Synthetic feeding stimulants enhance insecticide activity against western corn rootworm larvae, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae)

The western corn rootworm, Diabrotica virgifera virgifera LeConte, continues to be a significant pest of corn (Zea mays L.) in the United States. Because of recent changes in their distribution (now in Europe; Kiss et al. 2005) the impact of this pest is growing. While a variety of management tools are still available for growers, some of the current options including crop rotation (Gray et al. 2009), baits to control adults (Tollefson 1998), insecticidal seed treatments (Furlan et al. 2006), Bt corn (Lefko et al. 2008; Meihls et al. 2008), adult sprays (Meinke et al. 1998) and granular soil insecticides (Wright et al. 2000) have issues reducing their effectiveness or do not work in certain areas. For this reason, it is worthwhile to look towards the development of new strategies that are specifically aimed at improving the efficacy of current products. We previously demonstrated the presence of phagostimulation cues for western corn rootworm larvae in the roots of corn plants. In behavioural bioassays, neonate larvae fed vigorously on paper disks treated with liquid pressed from corn roots, or with a solvent extract of corn roots, but not on disks treated with distilled water (Bernklau and Bjostad 2005). In the same study, the efficacy of a neonicotinoid insecticide (thiamethoxam; Syngenta, Inc., Basel, Switzerland) was significantly increased when crude corn root extract was added. The concentration of