Wheat Stem Sawfly Research Articles

Advancing Biological Control of the Wheat Stem Sawfly: New Strategies in a 100-yr Struggle to Manage a Costly Pest in the Northern Great Plains

For more than 100 yrs, the wheat stem sawfly (WSS) Cephus cinctus Norton (Hymenoptera: Cephidae), has been a destructive pest of cereal crops in the Northern Great Plains. WSS infestation levels >70% have been reported, and economic loss from crop damage caused by this insect can be as high as $80 million (USD) per year in the state of Montana alone. Contact insecticides are not effective against WSS because the larvae and pupae are protected inside the plant stem, and the development of solid-stem cultivars have not resulted in sufficient declines in WSS populations. Biological control offers the best hope for achieving economical and sustainable management of WSS. However, development and advancement of WSS biological control strategies has been limited in recent years. Presently, there are three main types of biologicals available for managing WSS: two native hymenopteran parasitoids, entomopathogenic nematodes, and entomopathogenic fungi. Here, we present the most current research regarding the use of these biologicals against WSS, and we discuss new strategies and research opportunities for improving their effectiveness for managing this persistent pest. It is unlikely that a single agent will produce the desired results, but by increasing pressure from all three sources, their combined impact may more reliably cause significant reductions in WSS infestations. Eradication of WSS, a native species, is not a realistic goal, but it is probable that WSS populations will decline more readily as biological control methods continue to advance.

A large-scale multiomics analysis of wheat stem solidness and the wheat stem sawfly feeding response, and syntenic associations in barley, Brachypodium, and rice

The wheat stem sawfly (WSS), Cephus cinctus Norton (Hymenoptera: Cephidae), is an important pest of wheat and other cereals, threatening the quality and quantity of grain production. WSS larvae feed and develop inside the stem where they are protected from the external environment; therefore, pest management strategies primarily rely on host plant resistance. A major locus on the long arm of wheat chromosome 3B underlies most of the variation in stem solidness; however, the impact of stem solidness on WSS feeding has not been completely characterized. Here, we used a multiomics approach to examine the response to WSS in both solid- and semi-solid-stemmed wheat varieties. The combined transcriptomic, proteomic, and metabolomic data revealed that two important molecular pathways, phenylpropanoid and phosphate pentose, are involved in plant defense against WSS. We also detected a general downregulation of several key defense transcripts, including those encoding secondary metabolites such as DIMBOA, tricetin, and lignin, which suggested that the WSS larva might interfere with plant defense. We comparatively analyzed the stem solidness genomic region known to be associated with WSS tolerance in wild emmer, durum, and bread wheats, and described syntenic regions in the close relatives barley, Brachypodium, and rice. Additionally, microRNAs identified from the same genomic region revealed potential regulatory pathways associated with the WSS response. We propose a model outlining the molecular responses of the WSS–wheat interactions. These findings provide insight into the link between stem solidness and WSS feeding at the molecular level.

Characterization of Resistance to Cephus cinctus (Hymenoptera: Cephidae) in Barley Germplasm.

Most barley cultivars have some degree of resistance to the wheat stem sawfly (WSS), Cephus cinctus Norton (Hymenoptera: Cephidae). Damage caused by WSS is currently observed in fields of barley grown in the Northern Great Plains, but the impact of WSS damage among cultivars due to genetic differences within the barley germplasm is not known. Specifically, little is known about the mechanisms underlying WSS resistance in barley. We characterized WSS resistance in a subset of the spring barley CAP (Coordinated Agricultural Project) germplasm panel containing 193 current and historically important breeding lines from six North American breeding programs. Panel lines were grown in WSS infested fields for two consecutive years. Lines were characterized for stem solidness, stem cutting, WSS infestation (antixenosis), larval mortality (antibiosis), and parasitism (indirect plant defense). Variation in resistance to WSS in barley was compared to observations made for solid-stemmed resistant and hollow-stemmed susceptible wheat lines. Results indicate that both antibiosis and antixenosis are involved in the resistance of barley to the WSS, but antibiosis seems to be more prevalent. Almost all of the barley lines had greater larval mortality than the hollow-stemmed wheat lines, and only a few barley lines had mortality as low as that observed in the solid-stemmed wheat line. Since barley lines lack solid stems, it is apparent that barley has a different form of antibiosis. Our results provide information for use of barley in rotation to control the WSS and may provide a basis for identification of new approaches for improving WSS resistance in wheat.

Cis-Jasmone treatments affect pests and beneficial insects of wheat (Triticum aestivum L.): the influence of doses and plant growth stages

cis-Jasmone (CJ) is a natural plant volatile derived from linolenic acid via the octadecanoid pathway, and acts as a semiochemical and plant defense elicitor. In the present study, the effects of three different CJ doses (25 g.ha−1; 50 g.ha−1; 100 g.ha−1), applied at two different wheat growth stages (flag leaf just visible and emergence of inflorescence completed), on wheat insect pests and beneficial insects were investigated using three different sampling methods (direct visual counting, sweep-netting, colored sticky traps) under semi-arid conditions during 2011–2013.Depending on the insect species, CJ dose-effects varied with study years, plant growth stages and/or sampling methods. Among the pest species, cereal aphids (apterous and alate) were the most prominently affected by CJ treatment, irrespective of the dose; fewer aphids were detected on the CJ-treated plants than on untreated control plants by direct visual counting, sweep net and yellow sticky trap samplings. CJ treatment also had deterrent effects on phytophagous thrips species and wheat stem sawflies (Hymenoptera: Cephidae), whereas CJ was an attractant for aphid parasitoids, coccinellid species and the wheat stem sawfly parasitoid Collyria coxator (Hymenoptera: Ichneumonidae). CJ treatment had no effect on syrphid species (Diptera: Syrphidae). There was no significant effect of CJ treatment on wheat yield; however, CJ-treated plants were taller than untreated control plants.Although the behavioral responses of the studied species to CJ treatment varied with the plant growth stage and treatment dose, and were not consistent across all sampling methods, our findings indicate CJ treatment may be used to reduce some insect pest populations and manipulate some natural enemy species under field conditions.

Combating WHEAT STEM SAWFLY in Colorado

In 2010, the wheat stem sawfly began causing problems for Colorado's winter wheat farmers. Back then, it was confined to the state's northeast corner, and the impact were small. Today, it's become a serious problem, with 54% of fields surveyed in eastern Colorado having the pest in 2017. What can producers and CCAs do to manage the sawfly in Colorado? Earn 1 CEU in Integrated Pest Management by reading this article and taking the quiz at www.certifiedcropadviser.org/education/classroom/classes/534.

Assembly and Annotation of Transcriptome Provided Evidence of miRNA Mobility between Wheat and Wheat Stem Sawfly.

Wheat Stem Sawfly (WSS), Cephus Cinctus Norton (Hymenoptera: Cephidae), is one of the most important pests, causing yield and economic losses in wheat and barley. The lack of information about molecular mechanisms of WSS for defeating plant’s resistance prevents application of effective pest control strategies therefore, it is essential to identify the genes and their regulators behind WSS infestations. Long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) are recognized with their regulatory functions on gene expression, tuning protein production by controlling transcriptional and post-transcriptional activities. A transcriptome-guided approach was followed in order to identify miRNAs, lncRNAs, and mRNA of WSS, and their interaction networks. A total of 1,893 were presented here as differentially expressed between larva and adult WSS insects. There were 11 miRNA families detected in WSS transcriptome. Together with the annotation of 1,251 novel mRNAs, the amount of genetic information available for WSS was expanded. The network between WSS miRNAs, lncRNAs, and mRNAs suggested miRNA-mediated regulatory roles of lncRNAs as competing endogenous RNAs. In the light of the previous evidence that small RNA molecules of a pathogen could suppress the immune response of host plant, we analyzed the putative interactions between larvae and wheat at the miRNA level. Overall, this study provides a profile of larva and adult WSS life stages in terms of coding and non-coding elements. These findings also emphasize the potential roles of wheat and larval miRNAs in wheat resistance to infestation and in the suppression of resistance which is critical for the development of effective pest control strategies.

Identification of Candidate Genes Responsible for Stem Pith Production Using Expression Analysis in Solid-Stemmed Wheat.

The wheat stem sawfly (WSS) is an economically important pest of wheat in the Northern Great Plains. The primary means of WSS control is resistance associated with the single quantitative trait locus (QTL) , which controls most stem solidness variation. The goal of this study was to identify stem solidness candidate genes via RNA-seq. This study made use of 28 single nucleotide polymorphism (SNP) makers derived from expressed sequence tags (ESTs) linked to contained within a 5.13 cM region. Allele specific expression of EST markers was examined in stem tissue for solid and hollow-stemmed pairs of two spring wheat near isogenic lines (NILs) differing for the QTL. Of the 28 ESTs, 13 were located within annotated genes and 10 had detectable stem expression. Annotated genes corresponding to four of the ESTs were differentially expressed between solid and hollow-stemmed NILs and represent possible stem solidness gene candidates. Further examination of the 5.13 cM region containing the 28 EST markers identified 260 annotated genes. Twenty of the 260 linked genes were up-regulated in hollow NIL stems, while only seven genes were up-regulated in solid NIL stems. An -methyltransferase within the region of interest was identified as a candidate based on differential expression between solid and hollow-stemmed NILs and putative function. Further study of these candidate genes may lead to the identification of the gene(s) controlling stem solidness and an increased ability to select for wheat stem solidness and manage WSS.

Characterization of resistance to the wheat stem sawfly in spring wheat landrace accessions from targeted geographic regions of the world

Plant landraces have long been recognized as potential gene pools for biotic and abiotic stress-related genes. This research used spring wheat landrace accessions to identify new sources of resistance to the wheat stem sawfly (WSS) (Cephus cinctus Norton), an important insect pest of wheat in the northern Great Plains of North America. Screening efforts targeted 1409 accessions from six geographical areas of the world where other species of grain sawflies are endemic or where a high frequency of accessions possesses the resistance characteristic of solid stems. Resistance was observed in approximately 14% of accessions. Half of the lines displayed both antixenosis and antibiosis types of resistance. Among the resistant accessions, 41% had solid or semi-solid stems. Molecular genetic screening for haplotypes at the solid stem QTL, Qss.msub.3BL, showed that 15% of lines shared the haplotype derived from ‘S-615’, the original donor of the solid stem trait to North American germplasm. Other haplotypes associated with solid stems were also observed. Haplotype diversity was greater in the center of origin of wheat. Evaluation of a representative set of resistant landrace accessions in replicated field trials at four locations over a three year period identified accessions with potential genes for reduced WSS infestation, increased WSS mortality, and increased indirect defense via parasitoids. Exploitation of distinct types of plant defense will expand the genetic diversity for WSS resistance currently present in elite breeding lines.

Registration of ‘Loma’ Hard Red Winter Wheat

‘Loma’ (Reg. No. CV‐1126, PI 680576) hard red winter wheat (Triticum aestivum L.) was developed and released by the Montana Agricultural Experiment Station in 2016. Loma was derived from the cross ‘Yellowstone’//MTS0112/MTS0125. It was developed using a modified bulk breeding method and selected as an F6:7 head row. Loma was tested under the experimental number MTS1224 in Montana yield trials from 2012 to 2016. Like the predominant cultivar Yellowstone, Loma is a high‐yielding, winter‐hardy wheat cultivar with medium to late maturity, medium to high grain protein concentration, and acceptable milling and baking quality characteristics. Loma was released for its excellent performance in winter wheat production environments of north‐central Montana, reduced plant height, and its semisolid stem, which provides some host plant resistance to wheat stem sawfly (Cephus cinctus Nort.).

Host Plants of the Wheat Stem Sawfly (Hymenoptera: Cephidae).

Wheat stem sawfly (Cephus cinctus Norton) is a pest of economic importance across much of the wheat (Triticum aestivum L.)-growing areas of the western Great Plains of North America as well as an ecologically important insect owing to its wide range of grass hosts. Little research has been published regarding the noncultivated native and invasive grasses attacked by this insect. Knowledge of the complete host range of C. cinctus can inform future research about potential new sources of genetic resistance, improve understanding of the biology and spread of natural enemies, and better define this insect's role in grassland and agricultural systems. The aim of this review is to compile a checklist of reported host plants of C. cinctus and present data from an extensive survey of noncultivated hosts used by C. cinctus.

High density mapping and haplotype analysis of the major stem-solidness locus SSt1 in durum and common wheat.

Breeding for solid-stemmed durum (Triticum turgidum L. var durum) and common wheat (Triticum aestivum L.) cultivars is one strategy to minimize yield losses caused by the wheat stem sawfly (Cephus cinctus Norton). Major stem-solidness QTL have been localized to the long arm of chromosome 3B in both wheat species, but it is unclear if these QTL span a common genetic interval. In this study, we have improved the resolution of the QTL on chromosome 3B in a durum (Kofa/W9262-260D3) and common wheat (Lillian/Vesper) mapping population. Coincident QTL (LOD = 94–127, R2 = 78–92%) were localized near the telomere of chromosome 3BL in both mapping populations, which we designate SSt1. We further examined the SSt1 interval by using available consensus maps for durum and common wheat and compared genetic to physical intervals by anchoring markers to the current version of the wild emmer wheat (WEW) reference sequence. These results suggest that the SSt1 interval spans a physical distance of 1.6 Mb in WEW (positions 833.4–835.0 Mb). In addition, minor QTL were identified on chromosomes 2A, 2D, 4A, and 5A that were found to synergistically enhance expression of SSt1 to increase stem-solidness. These results suggest that developing new wheat cultivars with improved stem-solidness is possible by combining SSt1 with favorable alleles at minor loci within both wheat species.

Phenotypic and Haplotype Diversity among Tetraploid and Hexaploid Wheat Accessions with Potentially Novel Insect Resistance Genes for Wheat Stem Sawfly.

Genetic diversity in breeding programs can be impaired by fixation of alleles derived from a limited number of founder lines. This is demonstrated with the use of a solid-stem trait derived from the Portuguese landrace 'S-615' over 70 yrs ago that is widely used to resist the wheat stem sawfly ( Norton, WSS) in North America. The objective of this study was to evaluate haplotype diversity underlying the quantitative trait locus (QTL) that controls the majority of the S-615 derived solid-stem genetic variation using single-nucleotide polymorphism (SNP) assays in a diverse set of 228 solid-stem tetraploid and hexaploid wheat accessions originating from areas of the world infested with various species of WSS. Haplotype analysis showed all WSS-resistant hexaploid wheat varieties in North America, except 'Conan', evaluated in this study contain a haplotype associated with the S-615 solid-stem allele. In total, 26 haplotypes were identified among the hexaploid and tetraploid accessions at . Prevalence of most haplotypes were skewed toward either the hexaploid or tetraploid wheat accessions. The haplotype found in the S-615- hexaploid wheat landrace was not found in the solid-stem tetraploid landrace accessions evaluated in this study. Haplotype analysis revealed several new haplotypes that have potential to contain novel alleles for solid-stems at , which may form the basis for introducing genetic diversity into breeding programs aimed at WSS resistance.

An Artificial Neural Network Model to Predict Wheat Stem Sawfly Cutting in Solid-Stemmed Wheat Cultivars

The wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), is a major pest of wheat (Triticum aestivum L.) in the northern Great Plains of North America. The use of solid-stemmed cultivars helps mitigate crop losses and can also affect the survivorship of C. cinctus. The efficacy of a plant’s resistance is based on its ability to develop pith in the culm of the stem, which is influenced greatly by interactions between the genotype and environment. Precipitation-related weather interacts with photoperiod to reduce pith expression in solid-stemmed wheat. A model that predicts pith expression could serve as a management tool to prevent losses by alerting producers if in-season precipitation patterns have caused less than ideal pith expression in a cultivar. Artificial Neural Network (ANN) models are used to make predictions for complex, non-linear systems with many co-related variables. Our objective was to improve upon past models that used regression analyses by deploying an ANN model to predict...

Host plant quantitative trait loci affect specific behavioral sequences in oviposition by a stem-mining insect.

Genetic diversity in quantitative loci associated with plant traits used by insects as cues for host selection can influence oviposition behavior and maternal choice. Host plant selection for oviposition is an important determinant of progeny performance and survival for phytophagous insects. Specific cues from the plant influence insect oviposition behavior; but, to date, no set of host plant quantitative trait loci (QTLs) have been shown to have an effect on behavioral sequences leading to oviposition. Three QTLs in wheat (Triticum aestivum L.) have been identified as influencing resistance to the wheat stem sawfly (WSS) (Cephus cinctus Norton). Wheat near-isogenic lines (NILs) for each of the three QTLs were used to test whether foraging WSS were able to discriminate variation in plant cues resulting from allelic changes. A QTL on chromosome 3B (Qss-msub-3BL) previously associated with stem solidness and larval antibiosis was shown to affect WSS oviposition behavior, host preference, and field infestation. Decreased preference for oviposition was also related to a QTL allele on chromosome 2D (Qwss.msub-2D). A QTL on chromosome 4A (Qwss.msub-4A.1) affected host plant attractiveness to foraging females, but did not change oviposition preference after females landed on the stem. These findings show that oviposition decisions regarding potential plant hosts require WSS females to discriminate signals from the plant associated with allelic variation at host plant quantitative loci. Allele types in a host plant QTL associated with differential survival of immature progeny can affect maternal choices for oviposition. The multidisciplinary approach used here may lead to the identification of plant genes with important community consequences, and may complement the use of antibiosis due to solid stems to control the wheat stem sawfly in agroecosystems.

MODIS Imagery Improves Pest Risk Assessment: A Case Study of Wheat Stem Sawfly (Cephus cinctus, Hymenoptera: Cephidae) in Colorado, USA.

Wheat stem sawfly (Cephus cinctus Norton, Hymenoptera: Cephidae) has long been a significant insect pest of spring, and more recently, winter wheat in the northern Great Plains. Wheat stem sawfly was first observed infesting winter wheat in Colorado in 2010 and, subsequently, has spread rapidly throughout wheat production regions of the state. Here, we used maximum entropy modeling (MaxEnt) to generate habitat suitability maps in order to predict the risk of crop damage as this species spreads throughout the winter wheat-growing regions of Colorado. We identified environmental variables that influence the current distribution of wheat stem sawfly in the state and evaluated whether remotely sensed variables improved model performance. We used presence localities of C. cinctus and climatic, topographic, soils, and normalized difference vegetation index and enhanced vegetation index data derived from Moderate Resolution Imaging Spectroradiometer (MODIS) imagery as environmental variables. All models had high performance in that they were successful in predicting suitable habitat for C. cinctus in its current distribution in eastern Colorado. The enhanced vegetation index for the month of April improved model performance and was identified as a top contributor to MaxEnt model. Soil clay percent at 0-5 cm, temperature seasonality, and precipitation seasonality were also associated with C. cinctus distribution in Colorado. The improved model performance resulting from integrating vegetation indices in our study demonstrates the ability of remote sensing technologies to enhance species distribution modeling. These risk maps generated can assist managers in planning control measures for current infestations and assess the future risk of C. cinctus establishment in currently uninfested regions.

Registration of ‘Lanning’ Hard Red Spring Wheat

‘Lanning’ hard red spring wheat (Reg. No. CV‐1120, PI 676978) (Triticum aestivum L.) was released by the Montana Agricultural Experiment Station due to its excellent yield potential in dryland areas of Montana and its superior end‐use quality. Lanning was derived from the cross ‘Glenn’/MT0747 by single seed descent beginning in the F2 generation. A single plant in the F4 generation was the source of experimental line MT1316, which subsequently was named Lanning. Lanning has grain yield equivalent to ‘Vida’, the most widely grown cultivar in Montana from 2010 to 2015. Lanning has higher grain protein and stronger gluten characteristics than Vida. Lanning is hollow stemmed, suggesting that it will be susceptible to damage caused by the wheat stem sawfly (Cephus cinctus Nort.). Lanning should be of interest to producers of hard red spring on dryland acreage throughout the wheat‐growing region of Montana.

Alleles at a quantitative trait locus for stem solidness in wheat affect temporal patterns of pith expression and level of resistance to the wheat stem sawfly

AbstractThe stem solidness trait in wheat has been the most effective mechanism for management of the wheat stem sawfly (WSS) for six decades. However, recent results have shown that in certain genotypes, the degree of stem solidness is not a useful indicator of WSS resistance. A morphological characterization of solidness expression indicated that in the genotype ‘Conan’, very solid pith undergoes rapid retraction during stem maturation, resulting in significantly less solidness at maturity. In other solid‐stemmed genotypes, including the standard WSS‐resistant cultivar ‘Choteau’, dense pith in the stem remains nearly unchanged throughout plant development. In cage trials, ‘Conan’ plants were less preferred for oviposition by the WSS when paired with ‘Choteau’ plants. Field bioassays using near‐isogenic lines differing for alleles at Qss.msub‐3BL showed that the Conan allele provides higher levels of early stem solidness and rapid pith retraction during stem maturation. These results suggest that the traditional approach for increasing WSS resistance by selecting for increasing stem solidness needs to be modified to consider temporal variations in pith expression associated with alleles at Qss.msub‐3BL.

AAC Cabri Durum Wheat

AAC Cabri durum wheat [Triticum turgidum L. subsp. durum (Desf.) Husn.] is adapted to the durum production area of the Canadian prairies. AAC Cabri has a solid stem that provides protection against the wheat stem sawfly (Cephus cinctus Norton). Averaged over four years, AAC Cabri yielded significantly more grain than Strongfield, AC Avonlea, and AC Navigator, but the protein concentration was significantly lower than the high protein concentration cultivars AC Avonlea and Strongfield. AAC Cabri is eligible for grades of Canada Western Amber Durum and has low grain cadmium concentration.

Effect of Wheat Cultivars and Blends on the Oviposition and Larval Mortality ofCephus cinctus(Hymenoptera: Cephidae) and Parasitism byBracon cephi(Hymenoptera: Braconidae)

The wheat stem sawfly (Cephus cinctus Norton) is a major historical pest of wheat in the northern Great Plains of North America. The insect spends most of its life as a larva protected inside grass stems so that its management has relied on strategies other than insecticides. We conducted a study in southern Alberta from 2006-2009 to assess the effects of wheat species, cultivar, seeding rate, and blending a resistant and a vulnerable cultivar, on oviposition, larval infestation, and cutting damage. The mortality caused by its primary parasitoid, Bracon cephi (Gahan), was also assessed to investigate the potential benefit of cultivar blends to enhance sawfly biological control. Sawfly laid fewer eggs on plants of the durum cultivar 'AC Avonlea' and on those of the solid-stemmed cultivar 'Lillian' compared to plants of the hollow-stemmed cultivar 'CDC Go.' Larval establishments (infestation) followed a similar pattern to that of oviposition. At these locations there was low cutting damage in most years and to a large extent this was due to mortality inflicted by the parasitoid Bracon cephi (40-60%). However, the remaining mortality was attributed to other factors and host, particularly the inclusion of the solid-stemmed cultivar. Direct and indirect factors likely affected the success of the parasitoid in the crop monocultures and blends, and these mechanisms require further research.

Sowing Density and Cultivar Effects on Pith Expression in Solid‐Stemmed Durum Wheat

The wheat stem sawfly (WSS) (Cephus cinctus; Hymenoptera: Cephidae) is a destructive insect pest of spring, winter (Triticum aestivum L.), and durum wheat (Triticum turgidum L. var. durum) in North America. Sawfly larvae hatch from eggs deposited inside the stem, and their subsequent feeding damages vascular tissue, reducing photosynthetic capacity and grain yields. Growing solid‐stemmed wheat cultivars that develop pith in the culm lumen is the most effective method to minimize yield losses. Recent work has focused on optimizing sowing densities to achieve maximum levels of pith expression and grain yields in common wheat; however, little research has been conducted on durum wheat. We investigated the influence of four sowing densities (150, 250, 350, 450 seeds m−2) on pith expression in two newly released solid‐stemmed durum cultivars, CDC Fortitude and AAC Raymore, and compared them to the solid‐stemmed common wheat cultivar, Lillian. CDC Fortitude and AAC Raymore displayed consistently high levels of pith expression across environments and sowing densities, in contrast to Lillian, which produced only slightly more pith than the hollow‐stemmed durum check cultivar, Strongfield. A yield drag often associated with high pith expression was not evident as CDC Fortitude and AAC Raymore produced grain yield similar to Strongfield. When averaged over cultivars, increasing sowing density had a positive effect on grain yield, but was negatively associated with stem solidness. Our findings suggest that, unlike with CWRS solid‐stemmed cultivars, altering sowing density is not required to achieve effective sawfly resistance with CDC Fortitude and AAC Raymore.