W ith increasing globalization facilitated by World Trade Organization agreements and other treaties, the international trade in agri- cultural commodities has become an integral part of the global economy. The total value of world agricul- tural exports experienced an annual increase of 12.3 percent between 2003 and 2005, from $525 billion to $654 billion. Agricultural commodities are, however, natural carriers of exotic insect pests. These pests can cause major local economic losses when acci- dentally introduced to new areas without co-evolved nat- ural enemies. To reduce the risk of introducing pests, importing countries or regions impose quarantine or phytosani- tary requirements on the hosts of targeted pests. Methyl bromide (MeBr) is the most effective fumigant for pest control, but it is a highly toxic gas and listed as an ozone-depleting chemical along with chloro- fluorocarbons (CFCs) under the Montreal Protocol of 1992. Developed countries were required to freeze production and importation of MeBr in 1994 at the 1991 levels and to reduce the use by 25 percent in 1999, 50 percent in 2001, 70 percent in 2003, and 100 percent in 2005. Developing countries were required to freeze consumption and production of MeBr by 2002, reduce it by 20 percent in 2005, and phase out by 2015. Annual exemptions are granted to companies in the United States and other developed countries to allow continued but limited use of MeBr in postharvest quarantine treatments. But it is expected that MeBr will become more expensive due to reduced production and uncertainty associated with the com- plicated annual approval process for those exemptions. Therefore, there is an urgent need to find environmentally friendly and effective alternatives. RF heating, an alternative to chemical fumigation Researchers have considered using thermal energy to control pests in addition to other environmen- tally friendly methods. A lesson in self- defense can be learned from nature. For instance, sympatric Japanese hon- eybees have evolved a unique ability to kill their natural enemy, the Japanese giant hornet, with thermal energy. When invaded, over 500 bees surround a hornet, vibrate their bodies to 47°C (135°F), and maintain this tem- perature for 20 min. This temper- ature is beyond the lethal temperature for hornets—44°C to 46°C (111°F to 115°F)—but less than that for honeybees— 48°C to 50°C (118°F to 122°F). Thus, when devel- oping effective thermal treatments against insects in commodities, it is critical that we understand the heat toler- ance of the targeted insects and the hosts and develop an appropriate method that delivers thermal energy to complete- ly kill the pests without causing adverse effects to commodi- ty quality. Current developments and achievements Extensive research and development efforts have been made by a multi-disciplinary team of scientists in engineering, entomology, and plant physiology and supported by various programs including the USDA’s IFAFS, NRI, and CSREES, Radio Frequency Energy for Postharvest Control of Pests in Dry Nuts and Legumes Shaojin Wang, Juming Tang, Ralph Cavalieri, Elizabeth Mitcham, and Judy Johnson RESOURCE April/May 2009 17 © Elena Elisseeva/Fotolia.com