Virulence of Beauveria bassiana Strains Isolated from Cadavers of Colorado Potato Beetle, Leptinotarsa decemlineata

The Colorado potato beetle, Leptinotarsa decemlineata (Say), is a serious, widely distributed pest of potato and other crops. This pest is able to defoliate the host plant and cause severe yield loss. Moreover, the pest quickly becomes resistant to many chemical pesticides. Therefore, the development of novel biopesticides targeting this pest is urgently needed. The purpose of this study was to obtain new strains of the entomopathogenic fungus Beauveria bassiana and assess their efficacy against L. decemlineata adults under laboratory conditions. Twelve strains were isolated from cadavers of Colorado potato beetles collected in potato fields in the Czech Republic. Test beetles were treated by suspensions of conidia at the concentration of 1 × 107 spores per milliliter and their survival was recorded daily for three weeks. The results of the bioassays revealed that all new native strains were pathogenic to L. decemlineata adults and caused mortality up to 100% at the end of the trial period with an LT50 of about 7 days. These strains were more virulent than a reference strain GHA and some of them can be recommended for the development of a new mycoinsecticide against L. decemlineata. Our findings also highlight the importance of searching for perspective strains of entomopathogenic fungi among naturally infected hosts.

Insekticidni proteini in njihova uporaba za zatiranje koloradskega hrošča (Leptinotarsa decemlineata [Say, 1824])

<p class="042abstractstekst">Plants respond to pest attack, among other mechanisms, by producing specific proteins with insecticidal properties. Proteins with toxic effects on insects have also been discovered in many other organisms, especially fungi and bacteria. Due to their biological function, insecticidal proteins represent an important potential in the development of more environmentally friendly plant protection methods. Increasing knowledge about the mode of action of insecticidal proteins and the identification of genes encoding their synthesis enable the breeding of transgenic plants resistant to insect pests and the development of new bioinsecticidal agents. The Colorado potato beetle (<em>Leptinotarsa decemlineata</em>) is one of the most important pests of potato, so the study of such control methods is crucial for the development of sustainable integrated pest management strategies of potato. This review highlights the properties of some groups of insecticidal proteins and their modes of action, and summarizes examples of studies of their use for the control of Colorado potato beetle.</p>

The role of structural variants in pest adaptation and genome evolution of the Colorado potato beetle, Leptinotarsa decemlineata (Say)

Structural variations (SVs) have been associated with genetic diversity and adaptation in diverse taxa. Despite these observations, it is not yet clear what their relative importance is for microevolution, especially with respect to known drivers of diversity, e.g., nucleotide substitutions, in rapidly adapting species. Here we examine the significance of SVs in pesticide resistance evolution of the agricultural super-pest, the Colorado potato beetle, Leptinotarsa decemlineata. By employing a trio-binning procedure, we develop near chromosomal reference genomes to characterize structural variation within this species. These updated assemblies represent >100-fold improvement of contiguity and include derived pest and ancestral non-pest individuals. We identify >200,000 SVs, which appear to be non-randomly distributed across the genome as they co-occur with transposable elements. SVs intersect exons for genes associated with insecticide resistance, development, and transcription, most notably cytochrome P450 (CYP) genes. To understand the role that SVs might play in adaptation, we incorporate an additional 66 genomes among pest and non-pest populations of North America into the SV graph. Single nucleotide polymorphisms (SNPs) and SVs have a similar proportion in coding and non-coding regions of the genome, but there is a deficit of SNPs in SVs, suggesting SVs may be under selection. Using multiple lines of evidence, we identify 28 positively selected genes that include 337 SVs and 442 outlier SNPs. Among these, there are four associated with insecticide resistance. Two of these genes (CYP4g15 and glycosyltransferase-13) are physically linked by a structural variant and have previously been shown to be co-induced during insecticide exposure.

Sustainable Pest Management Using Biodegradable Apitoxin-Loaded Calcium-Alginate Microspheres

Alternatives and replacements for synthetic chemical-based plant protectants are required. In this study biopolymeric microspheres containing arthropod-derived apitoxin are explored as a possible novel environmentally friendly formulation for plant protection. Here we document the optimization process for microencapsulation of apitoxin into a stable formulation, for ready use in agricultural applications. Efficacy trials were carried out on three different beetle species at various developmental stages (Leptinotarsa decemlineata (Say, 1824.), Tenebrio molitor (Linnaeus, 1758.), Sitophilus granarius (Linnaeus, 1758.)). The encapsulated apitoxin has a steady initial and long residual effect, due to the slow release of apitoxin which is one of its main advantages over other conventional control methods. Microspheres loaded with apitoxin have a detrimental effect on insects, of which it is significantly better gastric compared to contact action (due to pH). The results showed that the highest and fastest mortality was obtained when the highest concentrations (0.6%) were applied, chosen to be economically acceptable. These important findings contribute to knowledge on the application and development of encapsulated apitoxin formulations, and their effectiveness, as an alternative eco-friendly control method in agricultural production.

Efficacy of indigenous isolates of Beauveria bassiana (Balsamo) Vuillemin (Deuteromycota: Hyphomycetes) against the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae)

Background The Colorado potato beetle (CPB) Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae) is one of the most damaging pests of potatoes all over the world as well as in Turkey. Both adults and larvae of this pest feed on the foliage of potatoes, and often cause complete defoliation of potato plants, with considerable yield losses of up to 60%. Chemical control of this pest has induced the selection of resistant CPB populations and negative environmental impact. The aim of the present study was to evaluate the pathogenicity of 14 Turkish isolates of Beauveria bassiana (Balsamo) Vuillemin (Deuteromycota: Hyphomycetes) against different stages of CPB under laboratory conditions. Results All isolates were tested as conidial suspensions of (1 × 107 conidia/ml), using spray method. The results from pathogenicity assays showed that virulence of tested isolates was variable, and mortality increased with the time of exposure. The highest mortality was seen in larvae of CPB; however, young larvae (1st and 2nd instars) were more susceptible to fungal isolates than older ones (3rd and 4th instars). Four isolates (BbDm-1, BbDs-2, BbMg-2, and BbMp-1) were more pathogenic than others against L. decemlineata, causing mortalities between 96.7 and 100% in the 2 youngest larval instars, respectively, between 91.7 and 96.7% in the 2 oldest larval instars, respectively, and between 93.3 and 96.7% in 0–48-h-old adults, respectively, 9 days post treatment. Furthermore, these 4 isolates had the most potent egg-hatching inhibitory effects (66.7–90%). The results of molecular phylogenetic analyses based on the ITS region sequence indicated that all tested B. bassiana isolates showed a high similarity (99%) with other B. bassiana isolates in GenBank. Conclusions Results suggested that the 4 B. bassiana isolates were highly virulence and had the potential for biological control of CPB. Further tests under field conditions are recommended to validate the laboratory results.

Comparison of Microbial Communities in Colorado Potato Beetles (Leptinotarsa decemlineata Say) Collected From Different Sources in China

Microbial communities in insects are related to their geographical sources and contribute to adaptation to the local habitat. The Colorado potato beetle (Leptinotarsa decemlineata) (CPB) is a potato pest that causes serious economic losses in Xinjiang Uygur Autonomous Region (XJ) and Heilongjiang Province (HL), China. The influence of microorganisms in the invasion and dispersal of CPB is unclear. We studied microbial communities of CPB collected from nine geographic sources in China using high throughput sequencing technology. Bacteroidetes, Firmicutes, and Proteobacteria were the most dominant phyla, Clostridia, Bacteroidetes, and γ-Proteobacteria were the most dominant classes, Enterobacterales, Lactobacillales, Clostridiales, and Bacteroidales were the most dominant orders, and Enterobacteriaceae, Streptococcidae, Verrucomicrobiaceae, and Rikenellaceae were the most dominant families. There were significant differences, among sources, in the relative abundance of taxa at the genus level. A total of 383 genera were identified, and the dominant bacteria at the genus level were compared between XJ and HL. Pseudomonas was the unique dominant microorganism in the HL area, and the other four microorganisms (Lelliottia, Enterococcus, Enterobacter, and Lactococcus) were common within the 2 regions. Bacterial community diversity in CPB from Urumqi, Jimunai, and Wenquan was higher than diversity in other regions. T-Distributed Stochastic Neighbor Embedding (tSNE) analysis indicated that order and genus were appropriate taxonomic levels to distinguish geographical sources of CPB. These findings provide insight into the diversity of microorganisms of CPB in the differences among geographically isolated populations.