A Population-Dynamics Approach to Assess the Threat of Plant Pathogens as Biological Weapons against Annual Crops

Abstract

I recent years there has been considerable concern expressed in the scientific and popular literature about the threat of biological terrorism (Simon 1997, Henderson 1998, Abelson 1999,Atlas 1999, Osterholm 1999, Stone 2000, Hardy 2001, Stimson Center 2001). This general interest had been propelled by US executive orders on weapons of mass destruction, White House initiatives on biological and chemical weapons preparedness (White House 1994, 1998a, 1998b, 1998c, 1999a), and the release of information from the former Soviet Union on the extent of biological weapons research conducted during the cold war (Alibek and Handelman 1999, Tucker 1999). Obviously, this concern has intensified since the tragedies of September 11, 2001 (Lawler 2001). Much attention has been directed toward the use of pathogenic microorganisms as biological weapons against humans, but there has been growing awareness of the potential use of microbes as weapons against crops as well (MacKenzie 1999, Rogers et al. 1999, Schaad et al. 1999,Yang and Sanogo 2000), especially in view of information that has come to light concerning Iraq’s past efforts to develop biological weapons against crop plants (Whitby and Rogers 1997). The impact of plant diseases on agriculture is immense. In the United States, for example, annual total losses due to crop diseases are estimated at over $30 billion, with 65% of that amount attributed to introduced (invasive) microbes (Pimentel et al. 2000). Economically important pathogens continue to be accidentally introduced, some with very large economic consequences (Bandyopadhyay et al. 1998, Gottwald et al. 2001).Although, to our knowledge, plant pathogens have never been deliberately introduced into US crops as an act of warfare or terrorism, there is concern that this and many other countries are vulnerable to such acts of aggression (Kadlec 1995, Horn and Breeze 1999, Pearson 1999). The chances of a given plant pathogen being used successfully as a biological weapon involve, among other things, ease of production, storage, and delivery, and then the fate of the introduced pathogen once it is introduced into a susceptible crop (Schaad et al. 1999). This article is concerned with assessing the risk of the latter, including accidentally introduced plant pathogens (Yang et al. 1991, Ruesink et al. 1995, Schmitz and Simberloff 1997, Enserink 1999), a key component of the Executive Order on Invasive Species (White House 1999b). The Animal and Plant Health Inspection Service (APHIS) of the US Department of Agriculture uses several