Facility Type: Sunflower Seed Processing Plant
Location: Missouri, USA
Objective: Controlling Stored Product Insects (SPIs), mainly red flour beetles, 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, MBTUs/hr), (1) THP-1400 (1.4.MBTUs/hr.), (1) THP-550 (0.55 MBTUs/hr),
Process: Two areas of a commercial sunflower seed processing facility namely the dry roast room (DRR) and bulk building unloading/storage room (BBU) were heat treated to lethal temperatures (122-140°F) to manage SPIs. The heat treatment was performed with direct fired heaters using Propane as source of fuel. The process uses the principle of positive pressurization of space to be heated. Fresh ambient outside air entering the heater is heated and forced into heated space by a high velocity blower. An array of high temperature ductwork coupled with multiple fans is laid out in heated space to attain and maintain temperature range (122-140°F) lethal to SPIs. 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 both DRR and BBU rooms ranged from 3 to 4 hours 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: After 27.7 hours with a mean temperature of 57.8°C ± 0.7 (136.04°F), the mean mortality rate of both young larvae and adults of the red flour beetle in the dry roast room (DRR) was 100%. After 27.7 hours with a mean temperature of 57.8°C (114.44°F), the mean mortality rate of young larvae of the red flour beetle in the bulk storage room (BBU) was 99.6% ± 0.4% and the mean mortality rate of adults of the red flour beetle in the bulk storage room was 98.8% ± 2.5%.
Indirect Efficacy of Heat: Prior to the heat treatments the captures of Indianmeal moth were declining due to seasonal patterns, resulting in low insect activity during heat treatment. The Indianmeal moth activity was found during the monitoring period immediately after the heat treatment, however, in the following two periods there were no captures. Due to the seasonal patterns in insect activity and temperature it is difficult to draw firm conclusions about the impact of the heat treatment on the resident insect populations, but results from bioassays provide direct assessment of effectiveness of the heat treatment. Heat treatment, like fumigants, does not have residual effectiveness. However, depending on the source of insect populations and delays in population rebounds, a period free of insect captures or low captures following a heat treatment was expected. However, the fact that companies keep their doors open allows insects from outside to enter facilities. Additionally, the onset of cooler temperatures in October and November may have resulted in low insect captures observed after the heat treatment.
Acknowledgements: Thanks are due to 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 the Grain Science & Industry Department, Kansas State University & USDA, Agricultural Research Service, Center for Grain and Animal Health Research, Manhattan, KS for scientific evaluation of insect-bioassays and assessment of indirect efficacy of heat, respectively.