ARS | Publication request: Impact of varying levels of sanitation on mortality of Tribolium castaneum eggs and adults during heat treatment of a pilot flour mill

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 23, 2012
Publication Date: February 1, 2012
Citation: Brijwani, M., Subramanyam, B., Flinn, P.W. 2012. Impact of varying levels of sanitation on mortality of Tribolium castaneum eggs and adults during heat treatment of a pilot flour mill. Journal of Economic Entomology. 105(2): 703-708. http://dx.doi.org/10.1603/EC11115.

Interpretive Summary: The red flour beetle is the most common and economically damaging insect pest in 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 using heat treatments for insect control in flour mills. Based on temperatures measured during facility heat treatments, it has been shown that flour is a poor conductor of heat and data are lacking on the mortality of insects in flour residues during heat treatments. In collaboration with scientists at Kansas State University, experiments were conducted to investigate the influence of residual flour depth on mortality of red flour beetle eggs and adults during two separate 24-hour heat treatments of a flour mill. Red flour beetle eggs or adults were placed inside plastic rings containing various amounts of wheat flour ranging from 0.4 to 6 inches to simulate different residual flour levels that may exist in a flour mill. The protective effects of flour residue on insect mortality during the heat treatment were much greater for adults than for eggs. Flour depths of 1 inch or greater had less than 10% adult mortality, whereas the egg stage had 70% mortality at 1 and 2 inches and 40% mortality at 4 inches. This study showed that flour residues in mills can reduce the effectiveness of heat treatments.

Technical Abstract: The influence of sanitation on responses of life stages of the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), an economically important pest in flour mills, was investigated in a pilot flour mill subjected to two, 24-h heat treatments. One hundred eggs or 100 adults of T. castaneum were exposed inside each 20-cm diameter by 15-cm high PVC ring holding 0.1-, 0.2-, 1.0-, 3.0-, 6.0-, or 10.0-cm deep wheat flour to simulate different sanitation levels that may exist in a flour mill. These rings were placed on the first and third floors of a pilot flour mill. On the first floor, temperatures inside rings with eggs reached 50°C in 7 to 11 h only in 0.1- and 0.2-cm deep flour treatments. In all other treatments the maximum temperatures attained were generally below 50°C and inversely related to flour depth. Adults of T. castaneum on this floor were less susceptible than eggs. The egg mortality decreased linearly with an increase in flour depth whereas that of adults decreased exponentially. All eggs and adults in rings on the third floor were killed irrespective of flour depth because temperatures inside rings reached 50°C in 15 to 17 h and were held above 50°C for 6 to 8 h with the maximum temperatures ranging between 55.0 and 57.0°C. Although the protective effects of flour on survival of T. castaneum eggs and adults were evident only if temperatures did not reach 50ºC, removal of flour accumulations is essential to improve heat treatment effectiveness.