Courtship behavior and identification of a sex pheromone in Ibalia leucospoides (Hymenoptera: Ibaliidae), a larval parasitoid of Sirex noctilio (Hymenoptera: Siricidae)

Hajar Faal; Peter J Silk; Peter D Mayo; Stephen A Teale

doi:10.7717/peerj.12266

Courtship behavior and identification of a sex pheromone in Ibalia leucospoides (Hymenoptera: Ibaliidae), a larval parasitoid of Sirex noctilio (Hymenoptera: Siricidae)

PeerJ. 2021 Nov 4:9:e12266. doi: 10.7717/peerj.12266. eCollection 2021.

Authors

Hajar Faal^{1

2}, Peter J Silk³, Peter D Mayo³, Stephen A Teale¹

Affiliations

¹ Department of Environmental and Forest Biology, State University of New York-Environmental Science and Forestry, Syracuse, NY, USA.
² Forest Pest Methods Laboratory (Otis Laboratory), USDA-APHIS-PPQ-CPHST, Buzzards Bay, MA, United States of America.
³ Natural Resources Canada, Atlantic Forestry Centre, Fredericton, New Brunswick, Canada.

Abstract

Background: Ibalia leucospoides (Hymenoptera: Ibaliidae) is a larval parasitoid that has been widely introduced as a biological control agent for the invasive woodwasp,Sirex noctilio (Hymenoptera: Siricidae) in the Southern Hemisphere. In this study, the courtship behavior and identificaion of sex pheromones are described for I. leucospoides under laboratory conditions.

Methods: For courtship behavior, both sexes were observed in a wire mesh observation cylinder (75 cm length ×10 cm diameter) for 15 minutes. The female body washes were analyzed using Gas Chromatography- Electroantennographic Detection (GC-EAD). Then the EAD-active compounds were tentatively identified using GC-Mass Spectrometry (GC-MS) and examined in olfactometer assays.

Results: The courtship behavior included rhythmic lateral movements, mounting, head-nodding cycles in males, and wing-fanning in females. GC-EAD analysis of female body washes with male antennae revealed seven compounds which elicited antennal responses, four of which are straight-chain alkanes (C₂₃, C₂₅, C₂₆, and C₂₇). The identities of these alkanes were confirmed by matching the retention times, mass spectra, and male antennal activity to those of commercially obtained chemicals. In olfactometer assays, a blend of the four straight-chain alkanes was attractive to I. leucospoides males, and there was no response to blends that lacked any of these four compounds. Female body wash was no more attractive than the four-component blend. The ratios of EAD-active components differ between hydrocarbon profiles from males and females.

Conclusion: This study is the first investigation of cuticular hydrocarbons in the family Ibaliidae. It provides evidence that the ubiquitous alkanes (C₂₃, C₂₅, C₂₆, and C₂₇) in sex-specific ratios attract I. leucospoides males.

Keywords: Courtship behavior; Cuticular hydrocarbon; Ibaliidae; Parasitoid; Sex pheromone.

Grants and funding

This work was supported by the U.S. Forest Service grant no. 12DG11420004168 to Stephen A. Teale and the USDA-CSRS McIntire-Stennis Cooperative Forestry Program grant no. 32100061020832100 to Stephen A. Teale. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.