Submitted to: Journal of Stored Products Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/18/2014
Publication Date: 4/13/2014
Citation: Yan, R., Huang, Z., Zhu, H., Johnson, J.A., Wang, S. 2014. Thermal death kinetics of adult Sitophilus oryzae and the effects of heating rate on thermotolerance. Journal of Stored Products Research. DOI: 10.1016/j.jspr.2014.03.006. Interpretive Summary: The rice weevil is one of the most destructive and widespread postharvest pests in stored grains and legumes. Environmental restrictions on the use of methyl bromide fumigation and the occurrence of insect resistance to phosphine have generated interest in alternative non-chemical methods. Microwave and radio frequency energy can be used to rapidly heat product, killing any infesting insects. To develop treatment protocols for controlling rice weevil with radio frequency energy, basic data on insect heat tolerance is needed. A heat block system was used to develop mathematical models for how adult rice weevils respond to temperatures from 44 to 50 degrees C at a heating rate of 5 degrees C/min. The effect of heating rates on mortality was also examined. The exposures needed to completely kill adult rice weevils ranged from 130 minutes at 44 degrees C to 4 minutes at 50 degrees C. The activation energy for killing adult rice weevil was calculated to be 505 kJ/mol, suggesting that rice weevil adults are more sensitive to temperature change than previously studied moth species. Adult rice weevils at low heating rates common to conventional heating methods were significantly harder to kill than those at the high heating rates found in microwave and radio frequency heating. The enhanced thermal tolerance observed at low heating rates may be caused by heat acclimation of test insects during lengthy exposures to non-lethal temperatures. Our results suggest that the rapid temperature rise characteristic of heating with microwave or radio frequency would avoid acclimation and be a distinct advantage for the use of this technology.
Technical Abstract: Information on thermal death kinetics of targeted stored insects under different heating conditions is essential for developing postharvest disinfestation treatment protocols. Using a heating block system, the thermal death kinetics of adult rice weevil were determined at temperatures from 44 to 50°C at 2°C intervals at a heating rate of 5°C/min. The effects of heating rates (0.1, 0.5, 1, 5 and 10°C/min) on mortality were also examined. The results showed that thermal death curves of the rice weevil followed a 0-order kinetic reaction model. The required holding times for achieving 100% mortality were 130, 50, 12, and 4 min at 44, 46, 48, and 50°C, respectively. The activation energy for killing rice weevil was 505 kJ/mol and the z value obtained from the thermal death time curve was 3.9°C. Insect mortality after a 20 min exposure to 46°C at low heating rates (0.1 or 0.5°C /min) was significantly lower than that at high heating rates (1 to 10°C/min). The information provided by thermal death kinetics for rice weevils is useful in developing effective postharvest thermal treatment protocols.