Host selection by the wheat stem sawfly in winter wheat and the role of semiochemicals mediating oviposition preference

Abstract

The wheat stem sawfly (WSS), Cephus cinctus Norton (Hymenoptera: Cephidae), causes significant damage in cereal crops in the northern Great Plains of North America. This study assessed oviposi- tion preference in winter wheat, Triticum aestivum L. (Poaceae), and investigated how it is affected by the emission of semiochemicals, with the overall goal of enhancing trap crop efficacy.We studied five winter wheat cultivars that could be recommended as trap crops for WSS and compared them with regards to agronomic characteristics influencing oviposition behavior and their emission of behaviorally active volatiles. Subsequently, we evaluated oviposition preference on three selected cultivars, Norstar, Neeley, and Rampart, using choice tests at two plant growth stages. Most eggs were found in Norstar at both stages tested when females were exposed to the three cultivars simulta- neously making it the preferred choice for a trap crop. Norstar also emitted more behaviorally active volatiles, primarily (E)- and (Z)-b-ocimene. The role of main stem height or diameter in oviposition was inconsistent for infested vs. uninfested stems within cultivars, although there was a correlation between infestation and height for younger plants. These results show that these agronomic charac- teristics, typically viewed as explanatory, did not clearly explain oviposition preference and suggest a role of b-ocimene in determining suitability for oviposition among these cultivars. This study supports previous findings suggesting oviposition preference in winter wheat involves several cues, including stem height and volatile attractants that may be important in determining suitability.