David K. Weaver

The endophytic fungus Alternaria oxytropis is vertically transmitted through silky crazyweed ( Oxytropis sericea Nutt.) and produces the neurotoxin swainsonine, yet its influence on host chemical signaling remains unclear. Here we characterize the floral and foliar volatile organic compound (VOC) profiles of endophyte-infected (E+) and endophyte-free (E-) O. sericea using dynamic headspace GC-MS on greenhouse- and field-grown plants – the first characterization of volatile profiles in this species. Endophyte infection had a negligible effect on VOC composition, explaining less than 1% of compositional variance in both greenhouse and field settings, with no compound differing consistently by infection status. Seven volatiles were reliably detected across both environments. The dominant axes of variation (PCA) instead reflected differences among individuals and between size-matched E+/E- plant across years. These accounted for most compositional variance (72.6% greenhouse, 64.9% field), and VOC profiles differed markedly between collection years, likely reflecting fine-scale environmental and physiological variation. Ancillary nectar assays and pollinator observations revealed no consistent differences between E + and E- plants, and seed set was unaffected regardless of endophyte status. Swainsonine in floral organs was roughly an order of magnitude lower than in leaves and near-trace in nectar, indicating that any localized chemical defense is likely decoupled from scent chemistry. Together, these findings position the Oxytropis-Alternaria association toward the commensal end of the symbiotic continuum: the fungus maintains vertical transmission while the host shows no detectable effect on volatile signaling, pollinator attraction, or reproductive output, despite the resources required to sustain fungal alkaloid biosynthesis. This system offers a tractable model for understanding how endophyte associations persist in the absence of measurable host benefit.

The wheat stem sawfly (WSS, Cephus cinctus Norton) is a major insect pest of wheat (Triticum aestivum L.) in North America. Few management tactics exist, and quantifying their efficacy is confounded by the difficulty in monitoring infestation at the field scale. Accurate estimates of WSS infestation are cost prohibitive as they rely on comprehensive stem dissection surveys due to the concealed life cycle of the pest. Consolidating the available management tactics into an effective strategy requires inexpensive, spatially explicit estimates of WSS infestation that are compatible with the large field sizes dryland wheat is often sown to. Therefore, we investigated using multitemporal satellite passive remote sensing (RS) to estimate various metrics of WSS infestation collected from field surveys at the subfield scale. To achieve this, we dissected 43,155 individual stems collected from 1158 unique locations across 9 production wheat fields in Montana, USA. The dissected stem samples from each location were then quantified using the following metrics: the proportion of total WSS-infested stems, proportion of stems with more than one node burrowed through (adequate WSS infestations), and proportion of WSS cut stems only. Cloud-free Sentinel 2 images were collected from Google Earth Engine for each field from across the growing season and sparse multiway partial least squares regression was used to produce a model for total WSS infestations, adequate WSS infestations, and WSS cut stems, for each sampled field. Upon comparing the performance of these models, we found that, on average, the metrics for total (R² = 0.57) and adequate WSS infestations (R² = 0.57) were more accurately estimated than WSS cut (R² = 0.34). The results of this study indicate that multitemporal RS can help estimate total and adequate WSS infestations, but more holistic methods of field level sensing should be explored, especially for estimating WSS cutting.

The wheat stem sawfly, Cephus cinctus Norton, is a major pest of cultivated wheat (Triticum aestivum L.) and other cereals in North America. The native congeneric parasitoids Bracon cephi (Gahan) and B. lissogaster Muesebeck are important biocontrol agents and play a crucial role in managing wheat stem sawfly outbreaks and damage. Smooth brome grass (Bromus inermis Leyss) has been found to be an effective wheat stem sawfly sink and parasitoid source when grown in areas neighboring wheat fields in Montana. To better understand the ecology of the system, we investigated both the wheat stem sawfly-induced volatile organic compounds produced by smooth brome and winter wheat, and the electrophysiological and behavioral response of B. cephi and B. lissogaster to the collected volatiles via coupled electroantennography and gas chromatography-flame ionization detection. Volatile concentration analysis indicated significantly increased production of (Z)-3-hexenyl acetate, 6-methyl-5-hepten-2-one, and (E)-2-hexenal in wheat stem sawfly-infested smooth brome, and elevated production of 6-methyl-5-hepten-2-one in infested smooth brome and winter wheat when compared to their uninfested counterparts. Both B. cephi and B. lissogaster exhibited significant electrophysiological and behavioral response to (Z)-3-hexenyl acetate, 6-methyl-5-hepten-2-one, and hexahydrofarnesyl acetone. Our results provide important evidence supporting habitat management recommendations that will enhance the effectiveness of biological control, contributing to more sustainable agricultural practices and the preservation of vital ecological functions.

Several metazoans live in extreme environments, but relatively little is known about the adaptations that these extremophiles have evolved to tolerate their conditions. The wetsalts tiger beetle, Cicindelidia hemorrhagica (LeConte) (Coleoptera: Cicindelidae), is found in the western USA, including the active geothermal springs in Yellowstone National Park (YNP). Here, we characterize behavioral, ecophysiological, and morphological traits of adult C. hemorrhagica living on hot springs in YNP compared to adults living in a non-hot spring environment in Idaho. Individuals in YNP behaviorally warmed and cooled themselves at surprisingly different frequencies than those in Idaho, with YNP individuals infrequently cooling themselves even though surface temperatures were greater because of geothermal activity and consequent bottom-up heating of individuals compared to the saline-flat habitat in Idaho. After a series of lethal thermal maxima and internal body temperature experiments, our results suggest that an explanation for the differential behavior is that the adult in YNP has evolved increased heat reflectance on the ventral portion of its abdomen. This increased heat reflectance seems to be caused by a physical feature as part of the exoskeleton’s ventral abdominal plate, which likely protects the beetle by serving as a heat-resistant shield. The extreme conditions in YNP seem to have selected C. hemorrhagica to be among the most thermophilic insects known.

Wheat stem sawfly (WSS) causes devastating yield loss in both common bread wheat (Triticum aestivum L.) and durum wheat (Triticum turgidum L. var durum) in the North American Great Plains. The early stem solidness phenotype confers solid stems early in plant development coinciding with the flight period of WSS and provides protection to plants during the critical oviposition period. With this phenotype, pith is lost as the plant develops, which may allow for enhanced biological control of surviving larvae by braconid parasitoids Bracon cephi (Gahan) and Bracon lissogaster Muesebeck, as well as having additional potential yield benefits from utilizing reabsorbed pith components. Here, we use an untargeted transcriptomics and metabolomics approach to explore the mechanisms related to the early stem solidness phenotype in three cultivars of spring wheat and two cultivars of durum wheat in addition to three near- isogenic pairs of spring wheat and two near- isogenic pairs of durum wheat. We identified effects of growth stage and allele on expression of metabolites and transcripts associated with stem solidness, development of cell walls and programmed cell death. A caffeic acid methylesterase and pectin methylesterase were upregulated in hollow stemmed Reeder and lines with the 3BLa allele, which likely influences lignin subunit proportions as well as the production of volatile semiochemicals that impact the behavior of adult WSS. TaVPE3cB, a gene associated with programmed cell death and thickening of cell walls, also had increased expression in hollow stemmed lines and is likely partially responsible for the hollow stemmed phenotype observed. Growth stage and allele also affected the expression of transcripts and metabolites involved in the phenylpropanoid pathway, carbohydrate and glycoside biosynthesis and lipid biosynthesis, implicating the involvement of these pathways in resistance and plant response to infestation by WSS.

Wheat stem sawfly (WSS), Cephus cinctus Norton (Hymenoptera: Cephidae), is a major pest of cereal crops throughout the Northern Great Plains of North America. Native parasitoids, Bracon cephi (Gahan) and B. lissogaster Muesebeck (Hymenoptera: Braconidae), play a key role in suppressing WSS populations and limiting associated damage. Smooth brome grass (Bromus inermis Leyss.) serves as a potential trap reservoir for WSS when grown in areas surrounding wheat (Triticum aestivum L.) fields in Montana. Its unique biology allows it to support high WSS infestation while promoting significant larval mortality throughout the growing season. Late-season WSS survivors can then serve as hosts for WSS parasitoids. Our study investigated smooth brome as a host refuge for WSS parasitoids. We measured WSS larval infestation and survival rate inside smooth brome grown within WSS-inclusion cages, finding a maximum infestation of 66.5% and an end-of-year WSS survival of 5.7%. In addition, we collected stems from sites in central and north-central Montana to measure the WSS infestation and parasitoid prevalence in wheat and adjacent smooth brome. WSS infestation was high in both Big Sandy (64.5% smooth brome, 65.7% adjacent wheat) and Moccasin, MT (50.6%, 38.6%). Year-end WSS larval mortality was 43.6% greater in smooth brome compared to adjacent wheat at both field sites, but both hosted similar numbers of WSS parasitoids. This research underscores the importance of smooth brome in providing a sustainable host refuge for WSS parasitoids and highlights its significant role in supporting the economics of wheat cultivation.

Wheat (Triticum aestivum L.) production in the Northern Great Plains of North America has been challenged by wheat stem sawfly (WSS), Cephus cinctus Norton, for a century. Damaging WSS populations have increased, highlighting the need for reliable surveys. Remote sensing (RS) can be used to correlate reflectance measurements with nuanced phenomena like cryptic insect infestations within plants, yet little has been done with WSS. To evaluate interactions between WSS-infested wheat and spectral reflectance, we grew wheat plants in a controlled environment, experimentally infested them with WSS and recorded weekly hyperspectral measurements (350–2500 nm) of the canopies from prior to the introduction of WSS to full senescence. To assess the relationships between WSS infestation and wheat reflectance, we employed sparse multiway partial least squares regression (N-PLS), which models multidimensional covariance structures inherent in multitemporal hyperspectral datasets. Multitemporal hyperspectral measurements of wheat canopies modeled with sparse N-PLS accurately estimated the proportion of WSS-infested stems (R² = 0.683, RMSE = 13.5%). The shortwave-infrared (1289–1380 nm) and near-infrared (942–979 nm) spectral regions were the most important in estimating infestation, likely due to internal feeding that decreases plant-water content. Measurements from all time points were important, suggesting aerial RS of WSS in the field should incorporate the visible through shortwave spectra collected from the beginning of WSS emergence at least weekly until the crop reaches senescence.

The wetsalts tiger beetle, Cicindelidia haemorrhagica (LeConte) (Coleoptera: Cicindelidae), is found in several active thermal hot spring areas in Yellowstone National Park (YNP) where substrate surface temperatures can exceed 50 °C. However, relationships between surface temperatures and the time adults spend on them remain poorly understood. Therefore, we characterized thermal profiles of Dragon Spring and Rabbit Creek, 2 thermally active research sites containing C. haemorrhagica in YNP, to quantify the time adults spend at different surface temperatures. We took 58 thermal video recordings of adults over 6 total days of observation ranging from 10 to 15 min for each adult. Thermal video analysis results indicated a positive relationship between the total time adult beetles spent on surface temperatures from Dragon Spring and Rabbit Creek as temperatures increased from 20 °C. Once surface temperatures exceeded 40 °C, the total time spent at those surface temperatures declined. Adults were recorded on substrates exceeding 50 °C at one of the 2 research locations. Rabbit Creek had substantially more instances of adults present with surface temperatures exceeding 40 °C, including one individual on a surface temperature of 61.5 °C. There were 3 instances of beetles spending more than 4 min at a particular surface temperature, all within the preferred range of 30–40 °C. Our thermal profile results and previous behavioral observations suggest that adults may be resistant to the heat produced from the thermal waters that influence the substrate temperatures but may not be subject to high surface temperatures as previously reported.

Introduction: Wheat stem sawfly (WSS), Cephus cinctus Norton, is a major pest of common bread wheat (Triticum aestivum L.) and other cultivated cereals in North America. Planting of cultivars with solid stems has been the primary management strategy to prevent yield loss due to WSS infestation, however expression of this phenotype can vary depending on environmental conditions and solid stems hinder biological control of WSS via braconid parasitoids Bracon cephi (Gahan) and Bracon lissogaster Muesebeck. In the hollow stems of oat (Avena sativa L.), WSS larvae experience 100% mortality before they reach late instars, but the mechanisms for this observed resistance have not been characterized. Objective: The objective of this study was to explore additional sources of resistance outside of the historic solid stem phenotype.Methods: Here, we use an untargeted metabolomics approach to examine the response of the metabolome of two cultivars of oat and four cultivars of spring wheat to infestation by WSS. Using liquid chromatography-mass spectrometry (LC-MS), differentially expressed metabolites were identified between oat and wheat which were associated with the phenylpropanoid pathway, phospholipid biosynthesis and signaling, the salicylic acid signaling pathway, indole-3-acetic acid (IAA) degradation, and biosynthesis of 1,4-benzoxazin-3-ones (Bxs). Several phospho- and galacto- lipids were found in higher abundance in oat, and with the exception of early stem solidness cultivar Conan, both species experienced a decrease in abundance once infested. In all wheat cultivars except Conan, an increase in abundance was observed for Bxs HMDBOA-glc and DIBOA-β-D-glucoside after infestation, indicating that this pathway is involved in wheat response to infestation in both solid and hollow stemmed cultivars. Differences between species in compounds involved in IAA biosynthesis, degradation and inactivation suggest that wheat may respond to infestation by inactivating IAA or altering the IAA pool in stem tissue.Conclusion: We propose that the species differences found here likely affect the survival of WSS larvae and may also be associated with differences in stem architecture at the molecular level. Our findings suggest pathways to focus on for future studies in elucidating plant response to WSS infestation.

The native parasitoids Bracon cephi (Gahan) and B. lissogaster Muesebeck (Hymenoptera: Braconidae) reduce populations of Cephus cinctus Norton (Hymenoptera: Cephidae), a native grassland species, and major wheat pest on the Northern Great Plains of North America. Non-host feeding adults of these braconids increase longevity, egg load, and egg volume when provisioned carbohydrate-rich diets. Nutrition from nectar can enhance the success of natural enemies in pest management programs. Cowpea, Vigna unguiculata (L.) Walpers, is a potential cover-crop that could add resilient features to the landscape and has extrafloral nectaries (EFN), easy-access nectar sources for beneficial insects. If more cowpea was grown on the Northern Great Plains, would B. cephi and B. lissogaster benefit from foraging on putatively beneficial EFN? We investigated cowpea inflorescence stalk extrafloral nectars (IS-EFN) and leaf stipel extrafloral nectars (LS-EFN) as potential food sources for these parasitoids. Females were caged on EFN sources on living cowpea plants to assess longevity. Egg load and volume were measured at 2, 5, and 10 days after placement. Bracon cephi survived 10 days on water, 38 days on IS-EFN; B. lissogaster 6 days on water, 28 days on IS-EFN. Bracon lissogaster maintained a constant egg load and volume across treatments while B. cephi produced 2.1-fold more eggs that were 1.6-fold larger on IS-EFN. Y-tube olfactometry indicated adult females were attracted to airstreams containing cowpea volatiles. These results demonstrate that non-native, warm-season cowpea benefits these native parasitoids and may improve conservation biocontrol of C. cinctus.