Untargeted metabolomics profiling of oat (Avena sativa L.) and wheat (Triticum aestivum L.) infested with wheat stem sawfly (Cephus cinctus Norton) reveals differences associated with plant defense and insect nutrition

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.

Cowpea extrafloral nectar has potential to provide ecosystem services lost in agricultural intensification and support native parasitoids that suppress the wheat stem sawfly

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.

Using Stable Isotopes to Determine Natal Origin and Feeding Habits of the Army Cutworm Moth, Euxoa auxiliaris (Lepidoptera: Noctuidae)

The army cutworm, Euxoa auxiliaris (Grote), is a migratory noctuid that is both an agricultural pest and an important late-season food source for grizzly bears, Ursus arctos horribilis (Linnaeus, Carnivora: Ursidae), within the Greater Yellowstone Ecosystem. Beyond the confirmation of the moths' seasonal, elevational migration in the mid-1900s, little else has been documented about their migratory patterns. To address this missing ecological component, we examined (1) migratory routes during their spring and fall migratory periods throughout their natal range, the Great Plains, and (2) natal origin at two of their summering ranges using stable hydrogen (δ2H) analyses of wings from samples collected within the areas of interest. Stable carbon (δ13C) and stable nitrogen (δ15N) analyses of wings were used to evaluate larval feeding habits of the migrants and agricultural intensity of natal origin sites, respectively. Results suggest that, rather than migrating exclusively east to west, army cutworm moths are also migrating north to south during their spring migration. Moths did not exhibit natal origin site fidelity when returning to the Great Plains. Migrants collected from the Absaroka Range had the highest probability of natal origin in Alberta, British Columbia, Saskatchewan, the most southern region of the Northwest Territories, and second highest probability of origin in Montana, Wyoming, and Idaho. Migrants collected in the Lewis Range had the highest probability of origin in the same provinces of Canada. Results suggest that migrants of the Absaroka Range fed exclusively on C3 plants as larvae and rarely fed in heavily fertilized agroecosystems.

Plant Volatiles and Oviposition Behavior in the Selection of Barley Cultivars by Wheat Stem Sawfly (Hymenoptera: Cephidae)

Wheat stem sawfly, [Cephus cinctus (Hymenoptera: Cephidae)], females display complex behaviors for host selection and oviposition. Susceptible hollow stem wheat (Triticum aestivum L.) cultivars release a greater amount of attractive compound, (Z)-3-hexenyl acetate and receive a greater number of eggs compared to resistant solid stem wheat cultivars. However, barley (Hordeum vulgare L.) is becoming a more common host for C. cinctus in Montana. Therefore, how do host selection and oviposition behaviors on barley cultivars compare to what happens when encountering wheat cultivars? To answer this question, we carried out greenhouse experiments using two barley cultivars: 'Hockett' and 'Craft'. Between these cultivars at Zadoks stages 34 and 49, we compared host selection decisions using a Y-tube olfactometer, compared oviposition behaviors on stems, and counted the number of eggs inside individual stems. In Y-tube bioassays, we found a greater number of C. cinctus females were attracted to the airstream passing over 'Hockett' than 'Craft' barley cultivars. Although the frequencies of oviposition behaviors were similar between these cultivars, the number of eggs was greater in 'Hockett'. Volatile profiles indicated that the amount of linalool was greater in the airstream from 'Craft' than in 'Hockett' at Zadoks 34 while the amount of (Z)-3-hexenyl acetate was greater in airstream from 'Hockett' at both Zadoks 34 and 49. These results suggest that volatiles of barley plants influenced host selection behavior of ovipositing C. cinctus females, while other discriminating behaviors do not differ between cultivars.

Impacts of Dryland Cropping Systems on Ground Beetle Communities (Coleoptera: Carabidae) in the Northern Great Plains

Ground beetles are natural predators of insect pests and small seeds in agroecosystems. In semiarid cropping systems of the Northern Great Plains, there is a lack of knowledge to how ground beetles are affected by diversified cover crop rotations. In a 2-yr study (2018 and 2019), our experiment was a restricted-randomization strip-plot design, comprising summer fallow, an early-season cover crop mixture (five species), and a mid-season cover crop mixture (seven species), with three cover crop termination methods (i.e., herbicide, grazing, and haying). Using pitfall traps, we sampled ground beetles in five 48-h intervals throughout the growing season (n = 135 per year) using growing degree day (GDD) accumulations to better understand changes to ground beetle communities. Data analysis included the use of linear mixed-effects models, perMANOVA, and non-metric multidimensional scaling ordinations. We did not observe differences among cover crop termination methods; however, activity density in the early-season cover crop mixture decreased and in summer fallow increased throughout the growing season, whereas the mid-season cover crop mixture peaked in the middle of the summer. Ground beetle richness and evenness showed a nonlinear tendency, peaking in the middle of the growing season, with marginal differences between cover crops or fallow after the termination events. Also, differences in ground beetle composition were greatest in the early- and mid-season cover crop mixtures earlier in the growing season. Our study supports the use of cover crop mixtures to enhance ground beetle communities, with potential implications for pest management in dryland cropping systems.

An Herbivore-Induced Plant Volatile From Saltcedar (Tamarix spp.) Is Repellent to Diorhabda carinulata (Coleoptera: Chrysomelidae)

The leaf beetle Diorhabda carinulata Desbrochers (Coleoptera: Chrysomelidae) was introduced into the United States in 1999 for classical biological control of the exotic woody invader saltcedar (Tamarix spp. L. [Caryophyllales: Tamaricaceae]). The recent southern expansion of the range of D. carinulata in the United States has precipitated conflict between proponents of biological control of Tamarix and those with concerns over habitat conservation for avian species. Several semiochemicals that mediate aggregations by this species have been reported, but no repellent compounds have been recorded thus far. We now report a repellent compound, 4-oxo-(E)-2-hexenal, induced by adult D. carinulata feeding on saltcedar foliage. Collection of headspace volatiles, gas chromatography mass spectrometry, and electroantennographic analyses identified 4-oxo-(E)-2-hexenal as an insect-induced compound that is antennally active. Behavioral and exposure assays were conducted to test for repellency and toxicity in adults and larvae. Headspace volatiles were also collected from adult males exposed to 4-oxo-(E)-2-hexenal to determine the impact exposure might have on the emission of the aggregation pheromone. 4-Oxo-(E)-2-hexenal elicited electrophysiological responses in adults of both sexes. Behavioral responses indicated repellency across multiple doses for reproductive D. carinulata adults but not in nonreproductive adults. Exposure assays indicated altered behaviors in first instar larvae and adults, but not in third instar larvae. Collection of headspace volatiles indicated that exposure to 4-oxo-(E)-2-hexenal did not alter emission of the D. carinulata aggregation pheromone by adult males. The continued development and field deployment of this repellent compound may provide a new tool for the management of D. carinulata.

Multiple decrement life tables of Cephus cinctus Norton (Hymenoptera: Cephidae) across a set of barley cultivars: The importance of plant defense versus cannibalism

Accurately estimating cause-specific mortality for immature insect herbivores is usually difficult. The insects are exposed to abiotic and biotic mortality factors, causing cadavers to simply disappear before cause of mortality can be recorded. Also, insect herbivores are often highly mobile on hosts, making it difficult to follow patterns for individuals through time. In contrast, the wheat stem sawfly, Cephus cinctus Norton, spends its entire egg, larval, and pupal period inside a host stem. Therefore, with periodic sampling stage-specific causes of mortality can be ascertained. Consequently, we examined C. cinctus mortality in eight barley, Hordeum vulgare L., cultivars in two locations in Montana from 2016 to 2018 by collecting stem samples from stem elongation to crop maturity at weekly intervals, and collecting overwintered barley stubs the following spring and summer from the same plots. If larvae were present, we examined larval status—dead or alive—and categorized dead individuals into one of 5 mortality categories: plant defense, cannibalism, parasitism, pathogens, and unknown factors. We used multiple decrement life tables to estimate cause-specific mortality and irreplaceable mortality (the proportion of mortality from a given cause that cannot be replaced by other causes of mortality). Plant defense (antibiosis) caused 85.7 ± 3.6%, cannibalism (governed by antixenosis) caused 70.1 ± 7.6%, parasitism caused 13.8 ± 5.9%, unknown factors caused 38.5 ± 7.6%, and pathogens caused 14.7 ± 8.5% mortality in the presence of all causes of mortality. Similarly, irreplaceable mortality due to plant defense was 22.3 ± 6.4%, cannibalism was 29.1± 4.2%, unknown factors was 6.2 ± 1.8%, pathogens was 0.9 ± 0.5%, and parasitism was 1. 5 ± 0. 6%. Antibiosis traits primarily killed newly emerged larvae, while other traits supported more favorable oviposition decisions by females, increasing mortality by obligate cannibalism. Our results suggest that breeding barley for resistance to C. cinctus targeting both categories of traits (antibiosis and antixenosis) is a highly valuable tactic for management of this important pest.

Effect of Precipitation and Temperature on Larval Survival of Cephus cinctus (Hymenoptera: Cephidae) in Barley Cultivars

Host plant traits strongly affect survivorship of insect herbivores, and host suitability is especially important for the wheat stem sawfly, Cephus cinctus Norton, which spends its entire egg, larval, and pupal periods in a single stem. Measuring larval survival inside stems from egg hatch through diapause-mediated dormancy is a potential measure of population size for the next year but is also useful in assessing effects of growing season precipitation and temperature. Larval growth is synchronized with host plant growth, and the larva cannot switch hosts. Thus, incorporating plant physiological time, as growing degree days (GDD), may yield a better prediction of larval survival. Therefore, we assessed wheat stem sawfly survival from early larval growth to the beginning of autumnal diapause in barley cultivars selected from across feed, forage, and two- or six-row malt groups. Field experiments were conducted in Gallatin and Chouteau counties, Montana, in 2016 and 2017. We used Kaplan-Meier estimation to assess larval survival among cultivars. We found that the survival of pre-diapause larvae was greatest in 'Hockett' (36.5%) and lowest in 'Celebration' (15.4%). Precipitation and temperature during the growing season affected temporal patterns for larval survival across study sites. Adjusting survivorship curves using site-specific GDD accumulation allowed cultivar-specific survivorship to be estimated more precisely for each site, despite differing environmental influences. Our findings suggest that measuring wheat stem sawfly survival across barley cultivars and standardizing by site-specific GDDs may provide better recommendations on barley cultivars that impede wheat stem sawfly population growth and reduce economic losses.

Antixenosis, Antibiosis, and Potential Yield Compensatory Response in Barley Cultivars Exposed to Wheat Stem Sawfly (Hymenoptera: Cephidae) Under Field Conditions

Wheat stem sawfly, Cephus cinctus Norton, is an economically serious pest of cereals grown in North America. Barley cultivars were previously planted as resistant crops in rotations to manage C. cinctus, but due to increasing levels of injury to this crop, this is no longer a valid management tactic in Montana. Therefore, we aimed to understand antixenosis (behavioral preference), antibiosis (mortality), and potential yield compensation (increased productivity in response to stem injuries) in barley exposed to C. cinctus. We examined these traits in eight barley cultivars. Antixenosis was assessed by counting number of eggs per stem and antibiosis was assessed by counting infested stems, dead larvae, and stems cut by mature larvae. Potential yield compensation was evaluated by comparing grain yield from three categories of stem infestation: 1) uninfested, 2) infested with dead larva, and 3) infested cut by mature larva at crop maturity. We found the greatest number of eggs per infested stem (1.80 ± 0.04), the highest proportion of infested stems (0.63 ± 0.01), and the highest proportion of cut stems (0.33 ± 0.01) in 'Hockett'. Seven out of eight cultivars had greater grain weight for infested stems than for uninfested stems. These cultivars may have compensatory responses to larval feeding injury. Overall, these barley cultivars contain varying levels of antixenosis, antibiosis, and differing levels of yield compensation. Our results provide foundational knowledge on barley traits that will provide a framework to further develop C. cinctus resistant or tolerant barley cultivars.

Establishing Diorhabda carinulata: Impact of Release Disturbances on Pheromone Emission and Influence of Pheromone Lures on Establishment

Before weed biocontrol insects are transported and released in a new area, they are commonly collected into small paper containers, chilled, and kept under dark conditions. This process can be termed a pre-release protocol. The influence of a pre-release protocol on establishment success of a gregarious biological control agent was assessed using the northern tamarisk beetle, Diorhabda carinulata (Desbrochers), and its exotic, invasive host plant saltcedar (Tamarix spp.). Pre-release protocol impacts on aggregation pheromone production by D. carinulata were characterized under controlled conditions. Additional experiments were undertaken to determine if deployment of aggregation pheromone lures might enhance the agent's persistence at release sites. Adults that experienced the pre-release protocol produced less aggregation pheromone compared to undisturbed adults. Olfactometer bioassays indicated that a cohort of adults subjected to the pre-release protocol were less attractive to other adults than a control cohort. Efficacy of aggregation pheromone-based lures to retain adults at release sites was evaluated by comparing capture numbers of adult beetles at paired treatment and control release sites, 10-14 days after the release of 300, 500, or 1000 individuals. A greater number of adult D. carinulata were captured where the pheromone lures had been deployed compared to control release sites. Application of aggregation pheromone when a new release of D. carinulata is planned should allow biological control practitioners to increase retention of beetles at a release site.

Field demonstration of a semiochemical treatment that enhances Diorhabda carinulata biological control of Tamarix spp

The northern tamarisk beetle Diorhabda carinulata (Desbrochers) was approved for release in the United States for classical biological control of a complex of invasive saltcedar species and their hybrids (Tamarix spp.). An aggregation pheromone used by D. carinulata to locate conspecifics is fundamental to colonization and reproductive success. A specialized matrix formulated for controlled release of this aggregation pheromone was developed as a lure to manipulate adult densities in the field. One application of the lure at onset of adult emergence for each generation provided long term attraction and retention of D. carinulata adults on treated Tamarix spp. plants. Treated plants exhibited greater levels of defoliation, dieback and canopy reduction. Application of a single, well-timed aggregation pheromone treatment per generation increased the efficacy of this classical weed biological control agent.

Genome-resolved insights into a novel Spiroplasma symbiont of the Wheat Stem Sawfly (Cephus cinctus)

Arthropods often have obligate relationships with symbiotic microbes, and recent investigations have demonstrated that such host-microbe relationships could be exploited to suppress natural populations of vector carrying mosquitos. Strategies that target the interplay between agricultural pests and their symbionts could decrease the burden caused by agricultural pests; however, the lack of comprehensive genomic insights into naturally occurring microbial symbionts presents a significant bottleneck. Here we employed amplicon surveys, genome-resolved metagenomics, and scanning electron microscopy to investigate symbionts of the wheat stem sawfly (Cephus cinctus), a major pest that causes an estimated $350 million dollars or more in wheat yield losses in the northwestern United States annually. Through 16S rRNA gene sequencing of two major haplotypes and life stages of wheat stem sawfly, we show a novel Spiroplasma species is ever-present and predominant, with phylogenomic analyses placing it as a member of the ixodetis clade of mollicutes. Using state-of-the-art metagenomic assembly and binning strategies we were able to reconstruct a 714 Kb, 72.7%-complete Spiroplasma genome, which represents just the second draft genome from the ixodetis clade of mollicutes. Functional annotation of the Spiroplasma genome indicated carbohydrate-metabolism involved PTS-mediated import of glucose and fructose followed by glycolysis to lactate, acetate, and propionoate. The bacterium also encoded biosynthetic pathways for essential vitamins B2, B3, and B9. We identified putative Spiroplasma virulence genes: cardiolipin and chitinase. These results identify a previously undescribed symbiosis between wheat stem sawfly and a novel Spiroplasma sp., availing insight into their molecular relationship, and may yield new opportunities for microbially-mediated pest control strategies.

Dryland Organic Farming Partially Offsets Negative Effects of Highly Simplified Agricultural Landscapes on Forbs, Bees, and Bee-Flower Networks

Industrialized farming practices result in simplified agricultural landscapes, reduced biodiversity, and degraded species-interaction networks. Thus far, most research assessing the combined effects of farming systems and landscape complexity on beneficial insects has been conducted in relatively diversified and mesic systems and may not represent the large-scale, monoculture-based dryland agriculture that dominates many regions worldwide. Specifically, the effects of farming systems on forbs, bees, and their interactions are poorly understood in highly simplified dryland landscapes such as those in the Northern Great Plains, United States, an area globally important for conventional and organic small grain, pulse, forage, and oilseed production. During a 3-yr (2013-2015) study, we assessed 1) the effects of dryland no-till conventional and tilled organic farming on forbs, bees, and bee-flower networks and 2) the relationship between natural habitat and bee abundance. Flower density and richness were greater in tilled organic fields than in no-till conventional fields, and forb community composition differed between farming systems. We observed high bee diversity (109 taxa) in this highly simplified landscape, and bee abundance, richness, and community composition were similar between systems. Compared with tilled organic fields, bee-flower interactions in no-till conventional fields were poorly connected, suggesting these systems maintain relatively impoverished plant-pollinator networks. Natural habitat (11% of the landscape) did not affect small-bodied bee abundance in either farming system but positively affected large-bodied bees within 2,000 m of crop-field centers. In highly simplified agricultural landscapes, dryland organic farming and no-till conventional farming together support relatively high bee diversity, presumably because dryland organic farming enhances floral resources and bee-flower networks, and no-till management in conventional farming provides undisturbed ground-nesting habitats for wild bees (Hymenoptera: Apoidea).

Analysis of recombinant inbred line populations derived from wheat landraces to identify new genes for wheat stem sawfly resistance

Wheat landrace accessions were chosen from areas of the world with historical European wheat stem sawfly (Cephus pygmaeus L.) selection pressure to develop six recombinant inbred line (RIL) populations. Molecular maps were constructed, and resistance due to antibiosis and antixenosis was assessed at sites in Montana naturally infested by Cephus cinctus Norton, the wheat stem sawfly (WSS). Novel QTLs were identified along with QTL previously identified in elite germplasm. A newly identified QTL on chromosome 1B provided a new source for pith-filled solid stems. An allele for resistance on chromosome 4A unrelated to solid stems was identified in four of the six RIL populations. A landrace from Turkey, PI 166471, contained alleles at three QTLs causing high levels of larval mortality. None of the QTLs were related to stem solidness, but their combined effect provided resistance similar to that observed in a solid-stemmed check cultivar. These results show the utility of genetic populations derived from geographically targeted landrace accessions to identify new alleles for insect resistance. New PCR-based molecular markers were developed for introgression of novel alleles for WSS resistance into elite lines. Comparison of results with previous analysis of elite cultivars addresses changes in allele frequencies during the wheat breeding process.

Effect of insecticide formulation and adjuvant combination on agricultural spray drift

Loss of crop protection products when agricultural spray applications drift has economic and ecological consequences. Modification of the spray solution through tank additives and product formulation is an important drift reduction strategy that could mitigate these effects, but has been studied less than most other strategies. Therefore, an experimental field study was conducted to evaluate spray drift resulting from agricultural ground applications of an insecticide formulated as a suspension concentrate (SC) and as a wettable powder (WP), with and without two adjuvants. Droplet sizes were also measured in a wind tunnel to determine if indirect methods could be substituted for field experimentation to quantify spray drift from these technologies. Results suggest that spray drift was reduced by 37% when comparing the SC to the WP formulation. As much as 63% drift reduction was achieved by incorporating certain spray adjuvants, but this depended on the formulation/adjuvant combination. The wind tunnel data for droplet spectra showed strong agreement with field deposition trends, suggesting that droplet statistics could be used to estimate drift reduction of spray solutions. These findings can be used to develop a classification scheme for formulated products and tank additives based on their potential for reducing spray drift.

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

BACKGROUND

Cephus cinctus infestation causes $350 million in annual losses in the Northern Great Plains. We compared infestation and parasitism of C. cinctus in spring (including Kamut; Triticum turgidum ssp. turanicum) and winter wheat cultivars grown in organic and conventional fields in Montana, USA. In the greenhouse, we compared C. cinctus preference and survival in Kamut, Gunnison, and Reeder spring wheat cultivars.

RESULTS

Stems cut by C. cinctus varied by farming system and the seasonality of the wheat crop. No stems of Kamut in organic fields were cut by C. cinctus, but 1.5% [±0.35% standard error (SE)] of stems in conventional spring wheat, 5% (±0.70% SE) of stems in organic winter wheat, and 20% (±0.93% SE) of stems in conventional winter wheat fields were cut by C. cinctus. More larvae of C. cinctus were parasitized in organic (27 ± 0.03% SE) compared with conventional (5 ± 0.01% SE) winter wheat fields. Cephus cinctus oviposition, survival, and the number of stems cut were lowest in Kamut compared with Gunnison and Reeder.

CONCLUSION

Cephus cinctus infestation was more common in winter wheat than in spring wheat. Organic fields with fewer cut stems also supported more parasitoids. Kamut is a genetic resource for developing C. cinctus-resistant cultivars. © 2018 Society of Chemical Industry.

Genome Sequence of the Wheat Stem Sawfly, Cephus cinctus, Representing an Early-Branching Lineage of the Hymenoptera, Illuminates Evolution of Hymenopteran Chemoreceptors

The wheat stem sawfly, Cephus cinctus, is a major pest of wheat and key ecological player in the grasslands of western North America. It also represents the distinctive Cephoidea superfamily of sawflies (Symphyta) that appeared early during the hymenopteran radiation, but after three early-branching eusymphytan superfamilies that form the base of the order Hymenoptera. We present a high-quality draft genome assembly of 162 Mb in 1,976 scaffolds with a scaffold N50 of 622 kb. Automated gene annotation identified 11,210 protein-coding gene models and 1,307 noncoding RNA models. Thirteen percent of the assembly consists of ∼58,000 transposable elements partitioned equally between Class-I and Class-II elements. Orthology analysis reveals that 86% of Cephus proteins have identifiable orthologs in other insects. Phylogenomic analysis of conserved subsets of these proteins supports the placement of the Cephoidea between the Eusymphyta and the parasitic woodwasp superfamily Orussoidea. Manual annotation and phylogenetic analysis of families of odorant, gustatory, and ionotropic receptors, plus odorant-binding proteins, shows that Cephus has representatives for most conserved and expanded gene lineages in the Apocrita (wasps, ants, and bees). Cephus has also maintained several insect gene lineages that have been lost from the Apocrita, most prominently the carbon dioxide receptor subfamily. Furthermore, Cephus encodes a few small lineage-specific chemoreceptor gene family expansions that might be involved in adaptations to new grasses including wheat. These comparative analyses identify gene family members likely to have been present in the hymenopteran ancestor and provide a new perspective on the evolution of the chemosensory gene repertoire.

Correction to: 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 original version of this article contained a mistake. The word "RefSeq v.1" was incorrectly inserted on page 7. The correct sentence should be: To identify the differentially regulated transcripts, clean RNA-Seq reads were mapped onto the T. aestivum Chinese Spring chromosome 3B pseudomolecule.

Semiochemicals to enhance herbivory by Diorhabda carinulata aggregations in saltcedar (Tamarix spp.) infestations

BACKGROUND

Semiochemicals for monitoring, attracting or repelling pest and beneficial organisms are increasingly deployed in agricultural and forest systems for pest management. However, the use of aggregation pheromones and host-plant attractants for the express purpose of increasing the efficacy of classical biological control agents of weeds has not been widely reported. Therefore, we conducted field-based assays to determine if a specialized wax-based matrix impregnated with an aggregation pheromone of the northern tamarisk beetle Diorhabda carinulata (Desbrochers) or host-plant volatiles could increase the efficacy of D. carinulata.

RESULTS

The aggregation pheromone and host-plant volatiles were formulated for field application using a wax-based matrix. Reported release rates suggest that this matrix is a viable formulation for enhancing D. carinulata aggregations under field conditions. Pheromone-treated saltcedar plants (Tamarix spp.) not only had higher densities of adult and larval D. carinulata, but also sustained greater levels of foliar damage than control plants. Increased damage from the focused feeding of D. carinulata caused an increase in foliar dieback and decrease in live canopy volume of semiochemical-treated plants.

CONCLUSION

Field deployment of these semiochemical formulations could be useful in directing populations of D. carinulata for increased impact on Tamarix spp. © 2018 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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.

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.

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.

Phylogeography of the Wheat Stem Sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae): Implications for Pest Management

The wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), is a key pest of wheat in the northern Great Plains of North America, and damage resulting from this species has recently expanded southward. Current pest management practices are inadequate and uncertainty regarding geographic origin, as well as limited data on population structure and dynamics across North America impede progress towards more informed management. We examined the genetic divergence between samples collected in North America and northeastern Asia, the assumed native range of C. cinctus using two mitochondrial regions (COI and 16S). Subsequently, we characterized the structure of genetic diversity in the main wheat producing areas in North America using a combination of mtDNA marker and microsatellites in samples collected both in wheat fields and in grasses in wildlands. The strong genetic divergence observed between North American samples and Asian congeners, in particular the synonimized C. hyalinatus, did not support the hypothesis of a recent American colonization by C. cinctus. Furthermore, the relatively high genetic diversity both with mtDNA and microsatellite markers offered additional evidence in favor of the native American origin of this pest. The genetic diversity of North American populations is structured into three genetic clusters and these are highly correlated with geography. Regarding the recent southern outbreaks in North America, the results tend to exclude the hypothesis of recent movement of damaging wheat stem sawfly populations from the northern area. The shift in host plant use by local populations appears to be the most likely scenario. Finally, the significance of these findings is discussed in the context of pest management.

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

KEY MESSAGE

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.

A Multiple Decrement Life Table Reveals That Host Plant Resistance and Parasitism Are Major Causes of Mortality for the Wheat Stem Sawfly

This study investigated the dynamics of parasitism, host plant resistance, pathogens, and predation on the demography of wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), developing in susceptible (hollow stem) and resistant (solid stem) wheat hosts. This study is also the first to investigate the prevalence and impact of cannibalism on wheat stem sawfly mortality. Wheat stem sawflies were sampled in two commercial wheat fields over 4 yr from the egg stage through adult emergence, and multiple decrement life tables were constructed and analyzed. Cannibalism, host plant resistance, or unknown factors were the most prevalent factors causing egg mortality. Summer mortality of prediapause larvae ranged from 28 to 84%, mainly due to parasitism by Bracon cephi (Gahan) and Bracon lissogaster Muesebeck, cannibalism, and host plant resistance. Winter mortality ranged from 6 to 54% of the overwintering larvae, mainly due to unknown factors or pathogens. Cannibalism is a major cause of irreplaceable mortality because it is absolute, with only a single survivor in every multiple infested stem. Subsequent to obligate cannibalism, mortality of feeding larvae due to host plant resistance was lower in hollow stem wheat than in solid stem wheat. Mortality from host plant resistance was largely irreplaceable. Irreplaceable mortality due to parasitoids was greater in hollow stem wheat than in solid stem wheat. Host plant resistance due to stem solidness and parasitism in hollow stems cause substantial mortality in populations of actively feeding larvae responsible for all crop losses. Therefore, enhancing these mortality factors is vital to effective integrated pest management of wheat stem sawfly.

Interacting agricultural pests and their effect on crop yield: application of a Bayesian decision theory approach to the joint management of Bromus tectorum and Cephus cinctus

Worldwide, the landscape homogeneity of extensive monocultures that characterizes conventional agriculture has resulted in the development of specialized and interacting multitrophic pest complexes. While integrated pest management emphasizes the need to consider the ecological context where multiple species coexist, management recommendations are often based on single-species tactics. This approach may not provide satisfactory solutions when confronted with the complex interactions occurring between organisms at the same or different trophic levels. Replacement of the single-species management model with more sophisticated, multi-species programs requires an understanding of the direct and indirect interactions occurring between the crop and all categories of pests. We evaluated a modeling framework to make multi-pest management decisions taking into account direct and indirect interactions among species belonging to different trophic levels. We adopted a Bayesian decision theory approach in combination with path analysis to evaluate interactions between Bromus tectorum (downy brome, cheatgrass) and Cephus cinctus (wheat stem sawfly) in wheat (Triticum aestivum) systems. We assessed their joint responses to weed management tactics, seeding rates, and cultivar tolerance to insect stem boring or competition. Our results indicated that C. cinctus oviposition behavior varied as a function of B. tectorum pressure. Crop responses were more readily explained by the joint effects of management tactics on both categories of pests and their interactions than just by the direct impact of any particular management scheme on yield. In accordance, a C. cinctus tolerant variety should be planted at a low seeding rate under high insect pressure. However as B. tectorum levels increase, the C. cinctus tolerant variety should be replaced by a competitive and drought tolerant cultivar at high seeding rates despite C. cinctus infestation. This study exemplifies the necessity of accounting for direct and indirect biological interactions occurring within agroecosystems and propagating this information from the statistical analysis stage to the management stage.

Odorant receptors of a primitive hymenopteran pest, the wheat stem sawfly

The wheat stem sawfly, Cephus cinctus, is an herbivorous hymenopteran that feeds exclusively on members of the Graminae family. Synanthropically, it has become one of the most important insect pests of wheat grown in the northern Great Plains region of the USA and Canada. Insecticides are generally ineffective because of the wheat stem sawfly's extended adult flight period and its inaccessible larval stage, during which it feeds within the wheat stems, making it virtually intractable to most pest management strategies. While research towards integrated pest management strategies based on insect olfaction has proved promising, nothing is known about the molecular basis of olfaction in this important pest species. In this study we identified 28 unique odorant receptor (Or) transcripts from an antennal transcriptome. A phylogenetic analysis with the predicted Ors from the honey bee and jewel wasp genomes revealed at least four clades conserved amongst all three Hymenoptera species. Antennal expression levels were analysed using quantitative real-time PCR, and one male-biased and five female-biased Ors were identified. This study provides the basis for future functional analyses to identify behaviourally active odours that can be used to help develop olfactory-mediated pest management tools.

Environmental fate model for ultra-low-volume insecticide applications used for adult mosquito management

One of the more effective ways of managing high densities of adult mosquitoes that vector human and animal pathogens is ultra-low-volume (ULV) aerosol applications of insecticides. The U.S. Environmental Protection Agency uses models that are not validated for ULV insecticide applications and exposure assumptions to perform their human and ecological risk assessments. Currently, there is no validated model that can accurately predict deposition of insecticides applied using ULV technology for adult mosquito management. In addition, little is known about the deposition and drift of small droplets like those used under conditions encountered during ULV applications. The objective of this study was to perform field studies to measure environmental concentrations of insecticides and to develop a validated model to predict the deposition of ULV insecticides. The final regression model was selected by minimizing the Bayesian Information Criterion and its prediction performance was evaluated using k-fold cross validation. Density of the formulation and the density and CMD interaction coefficients were the largest in the model. The results showed that as density of the formulation decreases, deposition increases. The interaction of density and CMD showed that higher density formulations and larger droplets resulted in greater deposition. These results are supported by the aerosol physics literature. A k-fold cross validation demonstrated that the mean square error of the selected regression model is not biased, and the mean square error and mean square prediction error indicated good predictive ability.

Cereal crop volatile organic compound induction after mechanical injury, beetle herbivory (Oulema spp.), or fungal infection (Fusarium spp.)

Herbivory, mechanical injury or pathogen infestation to vegetative tissues can induce volatile organic compounds (VOCs) production, which can provide defensive functions to injured and uninjured plants. In our studies with 'McNeal' wheat, 'Otana' oat, and 'Harrington' barley, plants that were mechanically injured, attacked by either of two Oulema spp. (melanopus or cyanella) beetles, or infected by one of the three Fusarium spp. (graminearum, avenaceum, or culmorum), had significant VOC induction compared to undamaged plants. Mechanical injury to the main stem or one leaf caused the induction of one green leaf volatile (GLV) - (Z)-3-hexenol, and three terpenes (β-linalool, β-caryophyllene, and α-pinene) with all three grasses; wheat and barley also showed β-linalool oxide induction. The blend of induced VOCs after Fusarium spp. infestation or Oulema spp. herbivory was dominated by GLVs ((Z)-3-hexenal, (E)-2-hexenal, (E)-2-hexenol, (Z)-3-hexenyl acetate, and 1-hexenyl acetate) and β-linalool and β-caryophyllene; beetle herbivory also induced (E)-β-farnesene. Different ratios of individual VOCs were induced between the two Oulema spp. for each cereal grass and different ratios across the three cereals for each beetle species. Also, different ratios of individual VOCs were induced between the three Fusarium spp. for each cereal grass and different ratios across the three cereals for each fungal pathogen species. Our results are preliminary since we could not simultaneously measure VOC induction from controls with each of the ten different injury treatments for each of the three cereals. However, the comparison of mechanical injury, insect herbivory, and fungal infection has not been previously examined with VOC responses from three different plant species within the same family. Also, our work suggests large qualitative and quantitative overlap of VOC induction from plants of all three cereals having beetle herbivory injury when compared to infection injury from necrotrophic fungal pathogens.

Novel use of nanostructured alumina as an insecticide

BACKGROUND

The worldwide need to produce an inexpensive and abundant food supply for a growing population is a great challenge that is further complicated by concerns about risks to environmental stability and human health triggered by the use of pesticides. The result is the ongoing development of alternative pest control strategies, and new, lower-risk insecticidal molecules. Among the recent technological advances in agricultural science, nanotechnology shows considerable promise, although its development for use in crop protection is in its initial stages.

RESULTS

This study reports for the first time the insecticidal effect of nanostructured alumina. Two species were used as model organisms, Sitophilus oryzae L. and Rhyzopertha dominica (F.), which are major insect pests in stored food supplies throughout the world. Both species experienced significant mortality after 3 days of continuous exposure to treated wheat. Nine days after treatment, the median lethal doses (LD(50)) observed ranged from 127 to 235 mg kg(-1).

CONCLUSION

Comparison of these results with recommended rates for commercial insecticidal dusts suggests that inorganic nanostructured alumina may provide a cheap and reliable alternative for control of insect pests. This study expands the frontiers for nanoparticle-based technologies in pest management. Further research is needed to identify its mode of action and its non-target toxicity, and to determine the potential of other nanostructured materials as pest control options for insects.

Photosynthesis and yield reductions from wheat stem sawfly (Hymenoptera: Cephidae): interactions with wheat solidness, water stress, and phosphorus deficiency

The impact of herbivory on plants is variable and influenced by several factors. The current study examined causes of variation in the impact of larval stem mining by the wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), on spring wheat, Triticum aestivum L. We performed greenhouse experiments over 2 yr to (1) study whether biotic (hollow versus solid stemmed host wheat) and abiotic (water, phosphorus stress) factors interact with C. cinctus stem mining to influence degree of mined stem physiological (photosynthesis) and yield (grain weight) reductions; and (2) determine whether whole plant yield compensatory responses occur to offset stem-mining reductions. Flag leaf photosynthetic reduction was not detected 16-20 d after infestation, but were detected at 40-42 d and doubled from water or phosphorus stresses. Main stem grain weight decreased from 10 to 25% from stem mining, largely due to reductions in grain size, with greater reductions under low phosphorus and/or water levels. Phosphorus-deficient plants without water stress were most susceptible to C. cinctus, more than doubling the grain weight reduction due to larval feeding relative to other water and phosphorus treatments. Two solid stemmed varieties with stem mining had less grain weight loss than a hollow stemmed variety, so greater internal mechanical resistance may reduce larval stem mining and plant yield reductions. Our results emphasize the importance of sufficient water and macronutrients for plants grown in regions impacted by C. cinctus. Also, solid stemmed varieties not only reduce wheat lodging from C. cinctus, they may reduce harvested grain losses from infested stems.

Oviposition behavior of the wheat stem sawfly when encountering plants infested with cryptic conspecifics

Insect herbivores typically oviposit on the most suitable hosts, but choices can be modulated by detection of potential competition among conspecifics, especially when eggs are deposited cryptically. Larvae of the wheat stem sawfly, Cephus cinctus Norton, developing within an already infested stem, experience elevated risk when only one will survive because of cannibalism. To increase our understanding of host selection when the choices made by females can lead to severe intraspecific competition, females were presented with either uninfested wheat plants or with plants previously exposed to other females in laboratory choice tests. The oviposition behavior of this insect was described by recording the behavioral sequences that lead to and follow the insertion of the ovipositor in both previously infested and uninfested stems. No significant differences were found in frequencies of specific behaviors or behavioral transitions associated with oviposition. In choice tests, there was no difference in the numbers of eggs laid in infested and uninfested plants. Taller plants received more eggs, irrespective of infestation. Females neither preferred nor avoided previously infested hosts. Other characteristics of the host, such as stem height, may be more important in determining suitability for oviposition. These findings support the use of management tactics relying on the manipulation of oviposition behavior, such as trap cropping. Given that there is no evidence for response to previously infested hosts, the infested plants in a trap crop would remain as suitable as they were when uninfested, which could also lead to an increase in mortality caused by intraspecific competition.

Cultivar preferences of ovipositing wheat stem sawflies as influenced by the amount of volatile attractant

The wheat stem sawfly, Cephus cinctus Norton, causes severe losses in wheat grown in the northern Great Plains. Much of the affected area is planted in monoculture with wheat, Triticum aestivum L., grown in large fields alternating yearly between crop and no-till fallow. The crop and fallow fields are adjacent. This cropping landscape creates pronounced edge effects of sawfly infestations and may be amenable to trap cropping using existing agricultural practices. The behavioral preference for two wheat varieties was assessed in the context of developing trap crops for this insect. In field nurseries, stem lodging assessments indicated that the cultivar 'Conan' was infrequently damaged, whereas 'Reeder' was often heavily damaged. In laboratory choice and no-choice tests, 'Reeder' was significantly preferred by ovipositing wheat stem sawfly females. These two cultivars did not differ significantly in height or developmental stage, factors known to impact sawfly preference. Although Conan received fewer eggs than Reeder in no-choice tests, oviposition was further reduced in choice tests, indicating that females clearly preferred Reeder. In field trials where the overall dimensions of the spatial structure in choice tests was varied, females always selected Reeder over Conan in alternating block, row, and interseeded planting scenarios. Reeder releases greater amounts of the attractive compound, (Z)-3-hexenyl acetate than Conan but is similar to Conan for three other known, behaviorally active volatile compounds. The results are discussed in terms of cultivar selection for large scale trap crop experiments for the wheat stem sawfly.

Mycoses of wheat stem sawfly (Hymenoptera: Cephidae) larvae by Fusarium spp. isolates

A complex of Fusarium spp., including F. pseudograminearum, F. culmorum, F. avenaceum, F. equiseti, and F. acuminatum, was isolated from field-collected larval cadavers of wheat stem sawfly at two locations for 2 yr. The Fusarium spp. isolates caused mortality in both diapausing larvae in a topical bioassay and in developing larvae feeding in infected stems in a greenhouse experiment. Larval mortality was >90% in both experiments at the highest dose. The pattern of correlation between integument discoloration, hyphal growth, and larval mortality showed that the Fusarium spp. isolates actively infect larvae and kill them, rather than colonizing larval tissue as secondary postmortem invaders. The versatility of Fusarium spp. as plant and insect pathogens enables colonization that results in disease in wheat plants and subsequent mortality of the wheat stem sawfly larvae developing within the same tissue.

Impact of Diuraphis noxia and Rhopalosiphum padi (Hemiptera: Aphididae) on primary physiology of four near-isogenic wheat lines

The impact of feeding injury by the Russian wheat aphid, Diuraphis noxia (Mordvilko) (Hemiptera: Aphididae), and bird cherry-oat aphid, Rhopalosiphum padi (L.) (Hemiptera: Aphididae) on susceptible and resistant wheat, Triticum aestivum L., near-isogenic lines 'Tugela' (susceptible), Tugela-Dn1 (antibiotic), Tugela-Dn2 (tolerant), and Tugela-Dn5 (antixenotic) was evaluated by assessing photosynthetic parameters. Photosynthesis and closely related parameters, pigment composition, and nonstructural carbohydrates were measured at 1, 3, and 9 d after aphids were introduced on plants maintained under greenhouse conditions. Overall, R. padi had a higher reproductive capacity within a period of 9 d compared with D. noxia on all lines except Tugela-Dn2. Although the visible injury symptoms associated with aphid injury can be highly species specific, the data indicate that photosynthetic reduction is a common physiological pattern of wheat response to aphid feeding, irrespective of chlorosis elicitation. Although both aphids negatively affected net photosynthesis, D. noxia had a greater impact than R. padi, even when aphid numbers were considerably fewer for D. noxia (100-150 aphids per plant) compared with R. padi (> 200 aphids per plant). The photosynthetic pigment and carbohydrate data suggest that the initial net photosynthesis reduction elicited by aphid feeding may not be directly related to the light reaction portion of the photosynthetic pathway via pigment losses. It is also unlikely that source-sink manipulation is the primary cause for the observed short-term inhibition of photosynthesis.

Photosynthetic responses of wheat, Triticum aestivum L., to defoliation patterns on individual leaves

The impact of defoliation by fall armyworm, Spodoptera frugiperda (J. E. Smith), on the photosynthetic rates of injured, individual wheat, Triticum aestivum L., leaves and the impact of different spatial patterns of artificial insect defoliation on photosynthesis of remaining leaf tissue of injured, individual wheat leaves were evaluated in this study. Photosynthesis, stomatal conductance, transpiration, and chlorophyll a fluorescence were recorded in the flag-leaves of wheat plants 1 and 24 h after defoliation in 2003 and at 1 h, 24 h, 7 d, and 14 d after defoliation in 2004. Photosynthesis of injured leaves was not significantly affected by any defoliation treatment (i.e., control, natural, and artificial). Similarly, we did not observe interactions between defoliation treatments and time after defoliation. Stomatal conductance was significantly affected by time after defoliation and by the interaction between defoliation treatment and time after defoliation. However, in general, our results showed that wheat responded similarly to insect defoliation and artificial defoliation, which, therefore, may be used to simulate leaf mass consumption. Spatial defoliation patterns had a significant effect on photosynthetic parameters of injured leaves, but responses were dependent on plant developmental stages. The chlorophyll a fluorescence data revealed no significant effects from any defoliation pattern on the photochemical efficiency of the injured leaf. No significant interactions between defoliation patterns and time after defoliation were observed. Our findings reveal that the spatial pattern of defoliation in wheat affects photosynthetic and other gas exchange responses, which suggests that when simulating insect defoliation in wheat, researchers need to be cognizant of the defoliation pattern to adequately simulate insect defoliation.

Performance of an analytical, dual infrared-beam, stored-product insect monitoring system

A system is described for automated monitoring of pest insects in stored grain. It provides quantitative data indicative of the species of detected insects and is self-calibrating to maintain reliable operation over time across adverse environmental and biological conditions. The system uses electronic grain probes, each with a dual infrared-beam sensor head providing orthogonal views of falling insects. Sensor analog signals are analyzed by an embedded microprocessor, and extracted waveform parameters are transmitted back to a central computer. Filtering algorithms recognize and eliminate false detections due to extraneous (nonfalling) insect activities and provide an indication of species based on body size. Laboratory test data provide species identification templates and an analysis of Montana field test data acquired in aerated and nonaerated bins demonstrates the effectiveness of the filtering algorithms. The described system technology has been licensed by OPIsystems, Inc., Calgary, Alberta, Canada, and is commercially available as Insector.

Assessment of health and growth of ring-necked pheasants following consumption of infected insects or conidia of entomopathogenic fungi, Metarhizium anisopliae var. acridum and Beauveria bassiana, from Madagascar and North America

Isolates of two fungi (Beauveria bassiana and Metarhizium anisopliae var. acridum) from Madagascar are being developed for control of grasshoppers and locusts, as part of a search for alternatives to environmentally detrimental chemical insecticides. The probable effects of these entomopathogens on nontarget species must be determined before operational use. Birds may become exposed to these fungi either directly, by consuming spores deposited on their food items, or secondarily, by consuming grasshoppers or locusts that have died from infection by these biocontrol agents. This article presents the results of per os challenge from fungus-infected food items. Male and female ring-necked pheasants (Phasianus colchicus) were exposed at 4 d of age and again at 9 d of age to challenge treatments, or 2 control treatments (18 male and 18 female birds per treatment group). Pheasants were weighed at 9, 17, and 25 d of age, tarsal length was measured at 25 d of age, and they were observed daily for signs of adverse effects of the experimental treatments. At the time of euthanasia (25 d of age), 2 or 3 randomly selected birds from each of the groups exposed to infected grasshoppers, plus the 2 control groups, underwent complete necropsies and histopathological examination of 16 tissues from each bird. Results show that in both sexes, weight gain at both 17 and 25 d was not significantly different between challenge groups and control groups. Tarsal length at 25 d of age, an indication of structural growth, was also not markedly different among challenged and control groups. Histopathological changes were generally undetectable, mild, or moderate, and not consistently associated with any treatment. Based on these findings, there is little indication that birds are susceptible to detrimental health effects from direct or secondary exposure to the two entomopathogenic fungi studied.

Parasitism of the wheat stem sawfly (Hymenoptera: Cephidae) by Bracon cephi and B. lissogaster (Hymenoptera: Braconidae) in wheat fields bordering tilled and untilled fallow in Montana

We evaluated wheat stem sawfly, Cephus cinctus Norton, parasitism, infestation, and sawfly-cut stems in wheat fields bordering intensely tilled (no visible stubble residue), minimally tilled (>75% stubble residue visible), and untilled (chemical fallow, herbicide fallow management) summer fallow fields in north-central and south-central Montana. No difference in sawfly parasitism or sawfly-cut stems was found between fields bordering minimally tilled and fields bordering untilled summer fallow. Sawfly parasitism in fields bordering untilled summer fallow was greater than in fields bordering intensely tilled summer fallow at six of the eight sites examined. Sawfly-cut stems were greater in the field bordering intensely tilled fallow at four sites, with no difference in sawfly-cut stems between the intensely tilled and untilled field at the other four sites. Although it has never been reported, we have observed that many sawfly stubs are completely buried. Therefore, we measured the depth of sawfly stubs in four untilled fields in Broadwater County, MT. Two-thirds of the stubs were completely buried (206 of 300) with an average depth of 6 mm. Intensive tillage, which results in soil-covered stubble, is not an effective sawfly control practice, because sawflies typically overwinter below ground and upon emergence must dig to reach the soil surface. However, Bracon cephi (Gahan) and Bracon lissogaster Muesebeck overwinter above ground in stems and might be unable to dig to the soil surface if buried. The elimination of intensive tillage in favor of chemical fallow should result in greater sawfly parasitism over time. Producers replacing minimal tillage with chemical fallow should see no effect on sawfly parasitism.

Naphthalene, an insect repellent, is produced by Muscodor vitigenus, a novel endophytic fungus

Muscodor vitigenus is a recently described endophytic fungus of Paullinia paullinioides, a liana growing in the understorey of the rainforests of the Peruvian Amazon. This fungus produces naphthalene under certain cultural conditions. Naphthalene produced by M. vitigenus was identified by gas chromatography/mass spectrometry. Its chromatographic and mass spectral properties were identical to authentic naphthalene. Agar plugs supporting growth of the fungus and producing known amounts of naphthalene effectively repelled the adult stage of the wheat stem sawfly, Cephus cinctus, in Y-tube bioassay tests. Authentic naphthalene, at comparable concentrations to those in tests involving the fungus itself, mimicked the insect repellency of the fungus. Although other Muscodor spp. produce volatile antimicrobials, M. vitigenus is unique in its ability to produce naphthalene almost exclusively. This report also describes the potential practical implications of M. vitigenus.

Pheromone components of the wheat stem sawfly: identification, electrophysiology, and field bioassay

Volatiles collections and cuticular extracts of the wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), were analyzed by coupled gas chromatographic-electroantennographic detection (GC-EAD) in order to detect possible pheromone components of this species. Volatiles collections from male and female sawflies contained the same 13 GC-EAD-active compounds that stimulated both male and female antennae. GC-EAD-active compounds were identified by mass spectrometry, and the identities were verified by acquiring or synthesizing authentic standards with identical GC retention times and mass spectra. 9-Acetyloxynonanal gave the strongest EAD response. Additional GC-EAD-active compounds included 13-acetyloxytridecanal, aldehydes with 9-16 carbon chain lengths, acids with 8-10 carbon chain lengths, and phenylacetic acid. The last was instantly detectable by human nose when several males were allowed to interact, but not from isolated insects. On a per-insect basis, grouped males overall released higher amounts of the GC-EAD-active compounds than grouped females. Notable quantitative differences between the sexes were relatively higher amounts of 9-acetyloxynonanal, phenylacetic acid, and tetradecanal from males and hexadecanal from females. In the absence of an absolute, qualitative difference between sexes, these relative differences might be important for sex recognition. Field bioassay demonstrated the attractiveness of 9-acetyloxynonanal for male and female C. cinctus. The major compounds of male and female cuticular extracts showed no GC-EAD activity, but ozonolysis of extracts gave dramatically increased amounts of GC-EAD-active material. Hence, double-bond-containing cuticular compounds are suggested as precursors of the aldehydic pheromone components.

Cuticular hydrocarbons and novel alkenediol iacetates from wheat stem sawfly (Cephus cinctus): natural oxidation to pheromone components

The cuticular lipids of the wheat stem sawfly Cephus cinctus (Hymenoptera: Cephidae) were investigated as part of a chemical ecology project with this species. The major cuticular lipids were n-alkenes and n-alkanes. Alkenes were the most abundant and exhibited dramatic sexual dimorphism. (Z)-9-Tricosene accounted for about half of the total hydrocarbon in males but was nearly absent from females. The dominant alkenes in females were (Z)-9-pentacosene and (Z)-9-heptacosene. The alkane profiles were similar in both sexes, with n-tricosane being the most abundant, followed by n-pentacosane and n-heptacosane. In both sexes, there were minor amounts of alkanes and alkenes with other chain lengths and n-alkadienes of 29 and 31 carbons. In males, about one tenth of the surface lipids consisted of (Z)-9-alkene-1, omega-diol diacetates with 22-, 24-, and 26-carbon chains. The same compounds were also detected from females but in much smaller amounts. The structures of these novel diacetates were proven by synthesis. By analogy to methyl oleate, a well-studied food lipid, the alkenes and diacetates were expected to undergo slow oxidation in air to release specific aldehydes and other volatile products, and these were generally detected in volatiles collected from living sawflies. Atmospheric oxidation of the diacetates was also demonstrated in the absence of sawflies. One product from the diacetates, 9-acetyloxynonanal, was shown in other research to be particularly active electrophysiologically and was also attractive in the field. Aldehydes from the alkenes also showed strong electrophysiological activity. The concept of volatile pheromones originating from heavy, unsaturated cuticular lipids is discussed.

Eavesdropping on insects hidden in soil and interior structures of plants

Accelerometer, electret microphone, and piezoelectric disk acoustic systems were evaluated for their potential to detect hidden insect infestations in soil and interior structures of plants. Coleopteran grubs (the scarabaeids Phyllophaga spp. and Cyclocephala spp.) and the curculionids Diaprepes abbreviatus (L.) and Otiorhynchus sulcatus (F.) weighing 50-300 mg were detected easily in the laboratory and in the field except under extremely windy or noisy conditions. Cephus cinctus Norton (Hymenoptera: Cephidae) larvae weighing 1-12 mg could be detected in small pots of wheat in the laboratory by taking moderate precautions to eliminate background noise. Insect sounds could be distinguished from background noises by differences in frequency and temporal patterns, but insects of similarly sized species could not be distinguished easily from each other. Insect activity was highly variable among individuals and species, although D. abbreviatus grubs tended to be more active than those of O. sulcatus. Tests were done to compare acoustically predicted infestations with the contents of soil samples taken at recording sites. Under laboratory or ideal field conditions, active insects within approximately 30 cm were identified with nearly 100% reliability. In field tests under adverse conditions, the reliability decreased to approximately 75%. These results indicate that acoustic systems with vibration sensors have considerable potential as activity monitors in the laboratory and as field tools for rapid, nondestructive scouting and mapping of soil insect populations.

Insect infestation of stored oats in Florida and field evaluation of a device for counting insects electronically

Automated methods of monitoring stored grain for insect pests will contribute to early detection and aid in management of pest problems. An insect population infesting stored oats at a seed processing plant in north-central Florida was studied to test a device for counting insects electronically (Electronic Grain Probe Insect Counter, EGPIC), and to characterize the storage environment. The device counts insects as they fall through an infrared beam incorporated into a modified grain probe (pitfall) trap and transmits the counts to a computer for accumulation and storage. Eight traps were inserted into the surface of the grain bulk, and the insects trapped were identified and counted manually at weekly intervals. Grain temperature and moisture content also were recorded for each trap location. Manual and automatic counts were compared to estimate error in the EGPIC system. Both over- and undercounting occurred, and errors ranged from -79.4 to 82.4%. The mean absolute value of error (+/- SE) was 31.7% (+/- 4.3). At least 31 species, or higher taxa, were detected, but the psocid Liposcelis entomophila (Enderlein) and the foreign grain beetle, Ahasverus advena (Waltl), accounted for 88% of the captured insects. Species diversity, phenology, and spatial distribution are presented, as well as temporal and spatial distribution of grain temperature and moisture content. The data sets generated will find application in population modeling and development of integrated pest management systems for stored grain.

Phenology and spatial pattern of Typhaea stercorea (Coleoptera: Mycetophagidae) infesting stored grain: estimation by pitfall trapping

The hairy fungus beetle, Typhaea stercorea (L.), occurs frequently in stored grain, often in large numbers. Populations infesting stored barley in Minnesota, corn in South Carolina, and wheat in Florida were sampled by means of grain probe traps. Spatial distribution of the species was examined by contour analysis of trap catch. In South Carolina, corn was sampled at 2 locations over 2 storage seasons, and temperature, moisture content, and malathion residues were measured. These data were used to examine phenology as well as spatial distribution, and showed peak trap catch shortly after harvest in the fall, and in the spring. This pattern followed seasonal changes in grain temperature, but there was no apparent relationship of trap catch to either grain moisture content or malathion residue. The populations of T. stercorea were not distributed randomly, but were largely concentrated in 1 or very few aggregations associated with the "spoutline," a region high in foreign material and broken grain that forms near the center of a bin as it is loaded. However, the spatial patterns were dynamic, even on a very small time scale (week to week). Numbers of insects in aggregations rose and fell, the areas involved expanded and contracted, the centers shifted, and secondary centers appeared and disappeared. These changes were apparently in response to changing patterns of grain temperature and moisture content. Secondary centers of aggregation often formed in warmer grain along bin walls.

Thermal treatments to increase acoustic detectability of Sitophilus oryzae (Coleoptera: Curculionidae) in stored grain

Hidden infestations of stored-product insect larvae are detected most rapidly by acoustic techniques when the larvae are highly active. Larval activity is periodic, however, and it tends to decrease after the larvae are disturbed or cooled. Because of the practical need for rapid inspection of grain at commercial elevators, several heat treatments were tested as potential methods of increasing larval activity and improving the speed and reliability of acoustic detection under adverse conditions. Samples of grain infested with 4th instars of Sitophilus oryzae (L.) were exposed to different radiant and convective heat treatments after they had been conditioned at 11 degrees C, 17 degrees C, or room temperature for 12-24 h. Relative activity levels were evaluated over periods of 0-12 h based on the mean levels in a 15-min interval, 2 h after the beginning of a trial. In comparisons among treatments with precooled larvae, relative activity levels 5-10 min after brief heat pulses were 2-30 times higher than activity levels in precooled controls exposed only to ambient temperatures (25 degrees C). After 15-25 min, the relative activity levels of these heated larvae remained 2-5 times higher than those of the ambient controls. Brief movement disturbances inhibited activity for approximately 20 min at any temperature. These results suggest that, in general, larval detectability is enhanced if cool grain samples are warmed and all samples are left undisturbed for 15-20 min before inspection.