the mortality of E. kuehniella and O. surinamensis were 20% and 33.33%, respectively. As the power increases to 720 and 900W, the mortality of E. kuehniella and O. surinamensis enhances to 33.33% and 56.63%, respectively. With increasing the exposure time, higher mortality was achieved at lower power levels. For the microwave power of 720W and exposure time of 40s, the mortality of E. kuehniella was 61.53%. When the exposure time was increased to 50s, the mortality of E. kuehniella was achieved 86.63% for the power of 720W. Also for the microwave power of 450W and the exposure time of 50s, the mortality of O. surinamensis was obtained 78.33%. When the microwave power was increased to 900W, the mortality of 100% was obtained.
Conclusion: The results showed the complete mortality for the insects, E. kuehniella and O. surinamensis, were at 900 W and exposure time of 50s. The lowest rate of mortality for both of them was observed at 450 W and exposure time of 20 s. The increase of microwave power and exposure time or both together lead to increase of mortality. It can be concluded that the mortality was affected by microwave power and exposure time.