Efficacy of atmospheric and pressurized carbon dioxide or air against Sitophilus zeamais Motchulsky (Coleoptera: Curculionidae) and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) in milled rice Athapol Noomhorm a , Porntip Sirisoontaralak b, * , Jaitip Uraichuen c , Imran Ahmad a a Food Engineering and Bioprocess Technology Program, Asian Institute of Technology, P.O. Box 4, Pathumthani, Thailand b Division of Food Science and Nutrition, Faculty of Agricultural Product Innovation and Technology, Srinakharinwirot University, Wattana, Bangkok, Thailand c Post-harvest and Products Processing Research and Development Office, Department of Agriculture, Chatuchak, Bangkok, Thailand article info Article history: Accepted 7 May 2013 Keywords: Sitophilus zeamais Tribolium castaneum Milled rice Carbon dioxide High pressure abstract Carbon dioxide gas was evaluated in the laboratory for control of Sitophilus zeamais Motchulsky and Tribolium castaneum (Herbst) in milled rice using a specially designed pressure chamber. Tests were conducted at atmospheric pressure with 60, 80 and 100% carbon dioxide and with 100% carbon dioxide pressurized to 4, 6 and 8 bars. LT 99 were 79, 78, and 148 h for all life stages of S. zeamais exposed to 60, 80 and 100% carbon dioxide, whereas, they were 59, 51 and 66 h for T. castaneum. Pure carbon dioxide controlled the adult stage, but there tended to be no significant differences of carbon dioxide concentrations on mortality of immature stages. When pure carbon dioxide was pressurized, mortalities of the two insect species were increased significantly. LT 99 values decreased with levels of applied pressure: 29, 9.0 and 4.8 h for S. zeamais and 15, 5.8 and 2.3 h for T. castaneum at pressures of 4, 6 and 8 bars, respectively. Sitophilus zeamais was more tolerant than T. castaneum to carbon dioxide gas. The adult was the most susceptible stage, however, immature stages responded differently to carbon dioxide gas applied at varying concentrations and pressure levels. Adult mortalities were lower when air was used in the pressure chamber instead of carbon dioxide. Pressurized carbon dioxide at relatively low pressure (4e8 bars) was found effective in controlling all live stages of S. zeamais and T. castaneum in milled rice with shorter exposure times than at atmospheric pressure using an inexpensive set of equipment as compared to high pressure carbon dioxide fumigation (20e30 bars). Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction One of the most important problems faced during storage of milled rice is insect infestation. The major species of stored product insects found in rice mills in Thailand are the Maize Weevil, Sito- philus zeamais Motchulsky, and the Red Flour Beetle, Tribolium castaneum (Herbst). Hidden infestations of insect eggs inside and outside rice kernels cause significant quality loss when insects hatch from eggs develop in the sealed plastic packages. As a common practice, rice is treated with chemical fumigants to prevent insect development. However, with increasing consumer demands for chemical-free food products, there have been a number of attempts to introduce other insect control methods to replace fumigation. Carbon dioxide could be an alternative to chemical fumigants as it is safe to the environment but can kill insects. Most stored product insects are killed under atmospheres of <3% O 2 or >40% CO 2 (Bailey, 1965). To obtain a complete kill of all growth stages, carbon dioxide fumigation requires lengthy exposure periods. Annis (1987) reported that Sitophilus oryzae L. (rice weevil) was amongst the most tolerant stored product insects to carbon dioxide rich atmospheres. The proposed exposure time to control S. oryzae when using >40% carbon dioxide at 25  C was 15 days, which was assumed to be adequate for all other species. However, to obtain high acute mortality for this kind of insect, high concentrations of carbon dioxide are needed but with nil oxygen effectiveness is reduced. Lindgren and Vincent (1970) found that atmospheres with 40e90% of carbon dioxide in air were more toxic to S. oryzae adults * Corresponding author. Tel./fax: þ66 2 649 5000x8304. E-mail address: porntips@swu.ac.th (P. Sirisoontaralak). Contents lists available at SciVerse ScienceDirect Journal of Stored Products Research journal homepage: www.elsevier.com/locate/jspr 0022-474X/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jspr.2013.05.002 Journal of Stored Products Research 54 (2013) 48e53