Manipulating native populations of entomopathogenic nematodes with herbivore induced plant volatiles to enhance pest control

Aboveground mulitrophic interactions such as the attraction of natural enemies of herbivores to herbivore induced plant volatiles (HIPVs) have been extensively investigated. Recently, analogous HIPV mediated interactions below ground have been described for corn as well as for citrus seedlings damaged by root weevils. The HIPVs released by damaged citrus roots attract a plurality of entomopathogenic nematodes (EPNs) and its main constituent was identified as pregeijerene (1, 5-dimethylcyclodeca-1, 5, 7-triene). Release of this HIPV by citrus roots peaked 9-12 hr after initiation of larval Diaprepes abbreviates root feeding. In field assays, lab-collected citrus root HIPVs attracted native EPNs and increased mortality of beetle larvae compared with controls. In addition, field applications of 8ng/µl of pregijerene isolated from Ruta graveolens caused similar results. Field collections of root volatiles from mature citrus trees proved that pregeijerene is released in the field in response to herbivore damage. Using species-specific probes designed to identify EPN species, we determined by quantitative real-time PCR that field application of pregeijerene increased pest mortality by attracting four species of EPNs native to Florida, U.S.A. The current investigation identifies in real-time a specific belowground cry for help released by citrus roots that attracts natural enemies of a polyphagous root pest. The unusual 12 carbon terpene pregeijerene, or its thermal breakdown product geijerene, has been found in root extracts of several plants but an ecological role of this natural plant product has not been described previously. This and similar chemicals may have broad application for controlling agriculturally significant root pests.