Modeling the combined impacts of host plant resistance and biological control on the population dynamics of a major pest of wheat

Identifying novel sources of resistance to wheat stem sawfly in five wild wheat species

BACKGROUND

The wheat stem sawfly (WSS, Cephus cinctus) is a major pest of wheat (Triticum aestivum) and can cause significant yield losses. WSS damage results from stem boring and/or cutting, leading to the lodging of wheat plants. Although solid-stem wheat genotypes can effectively reduce larval survival, they may have lower yields than hollow-stem genotypes and show inconsistent solidness expression. Because of limited resistance sources to WSS, evaluating diverse wheat germplasm for novel resistance genes is crucial. We evaluated 91 accessions across five wild wheat species (Triticum monococcum, T. urartu, T. turgidum, T. timopheevii, and Aegilops tauschii) and common wheat cultivars (T. aestivum) for antixenosis (host selection) and antibiosis (host suitability) to WSS. Host selection was measured as the number of eggs after adult oviposition, and host suitability was determined by examining the presence or absence of larval infestation within the stem. The plants were grown in the greenhouse and brought to the field for WSS infestation. In addition, a phylogenetic analysis was performed to determine the relationship between the WSS traits and phylogenetic clustering.

RESULTS

Overall, Ae. tauschii, T. turgidum and T. urartu had lower egg counts and larval infestation than T. monococcum, and T. timopheevii. T. monococcum, T. timopheevii, T. turgidum, and T. urartu had lower larval weights compared with T. aestivum.

CONCLUSION

This study shows that wild relatives of wheat could be a valuable source of alleles for enhancing resistance to WSS and identifies specific germplasm resources that may be useful for breeding. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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.

Risk assessment of insect pest expansion in alpine ecosystems under climate change

BACKGROUND

Growth in insect pest populations poses a significant threat to ecosystem functions and services, societal development, and food security in alpine regions under climate change. Risk assessments are important prioritization tools for pest management, which must be used to study insect pest expansion in alpine ecosystems under global warming. We used species distribution modeling to simulate the current and future distribution probabilities of 58 insect pest species in the Qinghai Province, China, based on a comprehensive field investigation. Subsequently, general linear modeling was used to explore the relationship between the distribution probability of these species and the damage caused by them. Finally, we assessed the ecological risk of insect pest expansion across different alpine ecosystems under climate change.

RESULTS

Climate change could increase the distribution probabilities of insect pest species across different alpine ecosystems. However, the presence of insect pest species may not correspond to the damage occurrence in alpine ecosystems based on percent leaf loss, amount of stunting, and seedling death of their host species. Significant positive relationships between distribution probability and damage occurrence were found for several of the examined insect pest species. Insect pest expansion is likely to increase extensively in alpine ecosystems under increasing carbon dioxide (CO₂ ) emission scenarios.

CONCLUSION

The relationships between distribution probability and damage occurrence should be considered in species distribution modeling for risk assessment of insect pest expansion under climate change. Our study could improve the effectiveness of risk assessment of insect pest expansion under changing climate conditions. © 2021 Society of Chemical Industry.

Conventional breeding of insect-resistant crop plants: still the best way to feed the world population

Insect-resistant crops feed much of the world, using reduced carbon inputs and providing much greater economic returns on investment. Newer, more efficient efforts are urgently needed to speed development of insect-resistant plants before a projected 30% global population increase. Plant resistance researchers must employ genotyping by sequencing and high-throughput phenotyping to identify, map and track resistance genes. In contrast to maize, rice, vegetables and wheat, limited progress has occurred to develop meaningful levels of pest resistance in cassava, cowpea and pigeonpea - major sources of nutrition for nearly 1 billion people. A knowledge void exists about the effects of climate change (elevated CO₂) on resistant plants, necessitating efforts to understand this stress. Collaborations with social scientists, extension specialists, economists, spatiotemporal modelers, ecologists, and virologists will be required to develop better ways to integrate insect resistant plants into integrated crop pest management programs.