Olfactory attraction of the larval parasitoid, Hyposoter horticola, to plants infested with eggs of the host butterfly, Melitaea cinxia

Marcela K. Castelo1a*, Saskya van Nouhuys2b, and Juan C. Corley3c

1CONICET - Grupo de Investigación en Ecofisiología de Parasitoides - Departamento de Ecología, Genética y Evolución - Facultad de Ciencias Exactas y Naturales - Universidad de Buenos Aires, Ciudad Universitaria, Pabellón II, (C1428EHA) Ciudad de Buenos Aires, Argentina
2Department of Biological and Environmental Sciences, Division of Population Biology, PO Box 65, FIN, University of Helsinki, Finland and Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, USA
3CONICET - Laboratorio de Ecología de Insectos - INTA Bariloche, (R8400HRG) Bariloche, Río Negro, Argentina

Abstract

Parasitoids locate inconspicuous hosts in a heterogeneous habitat using plant volatiles, some of which are induced by the hosts. Hyposoter horticola Gravenhost (Hymenoptera: Ichneumonidae) is a parasitoid of the Glanville fritillary butterfly Melitaea cinxia L. (Lepidoptera: Nymphalidae). Melitaea cinxia lays eggs in clusters on leaves of Plantago lanceolata L. (Lamiales: Plantaginaceae) and Veronica spicata L. (Lamiales: Plantaginaceae). The parasitoid oviposits into host larvae that have not yet hatched from the egg. Thus, though H. horticola is a parasitoid of Melitaea cinxia larvae, it must find host eggs on plants that have not been fed on by the larvae. Using a Y-tube olfactometer, the response of H. horticola to odors of Melitaea cinxia and extracts of the attacked plant species were tested. Three week-old eggs (near hatching) were attractive to young H. horticola, but one week-old eggs were attractive only to old or experienced H. horticola. Melitaea cinxia larvae were not attractive. A water extract of P. lanceolata was attractive, but ethanol or hexane extracts were not. None of the extracts of V. spicata were attractive. Leaves of V. spicata were attractive only if harboring eggs, but P. lanceolata leaves with eggs were not. Free flying H. horticola in a large outdoor enclosure were presented with host and plant cues. As in the olfactometer, V. spicata was attractive only when eggs were on it, and P. lanceolata was somewhat attractive with or without eggs. This study shows for the first time that a parasitoid of larvae uses egg volatiles or oviposition-induced plant volatiles, to find host larvae, and that Melitaea cinxia eggs or traces of oviposition induce the production of these volatiles by the plant. Based on the results, and given the natural distribution of the plants and M. cinxia eggs, parasitism of Melitaea cinxia eggs on P. lanceolata would be expected to be low. Instead, under natural conditions, a fraction of the eggs in virtually all egg clusters are parasitized on both plant species. The mismatch between the experimental results and the natural pattern of host-parasitoid interactions is discussed in terms of the expected coupling foraging cues with foraging success.

Keywords: chemical cues, foraging behavior, insect-plant interactions, multitrophic level interaction, Plantago lanceolata, Veronica spicata

Correspondence: a*mcastelo@ege.fcen.uba.ar, bsdv2@cornell.edu, cjcorley@bariloche.inta.gov.ar *Corresponding author

Received: 9 January 2009 | Accepted: 20 April 2009 | Published: 4 June 2010

ISSN: 1536-2442 | Volume 10, Number 53

Castelo MK, van Nouhuys S, Corley JC. 2010. Olfactory attraction of the larval parasitoid, Hyposoter horticola, to plants infested with eggs of the host butterfly, Melitaea cinxia. Journal of Insect Science 10:53, available online: insectscience.org/10.53


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