Evolutionary mismatch in oviposition preference and larval survival of Cephus cinctus (Hymenoptera: Cephidae) in smooth brome: A potential trap crop for spring wheat

Wheat stem sawfly (WSS), Cephus cinctus Norton (Hymenoptera: Cephidae), is a major pest of wheat in the Northern Great Plains of North America. Smooth brome (Bromus inermis Leyss) was suggested as a potential trap crop around wheat fields. However, there was a lack of knowledge on WSS host preference behavior for oviposition in wheat and smooth brome. So, to fill this research gap, we compared female WSS host-selection behavior, oviposition preferences, and subsequent larval survival in spring wheat and smooth brome in greenhouse and field studies. We found greater WSS infestation, more parasitism, and no survival in smooth brome compared to wheat in the field. WSS preferred the volatiles emitted by smooth brome over wheat, as evidenced by the Y-tube olfactometer study. We analyzed the volatile organic compounds collected from smooth brome and spring wheat and found a greater amount of key behaviorally active compounds used by female WSS, (Z)-3-hexenyl acetate and β-ocimene. There were also a greater number of eggs in smooth brome relative to wheat, with no difference in the proportion of infested stems in choice tests conducted for two days at Zadoks 49 in cage trials. Our findings support the consideration of smooth brome for use in trap cropping in spring wheat fields to improve integrated pest management strategies for WSS.