Main conclusion Coleoptera, the largest and the most diverse Insecta order, is characterized by multiple adaptations to plant feeding. Insect-associated microorganisms can be important mediators and modulators of interactions between insects and plants. Interactions between plants and insects are highly complex and involve multiple factors. There are various defense mechanisms initiated by plants upon attack by herbivorous insects, including the development of morphological structures and the synthesis of toxic secondary metabolites and volatiles. In turn, herbivores have adapted to feeding on plants and further sophisticated adaptations to overcome plant responses may continue to evolve. Herbivorous insects may detoxify toxic phytocompounds, sequester poisonous plant factors, and alter their own overall gene expression pattern. Moreover, insects are associated with microbes, which not only considerably affect insects, but can also modify plant defense responses to the benefit of their host. Plants are also frequently associated with endophytes, which may act as bioinsecticides. Therefore, it is very important to consider the factors influencing the interaction between plants and insects. Herbivorous insects cause considerable damage to global crop production. Coleoptera is the largest and the most diverse order in the class Insecta. In this review, various aspects of the interactions among insects, microbes, and plants are described with a focus on coleopteran species, their bacterial symbionts, and their plant hosts to demonstrate that many factors contribute to the success of coleopteran herbivory.

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.

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.

Plants and insects have been coexisting for more than 350 million years. During this time, both have evolved many strategies to successfully exploit or respond to reciprocal adaptation and defense reactions. Plants tend to minimize the damage caused by pest feeding, while pests tend to manipulate plant response by suppressing plant defense mechanisms or developing strategies to overcome plant defense systems. Plants recognize insect pests by the wounding that they cause and elicitors present in pest oral secretions (saliva and/or regurgitant). These elicitors or insect-associated microorganisms can modulate plant response to the benefit of their insect hosts. In this article, we have undertaken an analysis of gene expression in serine and cysteine proteinase inhibitors (SerPI and CysPI, respectively) in wheat (Triticum aestivum) plants exposed to cereal leaf beetle (CLB, Oulema melanopus, Coleoptera, Chrysomelidae) larvae feeding, and the impact of microbes associated with CLB on the expression levels of these genes. Using three wheat varieties and antibiotic-treated and untreated CLB larvae, we found that SerPI plays a more important role than CysPIs in plant defense against CLB larvae. Additionally, higher levels of SerPI gene expression were observed in systemic leaves in comparison to the wounded leaves (local response). Each of the tested wheat varieties reacted in a specific way to the particular treatment. Moreover, the presence of microbial components associated with insects influenced plant response to CLB larvae feeding.

Wheat production is threatened by the destructive effects of numerous pests, including Oulema melanopus (cereal leaf beetle, CLB). Both adults and larvae of CLB damage grain crops, but the target of insecticide treatments are the larvae. Insect-associated bacteria are important for many of the insects’ life processes and may also modulate plant defense responses to feeding of their insect host. The aim of our study was to elucidate the early wheat plants’ reaction to this herbivore feeding and to disclose the CLB-associated bacteria modulation of the wheat-insect interactions. Transcriptome analyses were performed for the leaves wounded mechanically and by feeding of the CLB larvae as well as for the distal leaves to study both, the plant’s local and systemic response. Comparative transcriptome analysis indicated that 24 h after the plant treatment, a much larger number of up-regulated DEGs in damaged leaves was noted, especially those on which larvae were fed. It may suggest that at the analysed time point, the local response was stronger than the systemic one. In the leaves on which larvae with natural bacterial flora were fed (local response), the number of up- and down-regulated differentially expressed genes (DEGs) was 7136 and 7411, respectively, in comparison to the dataset obtained for the leaves wounded by larvae with a reduced number of bacteria. In the distal leaves, 3015 up- and 2372 down-regulated DEGs were noted. CLB-associated bacteria were found to affect many aspects of the physiology of wheat plants, especially in wounded leaves, including the expression of genes related to primary metabolism, phytohormone signaling and photosynthesis. We also observed that CLB-associated bacteria mitigated numerous anti-herbivore processes and pathways associated with the synthesis of metabolites and proteins, potentially harmful to the insects. The bacteria also reversed the expression of some genes involved, inter alia, in the phosphorylation of proteins, oxidative stress, cell wall organization, and biogenesis. Understanding the role of CLB-associated bacteria in the plant’s defense response will be important to the fields of pest control and herbivore and its host ecology and evolution.

The aim of this study was to analyze the effects of different variants of insecticidal treatment against Agrotis spp. caterpillars on the technological yield from sugar beet using the AMMI (Additive Main Effect and Multiplicative Interaction) model. Data for the analysis of sugar beet yield and different insecticidal treatments were obtained from a trial in Winna Góra between 2011 and 2018. White sugar yield was estimated for each variant of treatment, and it was found to be directly proportional to the root weight and polarization. The content of potassium in molasses had an inversely proportional effect on the sugar yield in the variant of treatment based on phenological observations with calculated heat sums, as well as in controls. The content of α-amino-N had an inversely proportional effect on the technological yield of sugar for each variant of tested chemical treatments. The content of α-amino-N had a statistically significant effect on the sugar beet yield for all tested experimental combinations. AMMI analysis used to estimate the interaction of treatments based on environmental conditions showed the additive effect of the applied treatments on the quality parameters of white sugar yield from sugar beet. These effects were demonstrated for polarization and the content of sodium in molassigenic substances. Regarding the AMMI model, the results of the analysis of variance showed a significant interaction between treatment and year for all considered characteristics in the experiment.