GC-EAG-analysis of volatiles from Brussels sprouts plants damaged by two species of Pieris caterpillars: olfactory receptive range of a specialist and a generalist parasitoid wasp species

Abstract

Feeding by Pieris brassicae or P. rapae caterpillars on Brussels sprouts plants induces the emission of synomones that attract natural enemies of the caterpillars, Cotesia glomerata, a generalist parasitoid, and C. rubecula, a specialist on P. rapae. Previous research on this tritrophic system has identified a large number of volatiles in the headspace of herbivore-damaged Brussels sprouts plants, and this paper addresses the question which of these volatiles are perceived by the two parasitoid species. Headspace odors from both P. brassicae-and P. rapae-damaged Brussels sprouts plants were analyzed by coupled gas chromatography electroantennogram (GC-EAG) detection. Twenty volatiles evoked consistent EAG reactions in the antennae of both species and nineteen of these volatiles could be identified with GC-MS. One component that could not be identified due to its low concentration, evoked EAG responses in antennae of C. rubecula only. Possible consequences for searching behavior of the two parasitoid species are discussed.Key words. Lepidoptera -Pieridae -HymenopteraBraconidae -Cotesia glomerata -Cotesia rubeculaBrussels sprouts -Brassicae oleracea -GC-EAG -tritrophic interactions -specialist -generalist M a terials and methods Plants and InsectsPlants (Brussels sprouts, Brassica oleracea L. var gemmifera, cv Icarus), were grown in a greenhouse at 20-26°C, 50-70% r.h. and a L16:D8 photoregime. Herbivores (Pieris brassicae and P. rapae)

Variation In Plant Volatiles and Attraction Of The ParasitoidDiadegma semiclausum(Hellén)

“…The odor blend of infested Brussels sprout was similar to that of uninfested Brussles sprout, but many of the compounds were emitted in higher amounts by infested plants, which was in line with findings of other studies (Blaakmeer et al, 1994;Geervliet et al, 1997;Reddy and Guerrero, 2000;Smid et al, 2002). Compounds like (Z)-3-hexen-1-yl acetate, (Z)-3-hexen-1-ol, and limonene, which were also detected in our samples, could play a role in the attraction of the parasitoids C. rubecula, C. glomerata, and C. plutellae, and of the predatory lacewing Chrysoperla carnea (Geervliet et al, 1997;Reddy et al, 2002;Smid et al, 2002). The volatile profile of Plutella-infested Brussels sprout shares many similarities with the odor profiles from white cabbage and Brussels sprout infested by different Pieris spp.…”

“…These compounds play a role in the host searching behavior of parasitoid species that forage on hosts associated with plants of this family (Read et al, 1970(Read et al, , 1985Shiojiri et al, 2001;Smid et al, 2002). Other studies show effects of inter-and intraspecific variation in volatiles of cruciferous plants on their attractivity to parasitoids (Geervliet et al, 1996;Liu and Jiang, 2003;Kalule and Wright, 2004).…”

Antennal Electrophysiological Responses of Three Parasitic Wasps to Caterpillar-Induced Volatiles from Maize (Zea mays mays), Cotton (Gossypium herbaceum), and Cowpea (Vigna unguiculata)

“…This confirms the difficulty of detecting any differences in peripheral perception among parasitoids. As observed for the parasitoids in the present study, C. glomerata and C. rubecula show a broad olfactory capability responding to 20 compounds in the cabbage volatiles (Smid et al, 2002). The wasps' ability to detect a wide range of compounds in the induced odors of maize, cotton, and cowpea plants suggests that they use a wide range of compounds to identify plants that carry hosts.…”

“…No obvious differences were found in the detected range of compounds released by Brussels sprouts when attacked by caterpillars (Smid et al, 2002). This confirms the difficulty of detecting any differences in peripheral perception among parasitoids.…”

“…Pettersson et al (2000) found that the bark beetle parasitoid, Rotrocerus xylophagum (Hymenoptera: Pteromilidae), did not respond to the major compounds present in the bark oil. More recently, Smid et al (2002) compared the responses of a specialist and generalist parasitoid of Pieris caterpillar to attacked Brussels sprouts, and showed that the two parasitoid species responded similarly to a large number of compounds present in the odor of damaged plants. Interestingly, two compounds were only perceived by the specialist parasitoid (Cotesia rubecula) (Smid et al, 2002).…”