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

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.

Fig. 1

Behavioral response of female parasitoids to volatiles collected from teosinte with C. partellus eggs (exposed), without Chilo partellus eggs (non-exposed) and solvent control in a four-arm olfactometer bioassay. (a) response of Trichogramma bournieri; (b) response of Cotesia sesamiae. Each female parasitoid was observed for 12 min (N = 12). Bars followed by different letters are significantly different at P < 0.01

Fig. 2

A representative GC-EAG response of female Cotesia sesamiae to volatiles collected from Zea perennis with eggs. FID peaks marked are those which elicited antennal response in coupled runs: a = hexanal, b = 2,3-butanediol, c = (E)-2-hexenal, d = (Z)-3-hexen-1-ol, e = nonane, f = (Z)-2-heptenal, g = 6-methyl-5-heptene-2-one, h = (E,E)-2,4-heptadienal, i = limonene, j = (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), k = decanal, l = (E)-β-farnesene