Subterranean Volatile Increases Biological Control Figure 3. Effect of pregeijerene on mortality of Diaprepes abbreviatus larvae and associated attraction of entomopathogenic nematode infective juveniles (IJs) (all species combined). A) Average mortality of larvae buried with purified pregeijerene compared with the solvent control (N = 10, t = 4.01, P = 0.0008). B) Mean number of IJs recovered from cages containing purified pregeijerene compared with cages containing the solvent control (N = 10, t = 5.33, P = 0.00005). C) Mean number of IJs recovered from soil samples surrounding cages containing pregeijerene compared with the solvent control (N = 10, t = 5.67, P = 0.00003). doi:10.1371/journal.pone.0038146.g003 pathogens, living in a complex ecological food web in the soil [37]. Although induced plant responses were originally postulated as a potential novel approach to pest management in agricultural systems [38] for insect herbivore population regulation [39], few studies [40–43] of induced responses (particularly volatiles) have addressed their practical application beyond fundamental concepts in ecology and evolutionary biology [35,37,43], with particularly few studies for belowground systems. HIPVs are likely important mediators of tritrophic interactions that afford indirect plant defense within the root zone. Our study not only shows this PLoS ONE | www.plosone.org 4 June 2012 | Volume 7 | Issue 6 | e38146