Subterranean, Herbivore-Induced Plant Volatile Increases Biological Control Activity of Multiple Beneficial Nematode Species in Distinct Habitats

Abstract

While the role of herbivore-induced volatiles in plant-herbivore-natural enemy interactions is well documented aboveground, new evidence suggests that belowground volatile emissions can protect plants by attracting entomopathogenic nematodes (EPNs). However, due to methodological limitations, no study has previously detected belowground herbivore-induced volatiles in the field or quantified their impact on attraction of diverse EPN species. Here we show how a belowground herbivore-induced volatile can enhance mortality of agriculturally significant root pests. First, in real time, we identified pregeijerene (1,5-dimethylcyclodeca-1,5,7-triene) from citrus roots 9–12 hours after initiation of larval Diaprepes abbreviatus feeding. This compound was also detected in the root zone of mature citrus trees in the field. Application of collected volatiles from weevil-damaged citrus roots attracted native EPNs and increased mortality of beetle larvae (D. abbreviatus) compared to controls in a citrus orchard. In addition, field applications of isolated pregeijerene caused similar results. Quantitative real-time PCR revealed that pregeijerene increased pest mortality by attracting four species of naturally occurring EPNs in the field. Finally, we tested the generality of this root-zone signal by application of pregeijerene in blueberry fields; mortality of larvae (Galleria mellonella and Anomala orientalis) again increased by attracting naturally occurring populations of an EPN. Thus, this specific belowground signal attracts natural enemies of widespread root pests in distinct agricultural systems and may have broad potential in biological control of root pests.

Terpenoids in plant and arbuscular mycorrhiza-reinforced defence against herbivorous insects

“…Terpenes are the most prominent VOCs emitted from below-ground tissues (Rasmann et al, 2005;Ali et al, 2011;Palma et al, 2012;Peñuelas et al, 2014), and among these sesquiterpenes are the compounds that show the greatest diffusion in the soil (Hiltpold and Turlings, 2008). Terpenoids have been shown to play a crucial role in the specificity of below-ground tritrophic interactions (Rasmann and Turlings, 2008).…”

Vertical T-maze Choice Assay for Arthropod Response to Odorants

“…Typically, one arm of such a Y-tube will receive a treatment odorant, while the other will be left blank 13 . Variations on such olfactometers may include addition of multiple radiating arms 14 and even addition of a soil medium for assaying the behavior of organisms moving through soil 15 . In developing such olfactometers and associated assays, it is important to consider how closely natural conditions are replicated and thus the true relevance of the assessed…”

Volatile terpenoids: multiple functions, biosynthesis, modulation and manipulation by genetic engineering

“…Terpenoids are also involved in the plant-plant interaction, repelling pests and attracting enemies of pests (Unsicker et al 2009). Volatile terpenoids are involved especially in attracting pollinators, seed dispersal, defense against herbivores from both below-and above-ground (Ali et al 2012;Delory et al 2016), plant-plant signaling and protection against pathogens (Huang et al 2012) (Fig. 2).…”