Evolution of Soybean Aphid Biotypes: Understanding and Managing Virulence to Host-Plant Resistance

Abstract

The soybean aphid (Aphis glycines Matsumura) has rapidly become one of the most significant insect pests of soybean (Glycine max) worldwide (Ragsdale et al., 2007). The rise of soybean aphid in importance is in large part due to the invasion of North America ca. 2000, presumably coming from its native range in Asia (Ragsdale et al., 2004). In the first few years of the North American invasion, the soybean aphid spread across much of the NorthCentral US and the provinces of Ontario and Quebec. Its current distribution includes over 80% of the soybean growing region of the US and Canada (Vennette & Ragsdale, 2004). Worldwide, the distribution includes much of East Asia (China, Japan, The Philippines, South Korea, Indonesia, Malaysia, Thailand, Vietnam, and Russia), all of which likely represents the ancestral range (Footit et al., 2006). Options for management and control of soybean aphid are limited. As an alternative to chemical insecticides, host-plant resistance is a common method of aphid control (Van Emden, 2007), which uses plant hosts with genetically inherited traits that enable the plant to withstand pest attack better than a plant lacking these traits (Smith, 2005). Although soybean aphid resistant varieties have been studied in China (Wu et al., 2004), new soybean varieties have been developed with resistance to the soybean aphid specifically for use in North America (Hill et al., 2004, 2006a,b; Mian et al., 2008; Zhang et al., 2009; Hill et al., 2010). Varieties for North American commercial use were available for the first time in 2010. However, the host-plant resistance strategy is complicated because of rapid evolution of soybean aphid populations (i.e. biotypes) that have overcome host-plant resistance (i.e. virulence). Biotypes can be defined as “populations within an arthropod species that differ in their ability to utilize a particular trait in a particular plant genotype” (Smith, 2005). The presence of soybean aphid biotypes with virulence to host-plant resistance varieties before these varieties were commercially released suggests that the soybean aphid can rapidly adapt to these new lines and thereby threaten the effectiveness and sustainability of the host-plant resistance strategy.