Host selection by Ibalia leucospoides based on temporal variations of volatiles from the hosts? fungal symbiont

N. JOFRE; M. B. PILDAIN; A. M. CIRIGLIANO; G. M. CABRERA; J. C. CORLEY; A. S. MARTÍNEZ

JOURNAL OF APPLIED ENTOMOLOGY

Blackwell Verlag GmbH

Año: 2016

0044-2240

Insect parasitoids locate hosts via reliable and predictable cues such asvolatile emissions from hosts and/or host plants. For insects that dependon mutualistic organisms, such as many wood-boring insects, symbiontderivedsemiochemicals may represent a source of such cues to beexploited by natural enemies. Ultimately, exploitation of these signalsmay increase fitness by optimizing foraging efficiency. Female parasitoidsof Ibalia leucospoides use volatiles from the fungal symbiont Amylostereumareolatum of their host Sirex noctlio to find concealed host eggs and younglarvae within the xylem. We hypothesize that the temporal pattern offungal emissions may indicate not only the presence of host larvae butalso be used as a cue that indicates host suitability and age. Such informationwould allow female parasitoids to discern more efficiently betweenhosts within ovipositor reach from those already buried too deep into thexylem and out of reach. In this context, we assessed the behaviour ofI. leucospoides females to volatiles of A. areolatum in a ?Y?-tube olfactometerat regular intervals over 30 days. We concurrently examined the fungalvolatiles by headspace sampling through solid-phase microextraction(SPME) followed by gas chromatography mass spectrometry (GC-MS).We observed that females were attracted to volatiles produced by twoweek-old fungal cultures, a period that matches when older larvae are stillwithin ovipositor reach. Four chemical compounds were detected: ethanol,acetone, acetaldehyde and the sesquiterpene 2,2,8-trimethyltricyclo[6.2.2.01,6]dodec-5-ene, with each compounds? relative abundancechanging over time. Results are discussed in the context of parasitoids fitness.Future studies involving electrophysiology, different collection techniquesand further behavioural assays will help in identifying thecompounds that convey temporal information to female parasitoids andhave the potential for being used in integrated pest managementprogrammes.