Solar Thermal Control of Insects in Stored Wheat Grain

Abstract

The presence of insect pests in stored grains constitutes an undesirable condition leading to product losses, lesser quality, and reduced market value .For prevention of damage and losses by insects’ infestation; all insects present in the stored product must be eliminated at any stage of their life. The method used for insect pest control, such as chemical methods; lead to several problems and hazards for consumers. Heat treatment seems to be a good solution, but it is costly and requires special facilities for application. Therefore, the aim of this study was to use solar energy, as source of heat, for thermal energy control of store insects, in an attempt to find a safer, effective and cheap control measure. To study the effect of cover, unpainted metal, black paint and black painted with cover, three containers were made from metal, one unpainted and one painted with black paint and the third painted with black paint and covered with polythene. All containers were filled with equal amounts of wheat grains and kept out door for exposure to direct sun radiation. Temperature measurements were taken at two hours interval from 8:00a.m.to 1:00p.m for the first period and from1:00 p.m. to 5:00 p.m. for the second period. Three structures of different geometrical shapes made of metal were used. The geometrical shapes of these structures were pyramid, cylinder and cube. Three containers were made from each structure, two from each group (out of three) were painted black and one was not painted. One of the two painted containers was covered with transparent polythene. All containers were filled with wheat grains, and temperature measurements were taken at two hours interval from 8:00a.m.to 4:00p.m. The highest temperature was recorded in black painted container with cover (49.8℃),followed by the black painted (47.9) ℃ then the unpainted container (46.5℃ ).These temperature were found to be greater than the lethal temperature (45℃ ) for all developing stages of store insects. The structures with inclined surface, like pyramid group, recorded highest temperatures compared to vertical structures (cylindrical and cubic shapes). Treatment of wheat grains at temperatures of 55 ℃ and 70℃ for 2 hours to 24 hours did not indicate any harmful effect in all studied parameters (moisture content, protein, fat content, ash, germination and one thousand kernels weight). Generally, it could be concluded that solar energy could be used for control of store insects with simple treatment of the containers tested in this study under Sudan conditions.