Electrical signals are vital components of long-distance signaling in plants, enabling rapid systemic responses to environmental stimuli. These signals, which include action potentials (APs), variation potentials (VPs), and system potentials (SPs), that can also combine into electropotential waves (EPWs), are primarily propagated through the vascular system, with the phloem playing a central role. EPWs, encompassing APs, VPs, and SPs, are integral to systemic signaling and inter-organ communication via the phloem, and are closely associated with plant responses to pests and pathogens. The complex architecture of the phloem, embedded deep within plant tissues and surrounded by multiple cell layers, poses significant challenges for direct electrophysiological measurements. Traditional electrophysiological methods for studying electrical long-distance signals often require wounding, which can alter the physiological conditions being measured. The use of aphids as bio-electrodes offers a promising alternative, as it avoids mechanical wounding and allows for flexible selection of measurement points. This chapter highlights the advantages and limitations of various techniques available for studying electrical signals in intact plants, which is essential for understanding how plants respond to environmental stimuli.

Arthropods threaten crop production by feeding on plants and, most importantly, by transmitting viruses. BYDV-PAV is the most prevalent virus species that causes barley yellow dwarf disease, one of the most economically important viral diseases affecting cereals worldwide. Maize plays a central role in BYDV-PAV epidemiology, serving as a “green bridge” for BYDV-PAV and its vector Rhopalosiphum padi in summer. Some studies have reported that the incidence of persistently transmitted viruses may be reduced in plants that are resistant to their insect vectors. In contrast, the choice test applied in our study revealed that R. padi is not repelled by the included BYDV-PAV-resistant maize inbreds. Significant differences in phloem architecture observed among the inbreds suggested that aphids feeding on BYDV-PAV-resistant maize may have difficulties reaching the phloem or establishing a stable feeding site. However, monitoring of aphid feeding behavior using the electrical penetration graph technique on maize inbreds that differed in their BYDV-PAV susceptibility revealed no correlation between R. padi feeding and BYDV-PAV resistance. Furthermore, we could not confirm the generation of reactive oxygen species (ROS), a typical reaction of plants during aphid infestation and infection of some viruses. In summary, we conclude that the BYDV-PAV resistance mechanisms in maize act directly on the virus and not on its vector, R. padi.

Wheat dwarf virus (WDV) causes high yield losses in wheat and other cereals and is therefore an important pathogen transmitted by the leafhopper Psammotettix alienus. Climate change will increase infections by insect-transmitted viruses due to the increasing spread of vectors. In the context of integrated pest management, the cultivation of WDV-resistant/tolerant varieties is an effective way of controlling WDV. Evaluation of tolerant/resistant genotypes is based on inoculation with viruliferous leafhoppers and subsequent phenotyping in gauze houses under semi-field conditions. For successful screening, it is important to ensure the uniform and reproducible inoculation of plants. Abiotic conditions, particularly temperature, have a critical influence on inoculation success, and thus, variations in infection rates were observed within and between previous replicates in the field. Furthermore, the leafhopper population reared in the greenhouse has to be reestablished after each infection, which delays the screening process. We addressed these issues by developing an improved inoculation assay in which plants are inoculated in small infection hoods in the greenhouse before being planted out in gauze houses. This procedure allows optimal environmental conditions for WDV infection of test plants and allows the plants with WDV infection to develop under natural environmental conditions for symptom scoring. In addition, the viruliferous leafhoppers were recollected from the test plants after infection, allowing a sustainable use of the insects. The method thus enables more reliable phenotyping by increasing infection success and testing a greater number of genotypes in a shorter time.

The transmission efficiency of aphid-vectored plant viruses can differ between aphid populations. Intra-species diversity (genetic variation, endosymbionts) is a key determinant of aphid phenotype; however, the extent to which intra-species diversity contributes towards variation in virus transmission efficiency is unclear. Here, we use multiple populations of two key aphid species that vector barley yellow dwarf virus (BYDV) strain PAV (BYDV-PAV), the grain aphid (Sitobion avenae) and the bird cherry-oat aphid (Rhopalosiphum padi), and examine how diversity in vector populations influences virus transmission efficiency. We use Illumina sequencing to characterize genetic and endosymbiont variation in multiple Si. avenae and Rh. padi populations and conduct BYDV-PAV transmission experiments to identify links between intra-species diversity in the vector and virus transmission efficiency. We observe limited variation in the transmission efficiency of Si. avenae, with transmission efficiency consistently low for this species. However, for Rh. padi, we observe a range of transmission efficiencies and show that BYDV transmission efficiency is influenced by genetic diversity within the vector, identifying 542 single nucleotide polymorphisms that potentially contribute towards variable transmission efficiency in Rh. padi. Our results represent an important advancement in our understanding of the relationship between genetic diversity, vector-virus interactions, and virus transmission efficiency.

Barley yellow dwarf (BYD) is one of the economically most important virus diseases of cereals worldwide, causing yield losses of up to 80 %. BYD is caused by at least ten different phloem-limited viruses called BYD viruses (BYDVs) and Cereal yellow dwarf viruses (CYDVs). Means to control BYD are limited and the use of genetically resistant cultivars is the most economic and environmentally friendly approach. Maize plays a central role in the BYD infection cycle, serving as a reservoir for BYD-causing viruses and their vectors in summer. Growing BYD resistant maize varieties would reduce BYD pressure on maize and cereals. Using two biparental mapping populations, we were able to reduce a previously published QTL for BYDV-PAV resistance in maize to ~0.3 Mbp, comprising nine genes. Association mapping and gene expression analysis further reduced the number of candidate genes for BYDV-PAV resistance in maize to two: Zm00001eb428010 and Zm00001eb428020. Predicted functions of these genes suggest that they confer BYDV-PAV resistance either via interfering with virus replication or induction of ROS signaling. The sequence of one of these genes, Zm00001eb428010, is affected by a 54 bp deletion in the 5`-UTR and a protein altering variant in BYDV-PAV resistant maize inbreds but not BYDV-PAV susceptible and BYDV-PAV tolerant inbreds. This suggests that altered abundance and/or properties of the proteins that are encoded by Zm00001eb428010 may lead to BYDV-PAV resistance.

BACKGROUND Sugar beet (Beta vulgaris ssp. vulgaris), a key crop for sugar production, faces significant yield losses caused by the black bean aphid Aphis fabae (Scop.) and the green peach aphid Myzus persicae (Sulzer) which also transmit viruses. The restriction on neonicotinoid use in Europe has intensified this problem, emphasizing the urgent need for breeding resistant crop varieties. This study evaluated 26 sugar beet germplasm for resistance against both aphid species by using performance and feeding behavior assays. Additionally, whole plant bioassays and semi-field experiments were carried out with M. persicae. RESULTS Our findings demonstrate the presence of temporal resistance against both aphid species in the primary sugar beet gene pool. Beet yellows virus (BYV) carrying aphids showed enhanced performance. Different levels of plant defense mechanisms were involved including resistance against M. persicae before reaching the phloem, particularly in sugar beet line G3. In contrast, resistance against A. fabae turned out to be predominately phloem-located. Furthermore, a high incidence of black inclusion bodies inside the stomach of M. persicae was observed for approx. 85% of the plant genotypes tested, indicate a general and strong incompatibility between sugar beet and M. persicae in an initial phase of interaction. CONCLUSION Sugar beet resistance against aphids involved different mechanisms and is species-specific. The identification of these mechanisms and interactions represents a crucial milestone in advancing the breeding of sugar beet varieties with improved resistance. This article is protected by copyright. All rights reserved.

KEY MESSAGE:We mapped Ryd4Hb in a 66.5 kbp interval in barley and dissociated it from a sublethality factor. These results will enable a targeted selection of the resistance in barley breeding. Virus diseases are causing high yield losses in crops worldwide. The Barley yellow dwarf virus (BYDV) complex is responsible for one of the most widespread and economically important viral diseases of cereals. While no gene conferring complete resistance (immunity) has been uncovered in the primary gene pool of barley, sources of resistance were searched and identified in the wild relative Hordeum bulbosum, representing the secondary gene pool of barley. One such locus, Ryd4Hb, has been previously introgressed into barley, and was allocated to chromosome 3H, but is tightly linked to a sublethality factor that prevents the incorporation and utilization of Ryd4Hb in barley varieties. To solve this problem, we fine-mapped Ryd4Hb and separated it from this negative factor. We narrowed the Ryd4Hb locus to a corresponding 66.5 kbp physical interval in the barley 'Morex' reference genome. The region comprises a gene from the nucleotide-binding and leucine-rich repeat immune receptor family, typical of dominant virus resistance genes. The closest homolog to this Ryd4Hb candidate gene is the wheat Sr35 stem rust resistance gene. In addition to the fine mapping, we reduced the interval bearing the sublethality factor to 600 kbp in barley. Aphid feeding experiments demonstrated that Ryd4Hb provides a resistance to BYDV rather than to its vector. The presented results, including the high-throughput molecular markers, will permit a more targeted selection of the resistance in breeding, enabling the use of Ryd4Hb in barley varieties.

Insect monitoring has gained global public attention in recent years in the context of insect decline and biodiversity loss. Monitoring methods that can collect samples over a long period of time and independently of human influences are of particular importance. While these passive collection methods, e.g. suction traps, provide standardized and comparable data sets, the time required to analyze the large number of samples and trapped specimens is high. Another challenge is the necessary high level of taxonomic expertise required for accurate specimen processing. These factors create a bottleneck in specimen processing. In this context, machine learning, image recognition and artificial intelligence have emerged as promising tools to address the shortcomings of manual identification and quantification in the analysis of such trap catches. Aphids are important agricultural pests that pose a significant risk to several important crops and cause high economic losses through feeding damage and transmission of plant viruses. It has been shown that long-term monitoring of migrating aphids using suction traps can be used to make, adjust and improve predictions of their abundance so that the risk of plant viruses spreading through aphids can be more accurately predicted. With the increasing demand for alternatives to conventional pesticide use in crop protection, the need for predictive models is growing, e.g. as a basis for resistance development and as a measure for resistance management. In this context, advancing climate change has a strong influence on the total abundance of migrating aphids as well as on the peak occurrences of aphids within a year. Using aphids as a model organism, we demonstrate the possibilities of systematic monitoring of insect pests and the potential of future technical developments in the subsequent automated identification of individuals through to the use of case data for intelligent forecasting models. Using aphids as an example, we show the potential for systematic monitoring of insect pests through technical developments in the automated identification of individuals from static images (i.e. advances in image recognition software). We discuss the potential applications with regard to the automatic processing of insect case data and the development of intelligent prediction models.

Wheat dwarf virus (WDV) causes an important vector transmitted virus disease, which leads to significant yield losses in barley production. Due to the fact that, at the moment, no plant protection products are approved to combat the vector Psammotettix alienus, and this disease cannot be controlled by chemical means, the use of WDV-resistant or -tolerant genotypes is the most efficient method to control and reduce the negative effects of WDV on barley growth and production. In this study, a set of 480 barley genotypes were screened to identify genotypic differences in response to WDV, and five traits were assessed under infected and noninfected conditions. In total, 32 genotypes showed resistance or tolerance to WDV. Subsequently, phenotypic data of 191 out of 480 genotypes combined with 34,408 single-nucleotide polymorphisms (SNPs) were used for a genome-wide association study to identify quantitative trait loci (QTLs) and markers linked to resistance/tolerance to WDV. Genomic regions significantly associated with WDV resistance/tolerance in barley were identified on chromosomes 3H, 4H, 5H, and 7H for traits such as relative virus titer, relative performance of total grain weight, plant height, number of ears per plant, and thousand grain weight.

AbstractVirus diseases are causing high yield losses in crops worldwide. TheBarley yellow dwarf virus(BYDV) complex is responsible for one of the most widespread and economically important viral diseases of cereals. While no complete resistance gene has been uncovered in the primary genepool of barley, sources of resistance were identified in the wild relativeHordeum bulbosum, representing the secondary genepool of barley. One such locus,Ryd4Hb, has been previously introgressed into barley, and was allocated to chromosome 3H, but is tightly linked to a sublethality factor that prevents the incorporation and utilization ofRyd4Hbin barley varieties. To solve this problem, we fine-mappedRyd4Hband separated it from this negative factor. We narrowed theRyd4Hblocus to a 66.5 kbp physical interval in the barley ‘Morex’ reference genome. The region comprises one complete and one partial gene from the nucleotide-binding and leucine-rich repeat immune receptor family, typical of dominant virus resistance genes. The closest homolog to these twoRyd4Hbcandidate genes is the wheatSr35stem rust resistance gene. In addition to the fine mapping, we reduced the sublethality factor interval to 600 kbp in barley. Aphid feeding experiments demonstrated thatRyd4Hbprovides a direct resistance to BYDV rather than a resistance to its vector. The presented results, including the high-throughput molecular markers, will permit a more targeted selection of the resistance in breeding, enabling the use ofRyd4Hbin barley varieties.Key messageWe mappedRyd4Hbin a 66.5 kpb interval in barley and dissociated it from a sublethality factor. These results will enable a targeted selection of the resistance in barley breeding.

Increasing evidence suggests that land-use intensification contributes to destabilization of trophic networks of insect communities in agriculture resulting in a loss of biodiversity. However, a more detailed understanding of the causes and consequences of the widely reported insect decline is still lacking. Here, we used standardised daily long-term data on the activity of flying insects (~ 250 d/year) to describe the interactive effects of climate warming in intensively cultivated regions and changes in predatory taxa on the general long-term trend of insects and the regulation of herbivores. While the intensely managed landscapes examined in this study show a substantial decline in several taxonomic groups (95.1% total biomass loss in 24 year), the data on aphids support a general assumption that biodiversity loss is often closely associated with arising pest problems. Aphids being pests in agroecosystems develop earlier in spring in overall higher annual abundances. The data highlight that regional insect abundances have declined over recent decades in agricultural landscapes, thus indicating fundamental effects on food webs and insect herbivore performance.

The modulation of nutritional intake by animals to combat pathogens is a behaviour that is receiving increasing attention. Ant studies using isolated compounds or nutrients in artificial diets have revealed a lot of the dynamics of the behaviour, but natural sources of medicine are yet to be confirmed. Here we explored whether Formica fusca ants exposed to a fungal pathogen can use an artificial diet containing foods spiked with different concentrations of crushed aphids for a medicinal benefit. We show that pathogen exposed colonies adjusted their diet to include more aphid supplemented foods during the acute phase of the infection, reducing the mortality caused by the disease. However, the benefit was only attained when having access to a varied diet, suggesting that while aphids contain nutrients or compounds beneficial against infection, it is a part of a complex nutritional system where costs and benefits of compounds and nutrients need to be moderated.

Abstract Sugar beet (Beta vulgaris ssp. vulgaris), a key crop for sugar production, faces significant yield losses by the green peach aphid Myzus persicae (Sulzer) and black bean aphid Aphis fabae (Scop.) as well as the transmission of virus by these aphids. The restriction on the use of neonicotinoids in Europe has intensified this problem, emphasizing the urgent requirement for breeding resistant crop varieties. This study evaluated sugar beet germplasm for resistance against these two aphid species. We investigated the performance and feeding behavior of both species on 26 sugar beet genotypes, using leaf disk bioassays and electropenetrography studies. Additionally, whole plant bioassays and semi-field experiments were carried out with M. persicae. Our findings demonstrate the presence of temporal resistance against both aphid species in the primary sugar beet gene pool. We also found that carrying the beet yellows virus (BYV) enhanced the aphids’ performance. Different plant defense mechanisms were involved: resistance against M. persicae primarily occurred prior to the stylet reaching the phloem, particularly in sugar beet line G3. While resistance against A. fabae turned out to be predominately phloem-located. A high incidence of black stomach symptoms in aphids, exceeding 85% across all genotypes, signified a general incompatibility between sugar beet and M. persicae. In conclusion, sugar beet resistance against aphids involved different mechanisms and was aphid-specific. The identification of these mechanisms and interactions represents a crucial milestone in advancing the breeding of sugar beet varieties with improved resistance.

Wheat dwarf disease (WDD) is an important disease of monocotyledonous species, including economically important cereals. The causative pathogen, wheat dwarf virus (WDV), is persistently transmitted mainly by the leafhopper Psammotettix alienus and can lead to high yield losses. Due to climate change, the periods of vector activity increased, and the vectors have spread to new habitats, leading to an increased importance of WDV in large parts of Europe. In the light of integrated pest management, cultivation practices and the use of resistant/tolerant host plants are currently the only effective methods to control WDV. However, knowledge of the pathosystem and epidemiology of WDD is limited, and the few known sources of genetic tolerance indicate that further research is needed. Considering the economic importance of WDD and its likely increasing relevance in the coming decades, this study provides a comprehensive compilation of knowledge on the most important aspects with information on the causal virus, its vector, symptoms, host range, and control strategies. In addition, the current status of genetic and breeding efforts to control and manage this disease in wheat will be discussed, as this is crucial to effectively manage the disease under changing environmental conditions and minimize impending yield losses.

Wheat dwarf virus (WDV) is transmitted by the leafhopper Psammotettix alienus. As a major pathogen in wheat and other cereals, WDV causes high yield losses in many European countries. Due to climate change, insect-transmitted viruses will become more important and the restrictions in the use of insecticides efficient against P. alienus renders growing of WDV resistant/tolerant varieties the only effective strategy to control WDV. So far, there is little information about the possible sources of resistance and no known information about the genome regions responsible for the resistance. In a screening for WDV resistance using artificial inoculation in gauze houses, a panel of 500 wheat accessions including cultivars, gene bank accessions, and wild relatives of wheat was phenotyped for virus titer, infection rate, as well as plant height and yield parameters relative to healthy controls of the same genotype. Additionally, 85 T. aestivum-Ae. tauschii intogression lines were tested for WDV resistance in the greenhouse. A subset of 250 hexaploid wheat accessions was genotyped with the 15k iSelect SNP Chip. By genome-wide association study (GWAS), the quantitative trait loci (QTL) for partial WDV resistance were identified. Within these studies, one cultivar was identified showing an average infection rate of only 5.7%. By analyzing single seed descent (SSD) and doubled haploid (DH) populations comprising 153 and 314 individuals for WDV resistance and by genotyping these with the 25k iSelect SNP Chip, QTL for yield per plant, thousand-grain weight, and relative virus titer were validated on chromosomes 1B, 2B, 3B, 4B, 4A, 5A, 6A, and 7A. These results will be the basis for marker-assisted selection for WDV resistance to replacing the laborious, time-consuming, and technically challenging phenotyping with WDV bearing leafhoppers.

In laboratory conditions, ants can combat a pathogen infection by means of the medicinal use of reactive oxygen species (ROS). However, it is still unknown where they obtain medicinal compounds in the wild and how they use them. Due to an upregulation of ROS in response to herbivory, aphid-infested plants have been suggested to be a potential source of ROS for ants in the wild. We investigated whether infection would cause Lasius platythorax ants to change their foraging on extrafloral nectar on aphid-infested plants. We found no clear evidence for the ants significantly changing their foraging behaviour in response to the pathogen, nor for the extrafloral nectar to contain ROS. The aphids in our experiment had a relatively high concentration of ROS and future research should determine whether predation on aphids could be a potential source of both protein and ROS needed to combat a disease.

In the past, breeding for incorporation of insect pest resistance or tolerance into cultivars for use in integrated pest management schemes in oilseed rape/canola (Brassica napus) production has hardly ever been approached. This has been largely due to the broad availability of insecticides and the complexity of dealing with high-throughput phenotyping of insect performance and plant damage parameters. However, recent changes in the political framework in many countries demand future sustainable crop protection which makes breeding approaches for crop protection as a measure for pest insect control attractive again. At the same time, new camera-based tracking technologies, new knowledge-based genomic technologies and new scientific insights into the ecology of insect-Brassica interactions are becoming available. Here we discuss and prioritise promising breeding strategies and direct and indirect breeding targets, and their time-perspective for future realisation in integrated insect pest protection of oilseed rape. In conclusion, researchers and oilseed rape breeders can nowadays benefit from an array of new technologies which in combination will accelerate the development of improved oilseed rape cultivars with multiple insect pest resistances/tolerances in the near future.