Tritrophic Relationships Rebecca Martin Chemically Mediated

Plants, Pests, and the Parasitoids who Love them…  Tritrophic relationships are three way interactions  Plant chemical cues elicit natural enemies to ‘defend’ herbivore infested plants  Plants know when they are under attack. green leaf volatiles.  Mechanically damaged plants only emit green leaf volatiles. terpenoids.  Insect wounded plants emit various blends of terpenoids.  Parasitoids can differentiate between mechanically damaged and insect wounded plants.

Interesting considerations  How does a plant distinguish between a bite and a cut?  How do specialist parasitoids locate their particular host?  How do stage specific parasitoids find hosts of the right developmental stage?  Is this useful for biological control?

Examples of Chem. Mediated Tritrophic Relationships  Corn ( Zea mays )– Beet Armyworn ( S. exigua ) – C. marginiventris  Tobacco (N. attenuata) – Tobacco budworn (H. virescens) – C. nigriceps  Field elm (Ulmus minor) – Elm leaf beetle (X. luteola ) – O. gallerucae  Vicia fabia ( broad bean ) – T. urticae – P. persimilis Plant – Pest – Parasitoid

Cotesia marginiventris (Braconidae, Hymenoptera)  Native to Cuba and West Indies. Found throughout the US and South America  General parasitoid of Noctuid moths  Corn infested by beet armyworms Spodoptera exigua ( Noctuidae, Lepidoptera ) send out distress signals which attract C. marginiventris.  Volicitin from beet armyworm saliva initiates corn to synthesize and emit semiochemicals

Cardiochiles nigriceps (Braconidae, Hymenoptera)  Specialist parasitoid of tobacco budworm Heliothes virescens (Noctuidae, Lepidoptera).  Can differentiate between H. virescens and close relative corn earworn H. zea.  Tobacco plants emit different concentrations of various semiochemicals based on which species of herbivore is feeding.

Host specific recognition

Oomyzus gallerucae   Egg parasitoid of elm leaf beetle Xanthogaleruca luteola (Chrysomelidae, Coleoptera ).   Ovipositor wounding, not feeding, initiates plant chemical release.   Field elms emit a different chemical blend when fed on by elm leaf beetle.   O. gallerucae can differentiate between oviposition and feeding.   Have succesfully been employed in biological control. (Eulophidae, Hymenoptera)

Phytoseiulus persimilis  P. persimilis is used as biological control agent of two spotted spider mites Tetranychus urticae.  Bean plants infested with TSSM emit terpenoids and methyl saliclylate.  Important for biological control.

Conclusion  Tritrophic relationships involve complex chemical interactions.  Plants can differentiate between mechanical damage, insect wounding and even between pest species and types of damage.  Parasitoids and predators can recognize varying semiochemicals from different plants in different states of distress.  Chem. Mediated Tritrophic relationships can be implemented in biological control.  Everybody wins in THE END ! (except the pest ).

References  Wegener, R. et al. (2001). "Analysis of volatiles induced by oviposition of elm leaf beetle Xanthogaleruca luteola on Ulmus minor." Journal of Chemical Ecology 27(3).  Daly, H. (1998). Introduction to Insect Biology and Diversity. New York, Oxford University Press.  Turlings, T. et al. (1992). "Systemic release of chemical signals by herbivore injured corn." Proc. Natl. Acad. Sci. USA vol. 89.  Moraes, C. M. D. et al (1998). "Herbivore infested plants selectively attract parasitoids." Nature 393(6685).  McIntyre, J. The role of plants in attracting predators and parasitoids to control herbivore feeding, Colorado State University. Last visited: April 20, 2003  Kessler A., Baldwin T. (2002). "Plant - mediated tritrophic interactions and biological pest control." AgBiotechnet vol. 4.  Stotz, H. et al (1999). "Plant - Insect Interactions." Current Opinion in Plant Biology 2.  Hoballah, M. (2001). Benefits, costs and exploitation of caterpillar induced odor emissions in maize plants. Laboratory of Animal Ecology and Entomology, University of Neuchatel: 195.  Last visited May 5, 2003 Last visited May 5, 2003  Last visited May 6, 2003 Last visited May 6, 2003  Last visited May 5, 2003 Last visited May 5, 2003  Last visited Apr. 28, 2003 Last visited Apr. 28, 2003  Last visited May 1, 2003 Last visited May 1, 2003  Last visited May 1, 2003 Last visited May 1, 2003