Identifying chemical repellents for wheat stem sawfly: Insights from host plant volatile analysis

The wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae) is a major pest in wheat, Triticum aestivum L., production in the Northern Great Plains of the United States. Cephus cinctus females oviposit eggs inside of stems, where the developing larvae feed and consequently decrease yields. Multiple females may oviposit into the same stem, but because larvae are cannibalistic, only one will survive. Oviposition is influenced by a combination of external factors, including host plant location via chemical cues. This study aimed to investigate the chemical interactions between C. cinctus and wheat by identifying the volatile organic compounds (VOCs) emitted by plants at specific growth stages. Two spring wheat varieties (Dagmar and Vida) were tested in this study. Volatiles were collected from plants at two growth stages: Stem elongation, when plants are susceptible to C. cinctus oviposition, and mid-heading, when plants are less suitable for C. cinctus development. Moreover, VOCs were collected from C. cinctus-infested and not infested plants. Experiments were conducted in the greenhouse under controlled environmental conditions. Volatiles were collected using a push-pull volatile collection system. After collection, samples were analyzed using coupled gas chromatography-mass spectrometry (GC-MS). Compounds were identified through comparison with spectra in the NIST mass spectral library. Preliminary results showed differences in VOC concentrations between varieties and growth stages. The results of this study will contribute to the long-term research of developing chemical repellents against wheat stem sawfly.