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 oviposition 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 simultaneously making it the preferred choice for a trap crop. Norstar also emitted more behaviorally active volatiles, primarily (E)-and (Z)-b-ocimene. The results for the effect of main stem height or diameter on oviposition was inconsistent between infested vs. uninfested stems within cultivars, although there was a correlation between infestation and height for younger plants. These results show that these agronomic characteristics, 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.

Farming system and wheat cultivar affect infestation of, and parasitism on, Cephus cinctus in the Northern Great Plains

“…Cephus cinctus has the ability to utilize both spring and winter wheat, and Montana has a large proportion of land planted to either winter or spring wheat, which is unique among neighboring states and provinces that experience recurring losses caused by C. cinctus . In our study, winter wheat in conventional fields had the highest rates of infestation and proportion of wheat stems cut by C. cinctus , which partially reflects a preference for the larger and more succulent stems of winter wheat . The greater C. cinctus injury in winter wheat relative to spring wheat could also reflect climate warming in the Northern Great Plains, causing a greater phenological synchrony between winter wheat and C. cinctus .…”

“…Cephus cinctus was known originally from native grasses and subsequently from spring wheat shortly after this crop was commonly planted . Reports that this pest also utilizes winter wheat cultivars, which are planted on a large proportion of arable land in Montana, are much more recent . As a consequence of the warming climate in the Northern Great Plains, there may be changes in seasonal phenology of C. cinctus as well as in agronomic practices used to grow spring and winter wheat crops.…”

“…5 Reports that this pest also utilizes winter wheat cultivars, which are planted on a large proportion of arable land in Montana, are much more recent. 14,15 As a consequence of the warming climate in the Northern Great Plains, 16 there may be changes in seasonal phenology of C. cinctus as well as in agronomic practices used to grow spring and winter wheat crops. However, we lack evidence for a better phenological synchrony between C. cinctus and winter wheat.…”

Preference–performance in a specialist sawfly on congeneric host plants

“…Other sawfly species use secondary metabolites in the selection of their host plant, such as Euura amerinae (L.) and Euura lasiolepis Smith, monophagous species that recognize and select their Salix host plants based on characteristic phenolic glycosides (Kolehmainen, ; Roininen et al., ). Host plant parameters not considered in the present study – such as leaf hardness, leaf surface, and plant volatiles – may also affect sawfly oviposition preferences (Buteler & Weaver, ; Braccini et al., ; Varella et al., ). They deserve further investigation in our study system.…”

Increased area of a highly suitable host crop increases herbivore pressure in intensified agricultural landscapes

“…Adult C. cinctus are relatively weak fliers, and generally oviposit in the nearest suitable host stem, but can move up to 800 m if suitable oviposition sites are not present at sites where adults eclose (Criddle, 1922). Oviposition preference can be influenced by a number of factors including plant developmental stage, stem diameter and plant volatiles (Ainslie, 1920;Holmes and Peterson, 1960;Buteler and Weaver, 2012).…”