The structure of the cereal leaf beetle (Oulema melanopus) microbiome depends on the insect’s developmental stage, host plant, and origin

Cereal leaf beetle (CLB, Oulema melanopus, Coleoptera, Chrysomelidae) is a serious agricultural pest that causes considerable damages to agricultural production. The aim of this study was to characterize the bacterial communities associated with larvae and imagoes of CLB collected from various cereal host species and locations. The bacterial profile was characterized by 16S rRNA gene sequencing at the V3-V4 hypervariable region. Using taxonomy-based analysis, the bacterial community of CLB containing 16 phyla, 26 classes, 49 orders, 78 families, 94 genera, and 63 species of bacteria was identified. The abundance of Wolbachia, Rickettsia, and Lactococcus genus was significantly higher in CLB imagoes than in larvae. Statistical analysis confirmed that the bacterial community of the larvae is more diverse in comparison to imagoes and that insects collected from spring barley and wheat are characterized by a much higher biodiversity level of bacterial genera and species than insects collected from other cereals. Obtained results indicated that the developmental stage, the host plant, and the insect’s sampling location affected the CLB’s microbiome. Additionally, the CLB core microbiome was determined. It consists of 2 genera (Wolbachia and Rickettsia) shared by at least 90% tested CLB insects, regardless of the variables analysed.

Foliar Application of Entomopathogenic Nematodes against Cereal Leaf Beetle Oulema melanopus L. (Coleoptera: Chrysomelidae) on Wheat

Cereal monocultures are very susceptible to many pests, especially to those living on leaves, which largely affects yield by decreasing its quality. The most dangerous of them is the cereal leaf beetle (Oulema melanopus L.). In cases of heavy infestation by its larvae, the surface of plants may be reduced by 50%, and sometimes even by 80%, with a main yield loss of 10–25%. The aim of the presented study was to assess the efficiency of a native isolate of Steinernema feltiae (Filipjev, 1934) and commercial preparation Larvanem (Heterorhabditis bacteriophora (Poinar, 1975)) in controlling the larvae of O. melanopus, and to reduce crops damage in the field. Nematodes were applied in a dosage of 2 million IJs/m2 as a suspension of 11 litres per square metre. A hand sprinkler with field lance and flat-stream nozzles was used for applications at the lowest working pressure of 3000 hPa. The effectiveness of both nematode species was moderate: 47.8% for S. feltiae isolate and 49.5% for H. bacteriophora. The biggest reduction in leaf damage was found in crops treated with the commercial preparation, where the index of leaf infection was 32%, being more than twofold smaller than that for the control.

Assessment of Agrocenosis Adaptability of Winter Wheat in the Conditions of the Foothill Zone of the Central Caucasus

This paper presents the results of multi-year research on the adaptability of winter wheat varieties to the conditions of the foothill zone of the Central Caucasus. Characteristics such as ductility and stability were used to assess varieties for conformity to the cultivation conditions. Plant homeostaticity served as the indicator of ontogenetic adaptability. Phenological observations and reports were carried out according to the state variety testing methodology. The species composition of weed vegetation was established using the Agroecological Atlas of Russia. Conventional insect accounting methods were used to consider phytophages and plants damaged by them. It was established that the dominant pests of winter grains in the early periods of vegetation include phytophage bugs and cereal leaf beetle Oulema melanopus L. The maximum number of phytophage bugs was noted during the earing-flowering period. The proportion of pathogens of spike Fusarium head blight, tan spot and Septoria spot prevailed in the pathogenic complex. In total, 36.7% of varieties, including Kuma, Deya, Esaul, Starshina, Delta, Nota and Antonina, were medium-resistant to Fusarium head blight damage. According to the results of a comprehensive assessment of winter wheat selection by the parameters of adaptability, productivity and resistance to diseases, highly plastic genotypes responsive to environmental factors were distinguished: Kuma, Deya, Veda, Tanya, and List 25 (bi = 2.2; 2,3; 2,1). The selection of varieties was based on the adaptive properties of winter wheat. Fusarium head blight decreased by 20.8% in the mixed variety Batko+Deya, and the yield of mixed variety crops increased by 9%. Methods for compiling mixed varieties and designing the mosaics of varieties in the area of grain agrocenosis are recommended. Keywords: winter wheat, sustainability of agrocenosis, productivity, ecological plasticity, mixed varieties

Pantoea ananatis, A New Bacterial Pathogen Affecting Wheat Plants (Triticum L.) in Poland

Wheat (Triticum aestivum) is one of the most economically important crops in the world. During the routine monitoring of wheat pest, the cereal leaf beetle (CLB, Oulema melanopus, Coleoptera, Chrysomelidae), in the Greater Poland region, it was observed that some leaves wounded by CLB also displayed brownish lesions with clear margins and yellow halo, disease symptoms resembling a bacterial infection. The aim of this study was therefore to investigate those symptoms to establish a causal agent of the disease. The identification based on the results of the Biolog’s Gen III system, 16S rRNA, and gyrB genes sequencing, revealed the presence of eight strains of Pantoea ananatis bacteria. Four strains were derived from wheat leaves (Ta024, Ta027, Ta030, Ta046), and four from the CLB’s oral secretion (OUC1, OUD2, OUF2, and OUG1). They shared the nucleotide identity ranging from 99 to 100% to P. ananatis strains deposited in the GenBank database. Additionally, the multi-locus sequence analysis (MLSA) of concatenated sequences of partial atpD, fusA, gyrB, rplB, and rpoB genes was performed. All P. ananatis strains isolated in Poland, grouped into one cluster supported with high bootstrap value. Pathogenicity tests performed on four varieties of wheat plants have identified P. ananatis strains as a causal agent of wheat disease. To our knowledge, this is the first report of P. ananatis affecting wheat plants.

Genetic Architecture of Cereal Leaf Beetle Resistance in Wheat

Wheat production can be severely damaged by endemic and invasive insect pests. Here, we investigated resistance to cereal leaf beetle in a panel of 876 winter wheat cultivars, and dissected the genetic architecture underlying this insect resistance by association mapping. We observed an effect of heading date on cereal leaf beetle infestation, with earlier heading cultivars being more heavily infested. Flag leaf glaucousness was also found to be correlated with resistance. In line with the strong effect of heading time, we identified Ppd-D1 as a major quantitative trait locus (QTL), explaining 35% of the genotypic variance of cereal leaf beetle resistance. The other identified putative QTL explained much less of the genotypic variance, suggesting a genetic architecture with many small-effect QTL, which was corroborated by a genomic prediction approach. Collectively, our results add to our understanding of the genetic control underlying insect resistances in small-grain cereals.

Linear woody landscape elements may help to mitigate leaf surface loss caused by the cereal leaf beetle

Context Woody semi-natural habitats serve as permanent habitats and hibernation sites for natural enemies and, through spillover processes, they play an important role in the biological control of insect pests. However, this service is also dependent on the amount and configuration of the dominating woody habitat types: linear landscape elements (hedgerows, shelterbelts), and more evenly extended plantations. Relating natural enemy action to the landscape context can help to identify the effect of woody habitats on biological control effectiveness. Objectives In the Central European agricultural landscapes such as in the Hungarian lowlands, where our study took place, woody linear elements are characterised by high, while woody areal elements, mostly plantations, by low biological and structural diversity. In this study, we aimed to determine which composition and configuration of woody linear and areal habitats in the landscape may enhance the effect of natural enemy action on plant damage caused by the cereal leaf beetle (CLB, Oulema melanopus). Methods Herbivory suppression by natural enemies was assessed from the leaf damage difference between caged and open treatments. These exclusion experiments were carried out in 34 wheat fields on plants with controlled CLB infections. The results were related to landscape structure, quantified by different landscape metrics of both woody linear and areal habitats inside buffers between 150 and 500 m radii, surrounding the wheat fields. Results The exclusion of natural enemies increased the leaf surface loss caused by CLBs in all fields. Shelterbelts and hedgerows in 150–200 m vicinity of the wheat fields had a strong suppressing effect on CLB damage, while the presence of plantations at 250 m and further rather impeded natural enemy action. Conclusions Our results indicate that shelterbelts and hedgerows may provide a strong spillover of natural enemies, thus contribute to an enhanced biological control of CLBs.

Experimental Assessment of the Economic Injury Level of the Cereal Leaf Beetle (Coleoptera: Chrysomelidae) in Winter Wheat

The cereal leaf beetle, Oulema melanopus L., is an economically important pest species, reducing crop yields in many cereal growing parts of the world. Available studies on yield depression in winter wheat in relation to the density of O. melanopus revealed inconsistent results, creating uncertainty about economic thresholds for pest control. We present results from a series of controlled field trials over a 4-yr period (2014–2017) in Switzerland to examine the impact of artificial defoliation (0, 20, 40, and 60% of flag leaf area removed in 1-m2 field plots) on yield and yield components in winter wheat. The applied defoliation treatments correspond to field infestations levels of approximately 2–6 larvae per stem. Analysis of the combined data from 11 location-years revealed a significant linear decrease in yield per ear with increasing defoliation intensity. Yield per ear declined at a rate of 1.14% (SE = 0.28) per 10 percentage-point increase in defoliation. Similar results were found in a parallel series of field trials in which a 40% defoliation treatment was applied to eight common wheat cultivars. Interestingly, however, three cultivars showed complete tolerance in yield to defoliation. Data from two trials with natural defoliation by larvae revealed equally low levels of yield loss by feeding of O. melanopus. Based on the experimentally derived yield loss function, we calculated economic injury levels for a range of crop values. These will serve as benchmarks in the development of IPM decision-support tools for managing cereal leaf beetles in winter wheat.