Identification of Key Plant-Associated Volatiles Emitted by Heliothis virescens Larvae that Attract the Parasitoid, Microplitis croceipes: Implications for Parasitoid Perception of Odor Blends
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Herbivores emit plant-associated volatile organic compounds (VOCs) after feeding on plants. These plant-associated VOCs can be used by parasitoids to locate their hosts. It is hypothesized that certain compounds play key roles in the attractiveness of host-associated odor blends. The larval parasitoid, Microplitis croceipes (Hymenoptera: Braconidae) and its herbivore host, Heliothis virescens (Lepidoptera: Noctuidae), a major pest of cotton plant were used as model species to identify key compounds mediating attraction of parasitoids to hosts. Comparative GC/MS analyses of cotton-fed vs. artificial diet-fed hosts indicated that 12 of 17 compounds in the headspace of H. virescens larvae were exclusive to plant-fed hosts, and thus considered to be plant-associated. In order to identify key attractive compounds, a full blend of 15 commercially available synthetic compounds was modified by removing each of the 10 plant-associated compounds emitted by host larvae. In Y-tube olfactometer bioassays testing parasitoid responses to modified blends, 1-octen-3-ol, decanal, (E)-β-caryophyllene, α-humulene, α-farnesene, and β-pinene were identified as key compounds contributing to attractiveness of the natural blend of VOCs emitted by cotton-fed hosts. The results showed that while various host-associated compounds act in concert to serve as useful host location cues, only a fraction of the natural blend mediates attraction in parasitoids. Furthermore, the role of a compound is better assessed in the context of other compounds, and odor blends are better perceived as a whole rather than as individual components.
KeywordsOlfactometer Gas chromatography-mass spectrometry Contextual perception Background odors
We thank Savannah Duke and Lindsay MacMillan for rearing the insects used for this study. This study was supported by Auburn University and the Alabama Agricultural Experiment Station.
- Fürstenberg-Hägg J, Zagrobelny M, Bak S (2013) Plant defense against insect herbivores. Int J Mol Sci 14:10242–10297Google Scholar
- Magalhães DM, Borges M, Laumann RA, Sujii ER, Mayon P, Caulfield JC, Midega CAO, Khan ZR, Pickett JA, Birkett MA, Blassioli-Moraes MC (2012) Semiochemicals from herbivory induced cotton plants enhance the foraging behavior of the cotton boll weevil, Anthonomus grandis. J Chem Ecol 38:1528–1538CrossRefPubMedGoogle Scholar
- Molnár BP, Tóth Z, Fejes-Tóth A, Dekker T, Kárpáti Z (2015) Electrophysiologically-active maize volatiles attract gravid female european corn borer. Ostrinia nubilalis J Chem Ecol:997–1005Google Scholar
- Ngumbi E, Fadamiro H (2012) Species and sexual differences in behavioural responses of a specialist and generalist parasitoid species to host-related volatiles. Bull Entomol Res 102:710–718Google Scholar
- Wajnberg É, Haccou P (2008) Statistical tools for analyzing data on behavioral ecology of insect parasitoids. In: Wajnberg É, Bernstein C, van Alphen J (eds) Behavioral ecology of insect parasitoids: from theoretical approaches to field. Blackwell Publishing Ltd, Oxford, UK, pp. 402–429CrossRefGoogle Scholar
- Zebelo S, Piorkowski J, Disi J, Fadamiro H (2014) Secretions from the ventral eversible gland of Spodoptera exigua caterpillars activate defense-related genes and induce emission of volatile organic compounds in tomato, Solanum lycopersicum. BMC Plant Biol 14:140CrossRefPubMedPubMedCentralGoogle Scholar