Responses of parasitoids to volatiles induced by Chilo partellus oviposition on teosinte, a wild ancestor of maize.

Daniel M. Mutyambai,Christine M. Woodcock,Johnnie Van Den Berg,John C. Caulfield,John A. Pickett,Charles A. O. Midega,Toby J. A. Bruce,Zeyaur R. Khan

doi:10.1007/s10886-015-0570-1

Abstract

Maize, a genetically diverse crop, is the domesticated descendent of its wild ancestor, teosinte. Recently, we have shown that certain maize landraces possess a valuable indirect defense trait not present in commercial hybrids. Plants of these landraces release herbivore-induced plant volatiles (HIPVs) that attract both egg [Trichogramma bournieri Pintureau & Babault (Hymenoptera: Trichogrammatidae)] and larval [Cotesia sesamiae Cameron (Hymenoptera: Braconidae)] parasitoids in response to stemborer egg deposition. In this study, we tested whether this trait also exists in the germplasm of wild Zea species. Headspace samples were collected from plants exposed to egg deposition by Chilo partellus Swinhoe (Lepidoptera: Crambidae) moths and unexposed control plants. Four-arm olfactometer bioassays with parasitic wasps, T. bournieri and C. sesamiae, indicated that both egg and larval parasitoids preferred HIPVs from plants with eggs in four of the five teosinte species sampled. Headspace samples from oviposited plants released higher amounts of EAG-active compounds such as (E)-4,8-dimethyl-1,3,7-nonatriene. In oviposition choice bioassays, plants without eggs were significantly preferred for subsequent oviposition by moths compared to plants with prior oviposition. These results suggest that this induced indirect defence trait is not limited to landraces but occurs in wild Zea species and appears to be an ancestral trait. Hence, these species possess a valuable trait that could be introgressed into domesticated maize lines to provide indirect defense mechanisms against stemborers.

Highlights

Emission of herbivore-induced volatiles (HIPVs) in response to herbivore feeding damage has been studied intensively during the past two decades
Behavioral Responses of Parasitoids to Headspace Samples of Volatile Organic Compound (VOC) Female T. bournieri individuals spent significantly more time in olfactometer arms containing volatiles from plants exposed to oviposition in comparison to those with volatiles from plants without eggs and solvent controls, for four of the five teosinte species
Our findings provide evidence that indirect defense involving insect egg-induced herbivore-induced plant volatiles (HIPVs) emission is an ancestral trait in maize, present in several species of teosinte

Summary

Introduction

Emission of herbivore-induced volatiles (HIPVs) in response to herbivore feeding damage has been studied intensively during the past two decades. A relatively small but growing number of investigations have revealed that oviposition can induce production of plant volatiles that attract parasitoids (Bruce et al 2010; Colazza et al 2004; Fatouros et al 2012; Hilker and Meiners 2006; Tamiru et al 2011, 2012). Detection of egg deposition and subsequent changes in chemical phenotype prepares plants for the impending attack by emerging phytophagous larvae (Bruce et al 2010; Hilker et al 2002). Information regarding variability in HIPV emission comes mainly from studies of cultivated plants (Gouinguené et al 2001; Krips 2000; Takabayashi et al 1991; Turlings et al 1998). Studies of wild systems include a wild cotton variety that was found to release much higher quantities of induced volatiles than cultivated varieties (Loughrin et al 1995), and

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