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Title: Efficacy of heat treatment for disinfestation of concrete grain silos

item OPIT, G - Oklahoma State University
item Arthur, Franklin
item BONJOUR, E - Oklahoma State University
item JONES, C - Oklahoma State University
item PHILLIPS, T - Kansas State University

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2011
Publication Date: 8/11/2011
Citation: Opit, G.P., Arthur, F.H., Bonjour, E.L., Jones, C.L., Phillips, T.W. 2011. Efficacy of heat treatment for disinfestation of concrete grain silos. Journal of Economic Entomology. 104(4):1415-1422.

Interpretive Summary: Heat treatments are being used to disinfest flour mills but there is no information on the utility of this technique to disinfest empty grain silos. We conducted field trials by placing live lesser grain borers, red flour beetles, or two psocid species inside containers with wheat and/or flour media and suspending those containers at different heights inside empty silos. Propane heat was generated from commercial equipment and introduced into the bottom of the silos. When temperatures exceeded 122°F for at least 6 hours, complete mortality of all insects and life stages generally occurred. The wheat inside the containers did provide some insulating effect from the heat. The lesser grain borer was more heat-tolerant than the red flour beetle, and one of the psocid species was more tolerant than the other. Most of the insect survival occurred in the containers that were in the top or mid-points of the silos. Results show heat could be used to disinfest empty silos, but cleaning and sanitation prior to heat treatment might be necessary to maximize effectiveness.

Technical Abstract: Field experiments were conducted in 2007 and 2008 to evaluate heat treatment for disinfestations of empty concrete elevator silos. A Mobile Heat Treatment Unit was used to introduce heat into silos to attain target conditions of 50°C for at least 6 h. Ventilated plastic containers with a capacity of 100 g of wheat held Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). Polyvinyl chloride containers with a capacity of 300 g of wheat held adults of Liposcelis corrodens (Heymons) (Psocoptera: Liposcelididae) and Liposcelis decolor (Pearman) which were contained in 35-mm Petri dishes within the grain. Containers were fastened to a rope suspended from the top of the silo at depths of just under the top manhole, 10 and 20 m below the top, and at the bottom (30 m from the top). When the highest temperature achieved was >50°C for 6 hours, parental mortality of R. dominica and T. castaneum, and both psocid species was generally 100%. Progeny production of R. dominica occurred when there was parental survival, but in general R. dominica appeared to be more heat-tolerant than T. castaneum. There was 100% mortality of L. corrodens at all depths in the heat treatments but only 92.5% mortality for L. decolor, with most survivors located in the bioassay containers at the top of the silo. Results show wheat kernels may have an insulating effect and heat treatment might be more effective when used in conjunction with sanitation and cleaning procedures.