Effect of different sanitation levels on survival of Tribolium castaneum (Coleoptera: Tenebrionidae) exposed to high temperatures during heat treatment of a flour mill

Unsanitary conditions in flour mills are potential harborage sites for the red flour beetle, Tribolium castaneum (Herbst), a major pest in mills. The effect of different levels of flour dust on survival of T. castaneum life stages during a practical heat treatment of a pilot scale flour mill was investigated. Two separate experiments were conducted during 13-15 May 2009 and 25-26 August 2009 heat treatments of Kansas State University’s Hal Ross Flour Mill. In the first experiment, the effect of high temperatures (50-60^oC), and two levels of sanitation (dusting and 2 cm deep flour), on eggs, young larvae, old larvae, pupae and adults confined in plastic boxes was evaluated. In the second experiment, 0.1, 0.2, 1, 3, 6, and 10 cm flour depths were simulated using 20 cm diameter and 15 cm high PVC rings to evaluate survival of T. castaneum eggs or adults during the two heat treatments. Temperatures in box and PVC ring bioassays at all sanitation levels were recorded. Temperature profiles within the mill during the 24 h heat treatment were also recorded. In box bioassays, essentially none of the life stages survived the 24 h heat treatment except in a few locations. In PVC ring bioassays, both the egg and adult mortality at all flour depths was 100% only on the third floor of the mill after 24 h and not on the first floor. The survival of insects is related to how fast temperatures reached 50^oC and how long temperatures were held above 50^oC.