Submitted to: Journal of Economic Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/27/2012
Publication Date: 2/1/2012
Citation: Brijwani, M., Subramanyam, B., Flinn, P.W., Langemeier, M.R., Hartzer, M. 2012. Susceptibility of Tribolium castaneum life stages exposed to elevated temperatures during heat treatments of a pilot flour mill: influence of sanitation, temperatures attained among mills floors, and costs. Journal of Economic Entomology. 105(2): 709-717. http://dx.doi.org/10.1603/EC11114. Interpretive Summary: The red flour beetle is one of the most common and serious insect pests of flour mills. The phase out of the fumigant methyl bromide in the United States in 2005 because of its adverse effects on stratospheric ozone has generated renewed interest in heat treatments to disinfest flour mills. It is well known that grain and grain products are poor conductors of heat, based on temperatures measured during facility heat treatments. However, data are lacking on the influence of sanitation, such as removal of flour residues, on response of stored-product insects to heat treatments. In collaboration with scientists at Kansas State University, experiments were conducted to investigate the influence of sanitation on mortality of different stages of the red flour beetle exposed to 24-hour heat treatments using forced-air gas heaters. Two sanitation levels, a dusting of wheat flour and 2-cm deep flour, were created in 25 plastic bioassay boxes, each holding eggs, young larvae, old larvae, pupae, and adult red flour beetles. The maximum temperature in the bioassay boxes and in the mill was lower on the first floor than on other floors. Mortality on the first floor ranged from 56 to 99%, and 93 to 100% on the other floors. Adults were the least susceptible stage. Mortality in bioassay boxes with 2-cm deep flour was generally lower than those with a dusting of flour. The cost of the heat treatments in the study ranged from $75.30 to $111.87 per 1,000 cubic feet. These results show that an effective heat treatment can be conducted within 24 h, provided the mill is cleaned to remove flour residues and temperatures reach 50°C and are held above 50°C for at least 12 hours.
Technical Abstract: The influence of sanitation on responses of life stages of the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), was investigated in a pilot flour mill subjected to three, 24 hour heat treatments using forced-air gas heaters. Two sanitation levels, dusting of wheat flour and 2-cm deep flour, were created in 25 plastic bioassay boxes, each holding eggs, young larvae, old larvae, pupae, and adults of T. castaneum plus two temperature sensors. Data loggers (48) were placed on the five mill floors to record air temperatures. The time required to reach 50ºC, time above 50ºC, and the maximum temperature among mill floors and in bioassay boxes were examined. The maximum temperature in bioassay boxes and in the mill was lower on the first floor than on other floors. This trend was apparent in time required to reach 50ºC and time above 50ºC, especially in compartments with 2-cm deep flour. The mean ± SE mortality of T. castaneum life stages on the first floor was 55.5 ± 12.9 to 98.6 ± 0.8 and 93.2 ± 6.7 to 100 ± 0.0 on other floors, and adults were the least susceptible stage. Mortality of T. castaneum stages in compartments with 2-cm deep flour was generally lower than those with flour dust. The heat treatments costs ranged from $25,605 to $38,005. An effective heat treatment can be conducted within 24 h, provided the mill is sanitary and temperatures reach 50°C and are held above 50°C for several hours.