Olfactory attraction of a parasitoid to plants infested with host butterfly eggs.

CASTELO, M.K.; VAN NOUHUYS, S.; CORLEY, J.C.

JOURNAL OF INSECT SCIENCE

University of Wisconsin Libraries

Lugar: Wisconsin; Año: 2010 vol. 10 p. 1 - 16

1536-2442

Parasitoids locate inconspicuous hosts in a heterogeneous habitat using plant volatiles, some of which are induced by the host. Hyposoter horticola is a parasitoid of the Glanville fritillary butterfly Melitaea cinxia. The butterfly lays eggs in clusters on leaves of Plantago lanceolata and Veronica spicata. The parasitoid oviposits into neonate host larvae that have not yet broken out of the eggshell. Thus, though H. horticola is a parasitoid of herbivorous larvae, it must find host eggs on undamaged plants. Using a Y-tube olfactometer, we tested the response of wasps to odors of hosts and extracts of the attacked plant species. We found that three week-old eggs (near hatching) were attractive to young wasps while one week-old eggs were attractive only to old or experienced ones. Host larvae were not attractive. Plantago lanceolata was attractive as a water extract, but not in ethanol or hexane. Veronica spicata was attractive only if harboring host eggs. We then presented free flying H. horticola in a large outdoor enclosure with host and plant cues. As in the olfactometer, V. spicata was attractive only with eggs on it, and P. lanceolata was somewhat attractive with or without eggs. This study shows for the first time that a larval parasitoid uses egg or oviposition induced plant volatiles to find hosts, and that butterfly eggs or traces of oviposition induce these volatiles. Based on the results, and given the natural distribution of the plants and hosts, we would expect parasitism of hosts on P. lanceolata to be low. Instead, under natural conditions a fraction of the eggs in virtually all egg clusters is parasitized on both plant species. We discuss from the mismatch of our experimental results with the natural pattern of host-parasitoid interactions in terms of the expected coupling foraging cues with foraging success.