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

Evaluation of The Diversity of Durum Wheat Coleoptera (Triticum Durum Desf.) in the Region of Sigus Oum El Bouaghi (Eastern Algeria)

The Oum El Bouaghi region in Eastern Algeria, long considered as a cereal-growing area is nowadays a durum wheat production region par excellence. Although the damage caused by Coleoptera is very significant, studies on the knowledge of their diversity are few and remain limited for some entomological groups. Our work is the first step to evaluate the diversity of Coleoptera and the long-term impact of taking biological management measures against harmful fauna in favour of more environment friendly agriculture. To assess the beetle community, different sampling methods were combined (Barber trap, coloured traps, mowing net and sight hunting). Evaluation of the results of a single campaign showed that Coleoptera infested with durum wheat vary in abundance and diversity. We identified more than 100 species of Coleoptera belonging to 22 different families for a total number of 5698 individuals belonging mainly to the Carabidae, Curculionidae, Chrysomelidae, Scarabidae and Staphylinidae families. Although the majority of Coleoptera collected are pests of durum wheat crops (47.57%) the case of Tropinota hirta, Notaris sp or Oulema melanopus in particular, there was an interesting presence of predators (28.15%) the case of Carabidae or Staphylinidae in particular even with low relative abundance. The temporal evolution of the Coleoptera showed that the species diversity indicated a peak of abundance at the full tillering stage following an accentuated vegetative development of the host plant, and the presence of weeds. The data collected in this way constitute a basis for a preliminary knowledge of the durum wheat Coleoptera and can thus be used to design pest control strategies.

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.

Effects of mechanical injury and insect feeding on volatiles emitted by wheat plants

We report on changes in the volatiles emitted by wheat plants of the cultivar ‘Tonacja’ after the plants were scraped, pierced or damaged by adults of Oulema melanopus (Linnaeus). The blend of volatiles was dominated by typical green leaf volatiles and in addition contained linalool and B-caryophyllene, but the latter two were released in large amounts only after more than one day of insect feeding. Overall, the plants that had been damaged by the insect released more odors than the plants that were subjected to mechanical damage. Moreover, control plants released significantly lower amounts of volatiles. Scraping of leaves induced higher volatile emission than puncturing the leaves. A Y-tube bioassay was used to evaluate upwind orientation ofadult cereal leafbeetles. Greater number of female 0. melanopus was attracted to (Z)-3-hexenal and (Z)-3 -hexenyl acetate at low concentrations. Higher concentration of these compounds and linalool significantly repelled both females and males.