Outside view of a rice flake plant

Rice Flake Plant

Facility Type: Rice Flake Plant

Location: Missouri, USA

Objective: Controlling Stored Product Insects (SPIs), by elevating and then holding the temperatures within the Plant between 122-140°F/50-60°C for 24 hours. Indirect efficacy of heat treatment on resident insect populations before and after heat treatment.

Equipment Used: Direct-fired, make-up air gas heaters using Propane as fuel, industrial strength fans for airflow management, high temperature fabric ductwork and real-time wireless temperature monitoring system to monitor and manipulate temperatures for effective disinfestation.

Heater models used: (1) THP-4500 (4.5 Million BTUs/hr)

Process: Tempering room, one of the areas of Rice Flake processing plant, was heat treated using one propane-fueled, direct fired heater with an output of 4.5 MBTUs/hr. Positive pressurization principle was applied wherein fresh outside air is heated and blown (through a high velocity blower) into the space to be heated using an array/layout of high temperature fabric ductwork for proper distribution of hot air. High temperature duct coupled with multiple fans strategically placed throughout the heated space ensured uniform lethal temperature (122-140°F), thus eliminating hot or cold spots. Hot or cold spots within the heated space can be either detrimental to the equipment or result in insect survival, respectively. Forced air leading to positive pressurization of heated space totally eliminates the need to seal the heated space unlike chemical fumigation.

Time to reach minimum 122°F/50°C in the Tempering room was less than 1.5 hours due to smaller volume and lower thermal mass. This was followed by holding the temperatures (122-140°F) for 24 hours to emulate chemical fumigation. Temperatures were monitored using HOBO® data loggers in various locations within the facility in addition to real-time wireless temperature sensors. The effectiveness of the heat treatment was evaluated with insect bioassays placed adjacent to the data loggers in order to correlate temperature and insect mortality rates. The insect bioassays were prepared and mortality tests were performed in the Stored Products Insects Research and Education Laboratory at Kansas State University, Manhattan, KS.

The indirect efficacy of structural heat treatments was assessed by monitoring the resident insect populations before and after the heat treatment by monitoring insects in the facility using commercial food-baited traps. The traps, trap monitoring, and results were provided by Scientists from the USDA, Agricultural Research Service, Center for Grain and Animal Health Research, Manhattan, KS.

Summary of Outcome:

Insect Bio-assays results: One hundred percent of egg mortality at all locations was observed after 3 and 6 hours into the heat treatment where mean temperatures attained were 50.0 and 55.4°C, respectively. However, adults had a lower mortality compared to eggs for all the pick-up times except for the last pick-up time at 24 hours, where it was 100% for both life stages.

Indirect Efficacy of Heat: In the monitoring periods prior to the heat treatment, cigarette beetle captures were primarily in the warehouse and the tempering room. The traps in the warehouse with high captures of cigarette beetle tended to around the adjacent walls of the tempering room and the warehouse. Captures of cigarette beetle outside and in the processing area were very low. This pattern of capture is consistent with tempering room being the source of cigarette beetles. Warehouse beetle was also captured at the facility, but primarily outside and some inside the warehouse building – trap located near outside trash bins had the highest captures. Pattern for warehouse beetles was that it was primarily of outside origin with occasionally some immigration into the warehouse. Some Indianmeal moths were captured outside, but none inside the facility.

Following the heat treatment, there was a 91% reduction in cigarette beetle captures in the tempering room immediately following the heat treatment. There were also corresponding decreases in the processing room and warehouse as well which were not treated which is consistent with the tempering room serving as the source for the populations.

Acknowledgements: We thank the commercial facility for cooperating on this research project that was supported by funds from EPA-Region VII and by the Propane Research and Education Council, Washington, D. C. We are grateful to Grain Science & Industry Department, Kansas State University & USDA, Agricultural Research Service, Center for Grain and Animal Health Research, Manhattan, KS for scientific evaluation insect-bioassays and assessment of indirect efficacy of heat, respectively.

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