Assessment of a mobile solar biomass hybrid dryer for insect disinfestation in dried maize grains: Presentation

Considerable losses of stored food grains occur through insect infestation in tropical countries because climatic conditions are conducive for insect activity throughout the year. Studies have shown that in order to kill stored grain insects of all life stages temperatures above 50°C are required. However, grain simply laid in the sun or placed in a solar dryer does not reach such high temperatures. This study describes the use of a 1 tonne batch capacity mobile solar biomass hybrid dryer for disinfestation of infested maize and prevention of F1 progeny emergence in stored maize grains. To assess the effect of temperature and exposure period on mortality of maize weevils, infested maize in experimental cages were exposed for 3 and 6 hours of thermal disinfestation treatment in the dryer. Comparing the heat generated in the dryer under hybrid mode operation where additional heat is generated by a biomass furnace in addition to solar, a mean temperature of 67°C was recorded compared to a mean ambient temperature of 36°C. Results showed that there was no significant difference (p < 0.05) in mortality of maize weevils during disinfestation treatment for 3 and 6-hour exposure periods. Mortality of 100% was obtained for samples disinfested in the highest tray (level 4) in the dryer. After 30 days of storage of disinfested maize grains, there was no emergence of F1 progeny from the maize grains exposed for 3 and 6 hours. Effect of ambient temperature and open sun exposure periods in the control set-up resulted in low mean percent mortality. Also, samples from the control set-up at both 3 and 6-hour exposure periods showed emergence of F1 progeny after storage. From this study, it can be concluded that an exposure period of 3 hours (or perhaps even less) in the solar biomass hybrid dryer could prevent damage by Sitophilus zeamais to stored maize grains after thermal disinfestation at a mean temperature of 67°C.Considerable losses of stored food grains occur through insect infestation in tropical countries because climatic conditions are conducive for insect activity throughout the year. Studies have shown that in order to kill stored grain insects of all life stages temperatures above 50°C are required. However, grain simply laid in the sun or placed in a solar dryer does not reach such high temperatures. This study describes the use of a 1 tonne batch capacity mobile solar biomass hybrid dryer for disinfestation of infested maize and prevention of F1 progeny emergence in stored maize grains. To assess the effect of temperature and exposure period on mortality of maize weevils, infested maize in experimental cages were exposed for 3 and 6 hours of thermal disinfestation treatment in the dryer. Comparing the heat generated in the dryer under hybrid mode operation where additional heat is generated by a biomass furnace in addition to solar, a mean temperature of 67°C was recorded compared to a mean ambient temperature of 36°C. Results showed that there was no significant difference (p < 0.05) in mortality of maize weevils during disinfestation treatment for 3 and 6-hour exposure periods. Mortality of 100% was obtained for samples disinfested in the highest tray (level 4) in the dryer. After 30 days of storage of disinfested maize grains, there was no emergence of F1 progeny from the maize grains exposed for 3 and 6 hours. Effect of ambient temperature and open sun exposure periods in the control set-up resulted in low mean percent mortality. Also, samples from the control set-up at both 3 and 6-hour exposure periods showed emergence of F1 progeny after storage. From this study, it can be concluded that an exposure period of 3 hours (or perhaps even less) in the solar biomass hybrid dryer could prevent damage by Sitophilus zeamais to stored maize grains after thermal disinfestation at a mean temperature of 67°C