Effects of elevated carbon dioxide and ozone on volatile terpenoid emissions and multitrophic communication of transgenic insecticidal oilseed rape (Brassica napus)

Abstract

Does transgenically incorporated insect resistance affect constitutive and herbivore-inducible terpenoid emissions and multitrophic communication under elevated atmospheric CO(2) or ozone (O(3))? This study aimed to clarify the possible interactions between allocation to direct defences (Bacillus thuringiensis (Bt) toxin production) and that to endogenous indirect defences under future climatic conditions. Terpenoid emissions were measured from vegetative-stage non-Bt and Bt Brassica napus grown in growth chambers under control or doubled CO(2), and control (filtered air) or 100 ppb O(3). The olfactometric orientation of Cotesia vestalis, an endoparasitoid of the herbivorous diamondback moth (Plutella xylostella), was assessed under the corresponding CO(2) and O(3) concentrations. The response of terpenoid emission to CO(2) or O(3) elevations was equivalent for Bt and non-Bt plants, but lower target herbivory reduced herbivore-inducible emissions from Bt plants. Elevated CO(2) increased emissions of most terpenoids, whereas O(3) reduced total terpenoid emissions. Cotesia vestalis orientated to host-damaged plants independent of plant type or CO(2) concentration. Under elevated O(3), host-damaged non-Bt plants attracted 75% of the parasitoids, but only 36.8% of parasitoids orientated to host-damaged Bt plants. Elevated O(3) has the potential to perturb specialized food-web communication in Bt crops.

Plant Volatile Organic Compounds (VOCs) in Ozone (O3) Polluted Atmospheres: The Ecological Effects

“…The ozonolysis of major herbivore-inducible VOCs did not affect the orientation of Cotesia vestalis (Haliday) (=Cotesia plutellae) towards cabbage plants (Brassica oleraecea) or oilseed rape (B. napus L.) damaged by Plutella xylostella L. -(Lepidoptera: Yponomeutidae) (Pinto et al 2007b;Himanen et al 2009). The orientation of the predatory mite P. persimilis towards herbivore-damaged Lima bean plants also was unaffected (Pinto et al 2007b).…”

“…To date, few laboratory experiments have been conducted to assess whether degradation of VOCs by O 3 can affect tritrophic interactions between plant, herbivore and herbivore natural enemies (Pinto et al 2007b, c;Himanen et al 2009). The ozonolysis of major herbivore-inducible VOCs did not affect the orientation of Cotesia vestalis (Haliday) (=Cotesia plutellae) towards cabbage plants (Brassica oleraecea) or oilseed rape (B. napus L.) damaged by Plutella xylostella L. -(Lepidoptera: Yponomeutidae) (Pinto et al 2007b;Himanen et al 2009).…”

Yeheb (Cordeauxia edulis) extract deters feeding and oviposition of Plutella xylostella and attracts its natural enemy

“…While the compounds for which we had standards were quantified readily in reference to the standards, those monoterpenes (MTs) for which we lacked standards were tentatively quantified by relating their peak areas to a-pinene assuming their responses would be the same as that of a-pinene. Similarly (E)-b-farnesene was used to tentatively quantify those sesquiterpenes (SQTs) for which we lacked pure standards (Himanen et al 2009). …”

“…Larval feeding was monitored for 48 h. After 48 h, the final average weight of the two larvae was recorded and weight gain (WG) was determined using the formula, (Ln(w f ) -Ln(w i ))/d, where w f is final weight, w i is initial weight and d is number of days feeding (Ibrahim et al 2005). Immediately after the experiment, leaves were scanned and the feeding damaged area was determined with Adobe Photoshop software (Adobe Systems Incorporated, Wilmington, DE, USA) (Himanen et al 2009). …”

Soybean (Glycine max) plants genetically modified to express resistance to glyphosate: can they modify airborne signals in tritrophic interactions?

“…Genetic manipulation of a particular trait may affect others as a result of possible pleiotropy or insertional mutations (Schuler et al 1999). During the last few years several studies have focused on the impact of the Bt gene on plant VOC emissions, and the possible effects on herbivores and carnivores (Yan et al 2004;Turlings et al 2005;Dean and De Moraes 2006;Himanen et al 2009). More recently, a few studies have also assessed the effects of plants engineered to express resistance to Venturia inaequalis, a causal agent of apple scab disease, on volatile induction and the response of a parasitoid to herbivore-induced VOCs (Vogler et al 2009(Vogler et al , 2010.…”