The effects of barley plant volatiles on host selection behaviors of wheat stem sawfly, Cephus cinctus Norton

Wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), causing serious economic damage in cereals grown across western North America. Integrated pest management centered on plant resistance is the best option to manage this pest. Plant resistance can have a range of effects on the pest. The effects can be lethal or simple deterrence against use of the host plant. Female C. cinctus readily oviposit in a wide range of host plants irrespective of larval survival rates; for example, larvae do not survive in oat and have lower survival in barley compared to wheat. Thus, a question arises whether female host selection is governed by host plant volatiles. To evaluate this question, we selected two barley cultivars: ‘Hockett’ and ‘Craft.’ These cultivars differ significantly in C. cinctus infestation and larval survival rates. In this study, we compared volatile organic compounds from these cultivars and further compared host selection behavior using a Y-tube olfactometer. We used plants at the Zadoks 34 growth stage, which have at least one internode suitable for C. cinctus oviposition. Our results indicate that the amount of (Z)-3 hexenyl acetate (a known attractant) was greater in ‘Hockett’ while linalool (a putative defense compound) was greater in ‘Craft.’ Y-tube olfactometer assays indicated that females chose ‘Hockett’ over ‘Craft’ in choice trials. These results suggest we can manipulate host plant traits governing volatile emissions in developing barley to potentially divert - or attract - C. cinctus to specific cultivars.